PHYLOGEOGRAPHY, SPECIES DISTRIBUTION MODELLING, MITOCHONDRIAL GENOME EVOLUTION AND CONSERVATION OF THE

FIJIAN FROGS (CERATOBATRACHIDAE)

by

Tamara Osborne-Naikatini

A thesis submitted in fulfillment of the

requirements for the degree of Doctor of Philosophy

Copyright © 2015 by Tamara Osborne-Naikatini

School of Biological and Chemical Sciences Faculty of Science, Technology and Environment

The University of the South Pacific

August 2015

DECLARATION Statement by the Author

I, Tamara Osborne-Naikatini, declare that this thesis is my own work and that to the

best of my knowledge, it contains no material previously published, or substantially

overlapping with material submitted for the award of any degree at any institution,

except where due acknowledgement is made in the text.

Signature ……………………………………. Date …………………………….

Name ……………………………………………………………………………………...

Student ID No ………………………………………………………………………....

Statement by Supervisor

The research in this thesis was performed under my supervision and to my

knowledge is the sole work of the Ms. Tamara Osborne-Naikatini.

Signature ……………………………………. Date …………………………….

Name ……………………………………………………………………………………...

Designation …………………………………………………………………………....

i

Dedication

“When I was a child, I spake as a child, I understood as a

child, I thought as a child: but when I became a man, I put away

childish things.

For now we see through a glass, darkly; but then face to face:

now I know in part; but then shall I know even as also I am known.

And now abideth faith, hope, love, these three; but the greatest

of these is love.”

Corinthians 13 Verses 11-13 (Saint James Bible)

This thesis is dedicated to my late father, William Osborne…

Daddy this is for you.

ii

Acknowledgements

I owe much to all the kind people who have supported me throughout the

many years it took to birth this manuscript. First and foremost to my supervisors:

Professor Peter Lockhart, Ms. Patricia McLenachan, and Dr. Ralph Riley, without

whom this thesis would not be what it is today. I am truly inspired by these amazing

scientists, whose academic achievements have in no way made them less humble or

understanding. Academics like Dr. Glenn Aguilar and Dr. Linton Winder whose

assistance with data analysis and reviewing of several chapters has made this

dissertation better.

To the many generous and open-hearted people that I met whilst travelling

around the Fijian islands chasing frogs, I will be forever grateful for your friendship

and assistance. To the following villages who allowed me access to the forests and

rivers on their lands and to the village communities that housed and fed me and my

guides/ assistants, my lifelong appreciation: Viwa (Viwa Island); Viro, Tavea,

Rukuruku, and Lovoni (Ovalau Island); Tavoro, Lavena, Somosomo, Qeleni, and

Vuna (Taveuni Island); Lovu, Nuvukailagi, Nukuloa, Nawaikama, Sawaieke, and

Malawai (Gau Island); Waisali, Nadi-i-cake, Driti, Nasealevu, Saqani, and Navonu

(Vanua Levu); Vunisea, Nalidi, Wainamakutu, Navunibau, Nadarivatu, Navai, Naga,

and Matokana (Viti Levu).

Thanks and much love to my friends who kept me laughing and sane (in no

particular order): Anna Sahai, Reena Suliano, Kelera Macedru-Buadromo, Scott

Buadromo, Mere Valu, Elenoa Seniloli, Tuverea Tuamoto, Lote Daulako, Awei

Bainivalu-Delaimatuku, Eleazar O’Connor, Maika Daveta and Nunia Thomas. To

all those around me at work and on the various social media networks who supported

me through the last dark days of writing, I am humbled by your support and I will

never forget it. To my close and extended family, I owe you my unconditional love

and my apologies for being absent when I was needed and for being distant while

lost in my head. Especially, my children Liora and Tiana - thank you for giving your

mother something else to obsess about. And of course, to my better half Mr.

Naikatini, without whom I would have given up a long time ago. I could not even

begin to describe how much I owe you but it’s safe to say that when it’s your turn I

will repay you in full… and then some.

iii

Abstract

The Fijian Cornufer (Subgenus Cornufer) species are the easternmost extent

of a native amphibian species in the South Pacific, and are endemic to the Fijian

archipelago. Both species are currently classified by the International Union for the

Conservation of Nature (IUCN) as threatened. There is distinct genetic divergence

between certain island populations, which would suggest that insular isolation has

led to evolution of multiple, additional species. These characteristics along with

traits that identify other Ceratobatrachid frogs (polymorphic colouration, terrestrial

breeding, unique characteristics of larval development, calling patterns), make for a

particularly interesting branch of the anuran tree of life. In this thesis I review the

conservation status of the Fijian frogs synthesising geo-spatial and genetic analyses.

The geo-spatial analyses indicate a need to re-assess the conservation status of the

Fijian tree frog (Cornufer vitiensis), and for a systematic reappraisal of the Fijian

ground frog (Cornufer vitianus). Novel characterisations of genome structure were

generated. The complete mitochondrial genomes for both Fijian Ceratobatrachids

were sequenced, showing a unique gene order for Neobatrachian frogs. This

provides empirical data which may further current understanding of molecular

evolution in neobatachrian lineages. The mitochondrial and nuclear data enable the

identification of Integrated Operational Taxonomic Units (IOTUs) amongst island

populations of both species. All of the genetic markers indicated that the Taveuni

Island populations are divergent, possibly sub-species. Populations of Cornufer on

Vanua Levu Island are likely source populations for the other islands in the Fiji

group, and could well be the founding population of a putative Cornufer colonizing

ancestor. Conservation efforts directed towards the Taveuni and Vanua Levu Island

populations of Cornufer would inevitably safeguard two levels of genetic

distinctiveness: ancestral genotypes with a possible evolutionary history of

hybridization (and the capacity for generating transgressive phenotypes), as well as a

divergent population of C. vitianus.

iv

Abreviations

cytb cytochrome b oxidase

DNA Dioxyribose nucleic acid

IOTU Intergrated operational taxonomic unit

IUCN International Union for the Conservation of Nature

mtDNA Mitochondrial DNA

nDNA Nuclear DNA

RNA Ribose nucleic acid

rRNA Ribosomal RNA

SDM Species distribution model

v

TABLE OF CONTENTS

Dedication i

Acknowledgements ii

Abstract iii

Abbreviations iv

Table of Contents v

List of Figures ix

List of Tables xi

Chapter One - General Introduction 1-21

1.1 The Ceratobatrachids of Fiji 2

1.1.1 Cornufer in the Pacific 2

1.1.2 The Fiji ground frog, Cornufer vitianus 3

1.1.3 The Fiji tree frog, Cornufer vitiensis 11

1.1.4 The taxonomic status of the Fiji frogs 13

1.2 Molecular Systematics of Anurans 13

1.2.1 Evolutionary relationships, molecular taxonomy and

historical biogeography 13

1.2.2 Use of genetics in conservation of endangered anurans 16

1.2.2.1 Mitochondrial and nuclear markers used in

phylogeography 16

1.2.2.2 Phylogeographic analyses: tools to discern

population history and connectivity 18

1.3 Thesis Structure and Aims 20

Chapter Two - Fieldwork and DNA Preparation 22-28

2.1 Field Sites and Sampling Logistics 23

vi

2.1.1 Field sites 23

2.1.2 Sampling effort 23

2.2 DNA Collection and Extraction 26

2.2.1 Toe-clipping strategy 26

2.2.2 Storage of tissue samples 26

2.2.3 DNA extraction protocol 26

2.2.4 Other methods used 27

2.2.5 Storage of extracted DNA samples 28

Chapter Three - Spatial Analyses of Abundance and Distribution 29-55

3.1 Introduction 29

3.2 Methods 32

3.2.1 Location and count data for frog populations 32

3.2.2 GIS layers and analyses 35

3.2.3 OpenModeller analyses 35

3.2.4 ArcGIS analyses 37

3.3 Results 38

3.3.1 Spatial analyses of frog distribution and abundance data 38

3.3.2 Spatial analyses of Species Distribution Models (SDMs) 40

3.4 Discussion 41

3.4.1 Broad-scale habitat preferences indicated by ArcGIS 41

3.4.2 Species distribution modelling for the Fiji Frogs 46

Chapter Four - Mitochondrial Gene Order and Evolution 56-82

4.1 Introduction 57

4.2 Methods 59

4.2.1 Sequencing of mitochondrial genomes of Fiji frogs 59

4.2.2 Long Range PCR and ABI3730 sequencing 59

4.2.3 Illumina sequencing of three frog genomes 59

4.2.4 Taxon sampling from GenBank genome sequences 61

4.2.5 Sequence alignments and data partitions 61

4.2.6 Phylogenetic reconstruction 62

4.2.6.1 PHYML trees 62

4.2.6.2 Divergence time estimates 62

vii

4.3 Results 63

4.3.1 Mitochondrial gene order in Fijian frogs 63

4.3.2 Phylogenetic relationships recovered 63

4.3.3 Molecular evolution of Neobatrachian mitochondrial

genomes 72

4.3.4 Divergence time estimates for Fijian Frogs 72

4.4 Discussion 73

4.4.1 Molecular evolution and phylogeny of anuran mitogenomes 73

4.4.2 Phylogenetic reconstruction with anuran mitogenomes 77

4.4.3 Taxonomic implications from sequence analyses 78

4.4.4 Divergence of Cornufer spp. based on mitogenome sequences 79

Chapter Five - Phylogenetics and Population Structure 83-120

5.1Introduction 84

5.2 Methods 87

5.2.1 Mitochondrial marker development and sequencing 87

5.2.2 Nuclear markers obtained from reduced representation 87

Illumina sequencing

5.2.3 Alignments, splitsgraphs and model determination 88

5.2.4 Maximum Likelihood analyses 91

5.2.5 BEAST analyses 91

5.3 Results 92

5.3.1 Phylogeographic structure in 12SrRNA and Cytb

genes of Fijian Ceratobatrachids 92

5.3.2 Phylogeographic structure of novel nuclear markers

in Fijian Ceratobatrachids 93

5.3.3 Phylogenetic Diversity (PD) 101

5.3.4 BEAST statistical analyses 112

5.4 Discussion 111

5.4.1 Cornufer vitianus (Taveuni) 111

5.4.2 Hybridisation between Fijian frogs 118

Chapter Six - Implications for Conservation of the Fijian Frogs 121-133

6.1 How special are the Fiji frogs? 122

viii

6.2 How best to apply the outcomes of the GIS analyses? 122

6.2.1 Species Distribution Models (SDMs) 122

6.2.2 Habitat management 124

6.3 Can inferences of population history inform conservation efforts? 125

6.3.1 Clues from the past: utilising the information on population

connectivity 125

6.4 Investigating the adaptive potential of Fijian Ceratobatrachids 127

6.4.1The future potential of high throughput sequencing

technology 129

6.4.2 Hybridisation – adaption or threat? 130

6.4.3 Future directions 131

Bibliography 135-162

Appendices 163-168

Appendix A - Mitochondrial genome accession details for 48 frog 164

mitogenomes used in phylogenetic study

Appendix B - Consensus network of alternative tree topologies

inferred by jModelTest for the evolution of the concatenated

protein coding genes from the mitochondrial genomes 166

Appendix C - Consensus network of alternative tree topologies

inferred by jModelTest for the evolution of the concatenated

RNA from the mitochondrial genomes of 47 frog taxa 168

ix

List of Figures

Figure 1.1 Distribution of Cornufer species throughout the genus’ range 4

Figure 1.2 The ‘Asian Origins’ model of Noble (1961) 5

Figure 1.3 The ‘Reverse Asian Origins’ model of Kuramoto (1985) 6

Figure 1.4 The ‘Papuan Progenitor’ model (Allison 1996) 7

Figure 1.5 Distribution of Cornufer vitiensis and C. vitianus 8

Figure 1.6 Cornufer vitianus, the Fiji Ground frog 9

Figure 1.7 Cornufer vitiensis, the Fiji tree frog 12

Figure 3.1 Frog populations on the six islands surveyed graphed against

precipitation 33

Figure 3.2 Spatial analysis maps showing the influence of environmental

variables 42

Figure 3.3 Consensus maps generated by ArcMap using SDMs 44-45

Figure 4.1 Mitochondrial genome organisation for the three Fijian frog taxa 65

Figure 4.2a Consensus network of 100 bootstrap trees of the concatenated

protein coding genes dataset 68

Figure 4.2b Phylogram of optimal PhyML tree for the concatenated protein coding

genes dataset 69

Figure 4.3a Consensus network of 100 bootstrap trees of the concatenated RNA

dataset 70

Figure 4.3b Phylogram of optimal PhyML tree for the concatenated RNA dataset 71

Figure 4.4a Dated BEAST chronogram of the concatenated protein coding genes

dataset 74

Figure 4.4b Dated BEAST chronogram of the concatenated RNA dataset 75

Figure 5.1a Consensus network of splits based on alignment of 12SrRNA

Sequences 94

Figure 5.1b Optimal ML tree based on alignment of 12SrRNA sequences 95

Figure 5.2a Consensus network of splits based on alignment of cytb sequences 96

Figure 5.2b Optimal ML tree based on alignment of cytb sequences 97

Figure 5.3a Consensus network of splits based on concatenated cytb/12SrRNA 98

Figure 5.3b Optimal ML tree based on concatenated cytb and 12SrRNA

sequences 99

Figure 5.3c Consensus network of 100 bootstrap trees for concatenated

x

cytb+12S 100

Figure 5.4a Consensus network of splits based on alignment of nuc5 sequences 103

Figure 5.4b Optimal ML tree based on alignment of nuc5 sequences 104

Figure 5.5a Consensus network of splits based on alignment of nuc8_1 and

nuc8_2 105

Figure 5.5b Optimal ML tree based on alignment of nuc8_1 and nuc8_2 106

Figure 5.6a Consensus network of splits based on alignment of nuc11_1 107

Figure 5.6b Optimal ML tree based on alignment of nuc11_1 108

Figure 5.6c Consensus network of splits based on alignment of nuc11_1 109

Figure 5.6d Optimal ML tree based on alignment of nuc11_1 110

Figure 5.7a BEAST chronogram dated on HPD lower probability estimate 115

Figure 5.7b BEAST chronogram dated on HPD upper probability estimate 116

xi

List of Tables

Table 2.1 Descriptions of the island sites surveyed for presence of Fiji

Cornufer 24-25

Table 3.1 Habitat codes for quantitative analyses in ArcMap 34

Table 3.2 BioClim data for sampled populations of Fijian Cornufer 36

Table 3.3 OpenModeller (Version1.1.0) SDM algorithms tested against Fijian

Cornufer spp. 43

Table 4.1 Universal and species-specific primers used to amplify mitogenomes 60

Table 4.2a Optimal models for individual genes and concatenated datasets 66

Table 4.2b Phylogenetic diversity of Neobatrachians in PhyML Trees 67

Table 4.3 Highest Posterior Density (HPD) Values from BEAST 2.0 76

Table 5.1 Population dataset used in phylogenetic analyses 90

Table 5.2a Phylogenetic diversity estimates from two mitochondrial and

three nuclear markers 112

Table 5.2b Phylogenetic diversity estimates from optimal ML trees of

C. vitianus and C. vitiensis island populations. 113

Table 5.3 Ancestral location probabilities for island populations from

BEAST 2.0 114

1

CHAPTER ONE

GENERAL INTRODUCTION

2

1.1 GENERAL INTRODUCTION

The order Anura, also called Salientia or frogs, is one of three major orders of

the subclass Lissamphibia, class Amphibia (Caudata and Gymnophiona being the

other two); in which there are approximately 6,509 extant species (AmphibiaWeb

2015). The order Anura was generally divided into three clades Archaeobatrachia,

Neobatrachia, and Mesobatrachia, but these older groupings are being reviewed

using molecular data (Gissi et al. 2006a; Pyron and Wiens 2011; Zhang et al. 2013).

The Fijian frogs are now described within the genus Cornufer (sub-genus Cornufer),

which belongs to the recently revised frog family Ceratobatrachidae (Brown et al.

2015). It is the most diverse of the six taxonomically recognized genera in the family

with ~90% of the 90+ species in the family, and is the most widespread (Brown Pers.

Comm. 2015).

1.2 THE CERATOBATRACHIDS OF FIJI

1.1.2 Cornufer in the Pacific

The genus of Cornufer currently includes ~41 known species, although the

species tally is increasing as more field work in the Indo-Pacific and Melanesian

regions progresses (Brown and Richards 2008; Foufopoulos et al. 2004; Brown et al.

2013; Richards et al. 2014). It has undergone taxonomic revision only recently

(Brown et al. 2015), and all species within Cornufer were once part of Platymantis

(now reduced to only the Phillipine Island taxa). The distribution of Cornufer ranges

from Papua New Guinea to the Fiji Islands, covering an approximate geographical

area of 0.5 million km² in the Pacific Ocean (Figure 1.1). Cornufer is of current

taxonomic interest as several species and species groups within the genus are being

reviewed using molecular tools, and genetically distinct taxa are emerging from these

studies (Siler et al. 2009). Additionally, congeners exhibit a bewildering array of

morphologies and ecologies, which implies much genotypic variation (Brown 2009;

Brown et al. 2015). The historical biogeography of Cornufer is complex and of

intense interest for amphibian biologists since it was described and over time as new

species have been added (Boulenger 1884, 1918; Noble 1931; Tyler 1979; Bossuyt et

al. 2006; Wiens et al. 2009).

There are three main hypothetical routes for the colonisation and subsequent

establishment of Ceratobatrachid lineages on islands from Southeast Asia to the

3

Fijian archipelago. The first hypothesis (Noble 1961; articulated in Brown 2004)

suggests that a radiation of Ceratobatrachids occurred in the Philippines (derived

from an Asian source), followed by dispersal west through the Melanesian group to

Fiji and north to Palau, this is known as the ‘Asian Origins’ model (Figure 1.2). The

second model is essentially a reversal of the first, modelling a backward dispersal

route to the Philippines following radiation within the island world stretching from

New Guinea to the Solomons (Figure 1.3). This ‘Reverse Asian Origins’ construct

was initially proposed by Kuramoto (1985; articulated in Brown 2004).

The third and final scenario, termed the ‘Papuan Progenitor’ hypothesis

(Brown 2004) describes two parallel dispersal routes, one traversing east from the

Papuan source area towards the Philippines, and the other westwards to Fiji (Figure

1.4). The Papuan progenitor species are suggested to have evolved in isolation on

former landmasses that collided with and accreted to the north coast of New Guinea

(Hilde et al. 1976; Yan and Kroenke, 1993; Allison 1996; Hall, 1996). Though

thoroughly debated and supported by various proponents, no single construct has

emerged as the most likely geographic origin (Brown 2004). What is clear, however,

is that the evolutionary history of the genus Cornufer is complex and will require a

multi-disciplinary approach to resolve biogeographic origins of the clade (see Brown

et al. 2015). For now, the focus is on within-archipelago histories, the resulting

models of diversification among congeners can be used to understand the

evolutionary history of this enigmatic and diverse clade of Pacific Island amphibians.

1.1.2 The Fiji ground frog, Cornufer vitianus

Cornufer vitianus is found in primary lowland to highland rainforest,

secondary re-growth forests, plantations, and coastal littoral forest with relatively

moderate disturbance levels (Osborne et al. 2013). It occupies more mesic habitats

than C. vitiensis, and unlike the tree frog can often be found in brackish habitats

(Kuruyawa et al. 2004). This lack of habitat selectivity would make it less

vulnerable to forest reduction on the smaller islands in its range than C. vitiensis.

Individuals of C. vitianus are primarily ground-dwelling, although smaller

individuals are often found on foliage less than three metres off the ground (ibid.).

They hide in earthen burrows or rotting plant material during the day (Gorham 1971;

Narayan et al. 2008).

4

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10

Platymantis vitianus (Cornufer vitianus) is considered endangered (EN

B1ab[v]) under the IUCN classification system (IUCN 2014). Museum records of

Cornufer vitianus suggest that it was once present on the largest island in the Fiji

group, Viti Levu (Gorham 1965). The species is currently known to persist on six

islands: Viti Levu, Vanua Levu, Taveuni, Gau, Ovalau, and Viwa (Figure 1.5).

Combined, this makes up a landmass of 6261.1 km², of which approximately 44.6%

(2792.05 km²) is forested. Cornufer vitianus was thought to have been extirpated

from Viti Levu and Vanua Levu by a combination of factors including predation by

the small Indian mongoose (Herpestes javanicus), rats (Rattus spp.), the cane toad

(Bufo marinus) and modification of its forest habitat. However, a survey in 2004

resulted in the “rediscovery” of Vanua Levu C. vitianus populations (Morrison et al.

2004). Then in 2009, a remnant population of C. vitianus was “rediscovered” in

northern Viti Levu in the Nakauvadra Range during a BIORAP survey of the area

(Thomas 2009).

Cornufer (subgenus Cornufer) vitianus is larger than C. vitiensis with females

growing to snout-urostyle lengths (SUL) of 116 mm, weighing up to 170 g (Figure

1.6). These very large females are most common on the islands of Viwa and Gau

(Kuruyawa et al. 2004). Males are generally much smaller. Colouration is less

variable than in C. vitiensis however certain island populations contain highly

variable colour morphs (Pers. obs.). Cornufer vitianus (Platymantis vitianus) is

nocturnally active and can often be found at night sitting on the ground in the forest

or on banks of forest streams waiting to ambush insect prey. Very often, smaller

sized individuals are found on the branches and leaves of riparian shrubs that are

flowering or fruiting (Pers. obs.). Fiji ground frogs can produce eggs year-round

(Morrison 2003), although most breeding activity is thought to occur during the wet

season from November to April (Thomas 2007). Both sexes call and it is has been

suggested that the female advertises for the male frog, however, advertisement by the

male is still a possibility (Bishop Pers. comm., 2005). Cornufer (Platymantis)

vitianus is a terrestrial breeder with direct development in large yolky eggs (~40

eggs), which are laid in low-lying locations in moist substrates (Narayan et al. 2008).

Eggs hatch after an interval of approximately four weeks.

11

1.1.3 The Fiji tree frog, Cornufer vitiensis

Cornufer (Platymantis) vitiensis inhabits primary lowland and highland

rainforest as well as semi-disturbed vegetation, such as plantations of mahogany

(Gorham 1968; Morrison 2003). They are less common in mesic habitats with high

levels of human activity (Osborne et al. 2008). Individuals are often found within or

perched upon Pandanus plants (Gorham 1971; Osborne et al. 2008). Other plants in

which tree frogs have been found during nocturnal surveys are on banana (Musa

spp.) leaves, on Syzygium saplings, in birds’ nest ferns (Asplenium nidus), epiphytic

ferns, and on streamside vegetation such as ground ferns and Acalypha rivularis

(ibid.).

The ecology and reproductive biology of C. vitiensis has been studied more

fully than C. vitianus (Gorham 1971; Gibbons and Guinea 1983; Morrison 2003),

probably due to the accessibility of populations close to Suva. Cornufer vitiensis

adults range from 22-60 mm in SUL, and metamorphs range between 6-16 mm

(Osborne et al. 2008). Cornufer vitiensis finger discs are larger than toe discs, with

the third finger disc being roughly equal in size to the individual’s eye, ranging from

one to four millimetres (Morrison 2003; Figure 1.7). Tree frogs are very variable in

colour, with dark brown-green, yellow-green, and reddish or bright orange morphs,

often with markings such as a medial dorsal cream stripe or darker stippling in the

shape of an ‘x’. Ryan (1984) identified 22 common colour morphs and 17 rare

colour patterns; however this is likely an underestimate of the diversity. The ventral

surface often has less distinctive colouration and patterning, and is generally pale

yellow-green.

Cornufer vitiensis breeds throughout the year but is more reproductively active

between August and November, during the transitional period from the ‘wet’ to the

‘dry’ season (Osborne et al. 2008). Like the ground frog, both male and female C.

vitiensis call (Boistel and Sueur, 1997). The call is likened to the sound of a

'dripping tap', and is generally heard more frequently during the breeding season

(Morrison Pers. comm. 2004). Eggs are laid at the base of leaves of Pandanus, lilies

and epiphytic ferns (Morrison 2003). Clutch heights may vary, but are generally one

to two metres above the ground and are often located close to a small stream.

Clutches are relatively small (30 – 40 eggs) as the eggs are quite large (7 – 9 mm

wide) to sustain direct development within the egg (Ryan 1984). Hatchlings emerge

after 4 – 5 weeks (Gibbons and Guinea 1983).

12

Figure 1.7 Cornufer vitiensis, the Fiji tree frog (Girard) NT

13

1.1.4 The taxonomic status of the Fiji frogs

The two Fiji frogs represent the eastern-most limit of the range of the family

Ceratobatrachidae and the genus Cornufer (subgenus Cornufer). Recent genetic

analysis points to a common ancestor for the Fiji frogs, which may have originated

from the Bismarck Archipelago (Brown et al. 2015). Little is known about how this

ancestor got to the Fiji group, although several theories have been suggested (Allison

1996). The two most widely published hypotheses are that the founding population

of this ancestor either rafted to Fiji on floating vegetation, or was brought to Fiji as a

food item for humans (Ryan 2000). It may be possible that an extinct giant frog

fossil discovered during an archaeological cave excavation (Worthy 2001) is the

ancestor of Fiji Ceratobatrachids. However, this is unlikely as cave deposits

contained all three species in the same layer, suggesting that the larger Cornufer

(Platymantis) megabotovitiensis was one of three lineages present prior to humans

arriving in Fiji. The ‘megaboto’ lineage did not persist, perhaps due to predation by

humans and/or introduced predator species like the Pacific rat (Rattus exulans).

1.2 MOLECULAR SYSTEMATICS OF ANURANS

1.2.1 Evolutionary relationships, molecular taxonomy, and historical biogeography

Most genetic information to date for animal taxa has been obtained from the

mitochondrial genome. DNA sequencing has developed over the last four decades,

and the majority of phylogenetic studies have utilised mitochondrial genes although

it is becoming increasingly more common for standard phylogenetic analyses to use

multiple independent loci, sometimes even 10 – 20 or more nuclear genes (Simon et

al. 2006; Yang and Rannala 2012).

The convenient and utilitarian nature of mitochondrial DNA (mtDNA) in

phylogenetic research on animals has been due to several characteristics of the

genome: (a) a compact gene order arrangement with few intergenic spaces and

introns (Boore and Brown 1998); (b) an absence of evidence for widespread

recombination (Barr et al. 2005); (c) Maternal inheritance usable in tracing ancestral

relationships (Avise et al. 1987); (d) multiple copies of cell organelles increasing

amplification success (Kocher et al. 1989); (e) a conserved simple structure

(Wolstenholme 1992); (f) a high mutation rate in non-conserved regions of the

mtDNA genome, up to 10 times faster than the nuclear DNA in animals (Brown et

al. 1979; Zheng et al. 2006); (g) low effective population size of mitochondrial DNA

14

alleles (Avise et al. 1988); and (h) higher resolution provided by the faster evolving

mtgenome enables the mapping of adaptations onto phylogenies (with shorter branch

lengths) that have been reconstructed using mtDNA (Moore 1995).

The order Anura comprises approximately 88% of the 7384 species of

living amphibians (AmphibiaWeb 2015). The majority of genetic sequences

available for Anura are for the gene region that codes for the larger and smaller

ribosomal (RNA) sub-units (12S and 16S). Other common markers include the gene

region coding for the cytochrome b (cytb) apoenzyme, genes that code for the three

cytochrome oxidase subunits (COI-II), and those that code for the NADH

dehydrogenase subunits (ND1-6) (Boore 1999).

With the publication of complete mitochondrial genomes for anuran taxa,

primer design and the choice of what markers to use in phylogenetic research has

become much more tractable (Mueller 2006). The non-coding ‘control region’ was

of particular interest in the last decade, as these sequences are highly variable

between individuals and therefore of great use in population genetic studies (Pereira

et al. 2004). In particular, the ‘D-loop’ region has been used in several population

genetics studies (e.g. Monsen and Blouin 2003). The hypervariability of this section

of the control region make it a useful tool for research into the population genetics of

anurans, although few published studies exist. Nuclear markers became more popular

in population genetics in the mid-2000s (Beebee 2005) with most population genetics

studies determining microsatellite profiles for populations.

As molecular techniques have advanced considerably, the single copy status

of the nuclear genome has become less of a problem limiting amplification success.

In addition, introns in the nuclear genome are known to evolve at rates comparable to

more slowly evolving sections of the mitochondrial genome, making these markers

useful for studies of an intra-specific nature (Mathee et al. 2007). Most phylogenetic

research on anuran taxa today incorporates markers from both the nuclear and the

mitochondrial genomes. The most commonly used nuclear DNA (nDNA) markers

are the protein coding regions Rag-1, Rag-2, Rag-3 and the rhodopsin. Other

markers include the coding regions for 18SrRNA, tyrosinase, c-myc, 5.8S, 28S,

RNase P RNA, and B-Fibrinogen. However, by far the most commonly used nuclear

markers for intra-specific research like that in population genetics are nuclear

microsatellites, which have extremely high mutation rates and are considered

‘neutral’ markers (Miesfeld et al. 1981; Tautz 1989).

15

Historical biogeography is a discipline that seeks to explain the geographic

distribution of biological taxa in terms of processes that occur over evolutionary

time-scales (Crisci 2001). The most common factors that have shaped the

geographic distribution of genealogies are changes in climate and geomorphologic

change, which have provided the impetus for processes such as vicariance, dispersal,

speciation and extinction (de Queiroz 2007). Phylogeography is the combination of

classic biogeographic theory with phylogenetic information. Phylogeographic

studies interpret the geographical distribution of intra-specific lineages (based on

gene trees) with a clear emphasis on historical factors that affected the evolution of

genetic diversity within a species (Avise et al. 1998).

Classic phylogeographic studies are based on within-species lineages

however the growing body of ‘comparative phylogeography’ work incorporates

information from across-species lineages (Bermingham and Moritz 1998).

Comparative phylogeographic studies contribute to the understanding of how local

and regional biotic community structure has been shaped by evolutionary forces

(Arbogast and Kenagy 2001). Schneider et al. (1998) utilized this approach to

explore patterns of distribution of tropical rainforest herpetofauna (three lizard and

three anuran species). Their results suggest that species diversity and distribution in

the wet tropics of the Australian sub-continent are largely shaped by climatic-

induced extinction and re-colonization processes.

Limitations to interpreting gene trees in both classic and comparative

phylogeography led to the emergence of ‘statistical phylogeography’, which tests

phylogeographic scenarios by incorporating demographic parameters (Knowles and

Maddison 2006). Statistical phylogeography is better suited to account for the

problems of stochasticity inherent in genetic processes and the complexity of a

species evolutionary history than traditional phylogeographic studies (Knowles

2009). One of the main pitfalls of a non-statistical approach was the lack of

validation of the error value of an inferred phylogeographic model (Knowles and

Maddison 2006); e.g. this was a major critique of Templeton’s nested clade analysis

(NCA) method (Templeton 2004), in addition to other criticisms.

The main use of phylogeographic analyses in anuran research has been to

interpret past patterns of distribution in relation to current patterns. Factors such as

fragmentation, extinction, re-colonization, gene flow, habitat reduction, climatic

cycles and geomorphologic events have resulted in range shifts and the production of

16

current genetic patterns. Climatic induced range expansion and/or contraction is a

recurrent theme in the literature. Many studies have demonstrated how glacial or

interglacial cycles have influenced anuran population histories (e.g. Schneider et al.

1998; Austin et al. 2004; Hoffman and Blouin 2004; Snell et al. 2005; Edwards et al.

2007). Other phylogeographic interpretations of genetic distribution suggest that

vicariant or dispersal events are the main influences shaping gene tree topologies

(Nielsen et al. 2001; Evans et al. 2003; Vences et al. 2003; Roelants and Bossuyt

2005; Mulcahy et al. 2006; de Queiroz 2007).

1.2.2 Use of Genetics in the Conservation of Endangered Anurans

1.2.2.1 Mitochondrial and nuclear markers used in phylogeography

Understanding population dynamics of amphibian taxa is of considerable

importance in light of the current trend of global declines. Information on the

genetic connectivity of populations, population substructure, and external factors (in

the landscape) shaping population histories are all essential for identifying agents of

decline (Moritz 2002). Habitat loss and fragmentation have been implicated in the

majority of studies of anuran species (Stuart et al. 2004). Landscape genetics is an

effective tool for understanding how habitat variables affect genetic structure and

diversity of a species of concern. It is even more applicable when the species of

concern has a widespread but disjunct distribution within its geographical range

(Beebee 2005; Stevens et al. 2006), as is the case for the Fiji Ceratobatrachids.

The global decline in amphibian species first highlighted in 1989 during the

first world congress on herpetology created an international impetus into research on

the causes and consequences of these declines (Blaustein and Wake 1990). A review

of this research in 2003 (Storfer 2003) noted the valuable contribution that molecular

ecology can have for such studies. Population histories of endangered or declining

species can be inferred from the genetic makeup of populations. Events such as

fragmentation, bottlenecks and hybridisation can be identified, and the information

about the past demographic history can be used to determine population trends.

Other possible outcomes from molecular research include an estimation of the

effective population size, the genetic diversity within a population, and/or the degree

of inbreeding that may be taking place in a population of interest. In addition,

genomic approaches can be used to investigate ‘adaptive genetic variation’, a hot

topic amongst conservation geneticists (Nielsen 2005).

17

There are three main areas of interest within the broad field of population

genetics that have been explored by anuran biologists. Firstly, the estimation of

effective population size (Ne) and diversity (Beebee 2005). Effective population size

is considered a more important parameter to estimate than census size in wild

populations as it is more indicative of the probability of persistence (Funk et al.

1999). Genetic diversity is usually proportional to effective population size (Miller

and Waits 2003) although this is not always the case in anuran populations (Burns et

al. 2004). Diversity is expected to be lower in smaller populations as the degree of

inbreeding is expected to be higher (Hedrick 2001). There have been few studies

that have investigated Ne in anuran species (Schmeller and Merila 2007); this is

concerning as Ne estimates have great potential for predicting the viability of a

population when long-term census data is non-existent (Storfer 2003). Population

declines can be inferred from genetic population size and variability data (Collins

and Storfer 2003; Beebee 2005). These are important tools for anuran biologists

studying species that have complicated population histories (Burns et al. 2004;

Hoffman and Blouin 2004).

The second area of interest in the population genetics of anurans is the

investigation of genetic structure and/or substructure. Studies of this nature often

explore dispersal (Palo et al. 2004), gene flow (Barber 1999) and genetic

connectivity (Burns et al. 2004). Nested clade phylogeographic analyses (NCPA)

have been used for this purpose, because it has potential application to differentiate

between current and historic gene flow (Templeton 1998). However, there is still

much debate about the statistical validity of the results of NCPA results (Knowles

2004; Knowles and Maddison 2006), and in general there are a number of competing

methodologies for analysing population genetic structure and also inferring

demographic history from sequence data (e.g. Pritchard et al. 2000). Molecular

estimates of gene flow have most commonly been determined by calculating FST,

which is an estimate of the degree of genetic differentiation (allelic frequencies)

between population pairs (Weir and Cockerham 1984). The value of FST can be used

to estimate dispersal between populations (Palo et al., 2004).

Thirdly, dispersal rates are an important parameter controlling the degree to

which sub-populations function independently in an area (Palo et al. 2004b), a

mechanism of genetic connectivity in anuran populations. Sex-specific differences

in the dispersal of anuran species have also been investigated using molecular tools

18

(Austin et al. 2004; Palo et al. 2004a). One aspect of the genetic structure of

declining anuran populations that has been investigated are fragmentation events. In

these studies, FST values and the genetic distance amongst populations (Nei’s genetic

distance is a popular measure of genetic divergence) have been used to determine the

degree of population subdivision. In this work, microsatellites have been the most

commonly employed markers for identifying fragmentation of declining species (Vos

et al. 2001; Monsen and Blouin 2003; Funk et al. 2005).

Hybrid populations have a unique genetic structure, and although

hybridisation between anuran species has been considered rare it has been inferred

following admixture of two previously allopatric populations (Espinoza and Noor,

2002). The outcomes of hybridisation can be unclear (Abbott et al. 2013). In some

cases it is thought that hybridisation might compromise the genetic integrity of an

endemic or native anuran, as in the case of Rana ridibunda in central Europe

(Vorburger and Reyer 2003). In some cases, hybrid populations might also

accumulate deleterious mutations and affect viability of offspring (Guex et al. 2002).

Conversely, hybrid offspring can also have greater reproductive success in disturbed

environments (Allendorf et al. 2014).

Hybridisation has also been seen by some as a potentially important

mechanism for generating phenotypic variation in colour morphs of poison frogs

(Dendrobatidae), and increasingly researchers are suggesting that hybridisation has

important evolutionary significance for generating phenotypic novelty (e.g. Abbot et

al. 2013; Becker et al. 2013). Developing a better understanding of the positive and

negative outcomes of hybridisation is an important challenge of our time as it

impacts our ability to predict biodiversity response to environmental change, and in

particular global warming (Abbott et al. 2013; Becker et al. 2013; Allendorf et al.

2014).

1.2.2.2 Phylogeographic analyses: tools to discern population history and

connectivity

Phylogeographic interpretations of genetic data are increasingly being used to

infer patterns of population history in threatened anuran populations. There are

several ways in which phylogeographic analyses can be undertaken and utilised for

conservation purposes (Bloomquist et al. 2010). Past patterns of range expansion

and contraction in populations of the threatened Columbia Spotted Frog (Rana

19

luteiventris) were determined from nested clade and networking analyses (Bos and

Sites 2001). The authors recommended that a genetically unique population be

managed independently of the other remaining populations, and that translocations

between distant populations be avoided. It was suggested that estimates of gene flow

between populations of an endangered species (i.e. genetic connectivity of

populations) be used to make management decisions. A study by Vieites et al.

(2006) revealed a low level of haplotype sharing between populations of Mantella

bernhardi, a threatened anuran that was commonly exploited in the pet trade. The

low gene flow between populations prompted the authors to designate two very

genetically distinct populations in the North and South of the species range, as ideal

units for conservation efforts.

A ‘complex history of (genetic) connectivity’ was detected in Dendrobates

tectorius, an endemic anuran found in the Guianan Shield in South America (Noonal

and Gaucher 2006). To prevent human population expansion in these areas from

reducing genetic connectivity and diversity in these areas, it was recommended that

conservation efforts for this species should focus on parts of the coastal range of the

species. A comparative phylogeographic analysis that included two threatened

anuran species, Litoria nannotis and L. rheocola, revealed a history of climate-

induced vicariant events in the Wet tropical rainforests of Eastern Australia

(Schneider et al. 1998). These results provided a framework for investigating the

current perceived decline of these threatened frog species in their range.

The phylogeographic study of a threatened species of frog (Rana draytonii)

detected a zone of genetic overlap with the non-threatened species R. aurora, which

would require a review of the conservation status of the species (Shaffer et al. 2004).

The authors also suggested that areas where R. draytonii had very small populations

may benefit by translocating individuals from a closely related population in another

area. A congener R. lessonae, the pool frog, is widely distributed throughout the

eastern parts of the European continent. It was thought to have been introduced to

Britain from Italy however a recent phylogeographic study showed that the Norfolk

population in Western Britain is actually native to this area (Snell et al. 2005). This

study prompted the initiation of a re-introduction programme of Pool Frogs from

Northern Europe to Norfolk.

The above examples of recent findings typify the important contributions

made by phylogeographic investigations of endangered anuran populations.

20

Conservation management is enhanced by recommendations based on the genetic

diversity and structure of populations or species. There is often the argument over

what aspects of genetic diversity are best to conserve (next section). However, in

general by identifying populations or areas where as much of evolutionary potential

of a species is encapsulated by the total genomic makeup of all individuals, anuran

biologists can reasonably ensure conservation efforts are most effective for the

persistence of the population/species. More recently, “Bayesian Phylogeography”

(Lemey et al. 2009), which seeks to reconstruct the ancestral location of individuals

within a rooted, time-measured phylogeny, is fast becoming one of the most popular

approaches for inferring demographic histories. A reason for this is that it explicitly

models the direction of species range expansion and takes into account uncertainty of

phylogenetic inference from available data (Bloomquist et al. 2010).

1.3 Thesis Structure and Aims

The aims of this study was to: i) examine the distribution, habitat and genetic

structure of Fijian ground and tree frogs; and, ii) evaluate how this information can

be used for conservation planning in Fiji.

Overall objectives were to:

� Conduct a survey of ground and tree frog distributions in the Fijian Islands

� Investigate the potential of using an ArcGIS approach to describe habitat of

Fijian Cornufer and to provide a context for interpreting genetic analyses;

� To use high throughput sequencing with the Illumina platform to characterise

the mitogenomes of Fijian frogs and also obtain novel nuclear markers that

might be used for making inferences of population structure and

phylogeography

� To characterise, by ABI 377 Sanger sequencing, genetic variation of

candidate gene loci (mitochondrial and nuclear genes) in DNAs of Fijian

ground and tree frogs, and use this information to investigate genetic

structure and population history of Fijian frogs

� To synthesize the spatial and genetic information to direct conservation

efforts for the Fijian frogs

21

Chapter 1 of this thesis reviews the literature concerning Cornufer in the Pacific,

before focussing on the Fiji playtmantids. All relevant background information to

the major components of this study is then discussed in detail. Chapter 2 details the

generic field sampling, frog processing and DNA extraction protocols used to

generate data for the successive chapters. In Chapter 3, I describe the GIS

modelling and analyses of the distribution and count data of Fijian frogs collated

during field surveys to collect the genetic samples.

Chapter 4 describes mitochondrial genome sequencing using the Illumina

sequencing platform and phylogenetic analyses of these data in the context of

published Batrachian and Neobatrachian frog mitogenomes. Chapter 5 reports novel

nuclear markers developed using a reduced representation Illumina sequencing

protocol. The analyses in this chapter examine the distinctiveness of allelic variation

in different island populations and contrast the genetic structure and histories of

ground and tree frogs. The final chapter, Chapter 6, collates all the results of this

study and identifies important points for consideration in current and future

conservation and population management strategies. It ends with a brief introduction

to avenues for continuing research with regard to the use of genetic and GIS tools.

22

Chapter Two

Fieldwork and DNA Preparation

23

2.1 FIELD SITES AND SAMPLING LOGISTICS

2.1.1 Field sites

In order to ensure as much of the recorded former range of the Fiji

Ceratobatrachids was studied, as many sites on the islands where frogs were

previously recorded were surveyed for extant populations. This required extensive

field work on all of the eight islands where the two species have been recorded.

Field sites were selected a priori based on the following criteria: reports of extant

frog populations in the area, proximity to primary rainforest patches, and the

presence of the land-owning unit within the nearby village (Table 2.1).

2.1.2 Sampling effort

Sampling sites were selected based on the following criteria: primary or

secondary re-growth forest, moderate to high tree density, proximity to water bodies

(i.e. streams or ponds), anecdotal reports of frog populations present, and proximity

to other areas sampled (Table 2.1). Primary rainforest sites were preferred to

secondary vegetation as populations were presumed to be greater in less disturbed

habitat (Osborne et al. 2008).

Each site was searched for two to three hours at night by a sampling team of

four to five individuals. The sampling team usually consisted of seven individuals,

spread out over a greater area to maximize the chances of capturing frogs, where the

local frog population was thought to be scarce and difficult to encounter. Searchers

looked in vegetation, leaf litter and along stream banks for either species. Where

both species were found in sympatric populations, some searchers focussed efforts

on the arboreal congener C. vitiensis, while others searched for the ground-dwelling

C. vitianus species. Frogs were caught by hand and placed in click-seal plastic bags

for processing at the end of the search. All the captured individuals were processed

by the principal researcher to standardise the bias in observer error.

The body weights of all frogs were measured on a Pesola scale to the nearest

tenth of a gram. Body length was measured as snout-urostyle length (SUL) in

millimetres using a Vernier calliper. Morphometric and habitat information (perch

plant and height) for captured frogs were either recorded using a PDA (weather

permitting) or a waterproof notebook.

24

T

able

2.1

Des

crip

tions

of t

he Is

land

Site

s Sur

veye

d fo

r Pre

senc

e of

Fiji

Cor

nufe

r.

Isla

nd

Site

H

abita

t C

anop

y C

over

D

istu

rban

ce

Stre

am

Wid

th (m

) Fr

og S

peci

es

Viw

a N

auru

ru

1 >9

0%

40-6

0%

0.0

C. v

itian

us

Viw

a To

vuni

4

20-4

0%

60-8

0%

0.0

C. v

itian

us

Viw

a N

aivi

tuka

3

<20%

>8

0%

0.0

C. v

itian

us

Ova

lau

Dam

u 2

20-4

0%

>80%

0.

0 C

. viti

anus

O

vala

u N

aika

tini

6 40

-60%

40

-60%

3.

0 C

. viti

anus

O

vala

u Lo

ru

11

>90%

<2

0%

0.0

C. v

itian

us

Ova

lau

Kor

omak

awa

6 40

-60%

60

-80%

2.

0 C

. viti

anus

O

vala

u G

usun

iwai

6

>90%

<2

0%

3.0

C. v

itian

us

Ova

lau

Dak

uina

mar

a 6

40-6

0%

60-8

0%

0.0

C. v

itian

us

Ova

lau

Nam

alat

a 11

>9

0%

<20%

4.

0 C

. viti

anus

Ta

veun

i Ta

voro

6

40-6

0%

20-4

0%

3.0

C. v

itian

us

Tave

uni

Wai

nise

rei

1 20

-40%

20

-40%

4.

0 C

. viti

anus

Ta

veun

i Tu

a 8

40-6

0%

<20%

2.

0 C

. viti

anus

Ta

veun

i Q

elen

i Ck

7 20

-40%

20

-40%

3.

0 C

. viti

anus

Ta

veun

i So

love

6

20-4

0%

>80%

2.

0 C

. viti

anus

Ta

veun

i Lo

mal

agi

9 >9

0%

<20%

1.

0 C

. viti

anus

Ta

veun

i Ta

vuya

go

8 20

-40%

40

-60%

0.

0 C

. viti

anus

Ta

veun

i R

avile

vu R

eser

ve

9 >9

0%

<20%

0.

0 C

. viti

anus

V

anua

Lev

u N

adi-i

-cak

e 11

80

%

20-4

0%

0.0

C. v

itien

sis

Van

ua L

evu

Dev

odam

udam

u 11

80

%

<20%

2.

0 C

. viti

ensi

s V

anua

Lev

u D

riti

6 >9

0%

<20%

4.

0 C

. viti

ensi

s V

anua

Lev

u N

asea

levu

6

80%

40

-60%

3.

0 C

. viti

ensi

s V

anua

Lev

u V

euku

7

40-6

0%

40-6

0%

5.0

C. v

itien

sis

Van

ua L

evu

Nai

lusi

6

40-6

0%

60-8

0%

4.0

C. v

itien

sis

Van

ua L

evu

Wai

sali

Res

erve

11

>9

0%

<20%

5.

0 C

. viti

ensi

s V

anua

Lev

u N

auru

ru

6 20

-40%

>8

0%

2.0

C. v

itien

sis

Van

ua L

evu

Wai

tula

gasa

i 6

20-4

0%

40-6

0%

3.0

C. v

itien

sis

Gau

K

awak

awan

okon

oko

6 20

-40%

>8

0%

2.0

C. v

itian

us

Gau

N

abod

ua

1 20

-40%

60

-80%

3.

0 C

. viti

anus

G

au

Ivita

kala

i 1

40-6

0%

60-8

0%

4.0

C. v

itian

us

25

Tab

le 2

.1 C

ontin

ued…

Isla

nd

Site

H

abita

t C

anop

y C

over

D

istu

rban

ce

Stre

am

Wid

th (m

) Fr

og S

peci

es

Gau

N

avas

a 6

40-6

0%

60-8

0%

1.0

C. v

itian

us

Gau

N

akal

irau

6 40

-60%

40

-60%

0.

0 C

. viti

anus

G

au

Val

eibi

5

20-4

0%

>80%

4.

0 C

. viti

anus

V

iti L

evu

Nak

auva

dra

11

>90%

<2

0%

6.5

C. v

itien

sis

Viti

Lev

u N

ukus

ere

10

20-4

0%

>80%

3.

0 C

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s V

iti L

evu

Nal

idi

6 20

-40%

40

-60%

1.

0 C

. viti

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s V

iti L

evu

Wai

nam

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u 7

>90%

<2

0%

3.0

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sis

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avun

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5

20-4

0%

>80%

2.

0 C

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s V

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evu

Nad

ariv

atu

11

>90%

20

-40%

4.

0 C

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ensi

s V

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evu

Tavu

nam

asi

11

>90%

20

-40%

4.

0 C

. viti

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s V

iti L

evu

Som

usom

inau

luva

tu

11

80%

<2

0%

3.0

C. v

itien

sis

Viti

Lev

u D

evos

asa

11

>90%

40

-60%

3.

0 C

. viti

ensi

s V

iti L

evu

Dre

keti

11

>90%

40

-60%

3.

0 C

. viti

ensi

s V

iti L

evu

Lom

olom

olol

evu

10

<20%

20

-40%

5.

0 C

. viti

ensi

s V

iti L

evu

Kaw

anay

avat

o 11

<2

0%

<20%

5.

0 C

. viti

ensi

s V

iti L

evu

Wai

lam

ulev

u 11

40

-60%

40

-60%

4.

0 C

. viti

ensi

s V

iti L

evu

Wai

yasi

yasi

11

60

-80%

40

-60%

2.

0 C

. viti

ensi

s V

iti L

evu

Mat

okan

a 10

>9

0%

<20%

1.

0 C

. viti

ensi

s

Cod

e D

istu

rban

ce

Lev

el

1 <2

0%

Low

2

20-4

0%

Low

to m

oder

ate

3 40

-60%

M

oder

ate

4 60

-80%

M

oder

ate

to h

igh

5 >8

0%

Hig

h

Cod

e C

anop

y C

over

1

<20%

2

20-4

0%

3 40

-60%

4

60-8

0%

5 80

%

6 >9

0%

Cod

e H

abita

t Typ

e 1

Coa

stal

bea

ch fo

rest

2

Coa

stal

bea

ch fo

rest

and

pla

ntat

ions

3

Plan

tatio

ns

4 Pl

anta

tions

and

hum

an h

abita

tion

5 Se

cond

ary

low

land

rain

fore

st a

nd p

lant

atio

ns

6 Se

cond

ary

low

land

rain

fore

st

7 Pr

imar

y lo

wla

nd ra

info

rest

8

Seco

ndar

y m

id-h

ighl

and

rain

fore

st

9 Pr

imar

y m

id-h

ighl

and

rain

fore

st

10

Seco

ndar

y hi

ghla

nd ra

info

rest

11

Pr

imar

y hi

ghla

nd ra

info

rest

26

Frogs were only brought back to the village when the weather became too

intense to allow for accurate processing in the field. All frogs were then returned to

the site of capture.

2.2 DNA COLLECTION AND EXTRACTION

2.2.1 Toe-clipping strategy

A single digit (the third toe on the left foot) was clipped just after the first

joint) using sharp sterile scissors (Figure 2.2). The scissors were wiped clean with

95% ethanol in between each frog processed and between sampling sites (Gonser and

Collura 1996). A single digit was taken for extractions in order to minimise physical

harm to the frogs and to yield sufficient DNA for PCR. Although toe clipping is a

standard practice for amphibian research, it has been shown to affect survival,

reproduction and foraging (Arntzen et al. 1999; Davis and Ovaska 2001; McCarthy

and Parris 2004). However, as only one digit per individual was clipped there was

no accidental repetition of sampling (no frog was sampled more than once), as well

as minimizing any adverse effects on the animal (McCarthy and Parris 2004). This

method was approved by the Animal Ethics Committee for the University Research

Council in the Faculty of Science, Technology and Environment (FSTE) of USP.

2.2.2 Storage of tissue samples

Toe samples were stored in individual 1.5 ml Eppendorf tubes containing

~0.5 ml of absolute ethanol for up to two weeks during fieldwork at room

temperature; thence after at -80 °C in the laboratory. Samples were stored at this

ultra-low temperature for up to four months prior to DNA extraction.

2.2.3 DNA extraction protocol

DNA from individual toes was extracted using a QIAgen DNeasy™ kit

protocol (QIAgen). Toes were cut up using a sterile scalpel blade and Petri dish.

The blade and dish were rinsed with 95% ethanol between individual samples. A

new blade and dish were used for each frog population. The toe pieces were placed

in sterile appropriately marked 1.5 ml Eppendorf tubes, and 180 μl of Buffer ATL

(tissue lysis buffer) and 20 μl of Proteinase K. Tissue samples were left to undergo

tissue lysis on a heat block at 56 °C for up to 5 hours or overnight at 40 °C.

27

Once tissue lysis was deemed complete (no visible remnants of bone or skin

tissue), samples were vortexed for 15 seconds. 200 μl of Buffer AL (cell lysis) and

200 μl of absolute (97-100%) ethanol were added and each sample was vortexed

immediately for ~10 seconds. The resulting solution was pipetted into clean filter

columns and collection tubes and centrifuged at 8000 rpm for 60 seconds. Collection

tubes were discarded and filter columns were placed in clean collection tubes. 500

μl of Buffer AW1 (wash buffer containing absolute ethanol) was pipetted into each

filter column and samples were centrifuged at 8000 rpm for 60 seconds.

Flow-through and collection tubes were discarded again and filter columns

placed in clean collection tubes. 500 μl of Buffer AW2 (wash buffer containing

absolute ethanol) was pipetted into each filter column and samples were centrifuged

at 13400 rpm for five minutes. Flow-through was discarded and filter columns and

collection tubes were re-used in a second centrifuge step at 13400 rpm for 60

seconds to dry the filter membrane. Flow-through and collection tubes were then

discarded and the filter columns placed in clean 1.5 ml Eppendorf tubes. 200 μl of

Buffer AE (elution buffer) was pipetted directly onto each filter membrane and the

tubes were centrifuged at 8000 rpm for 60 seconds.

This final elution step was repeated using the filter columns in second spin

with another clean Eppendorf tube and an additional 200 μl of Buffer AE. The

eluates were combined to produce 400 μl of eluted DNA per sample. The second

elution step was recommended to maximise the DNA yield per sample. DNA yield

was confirmed on a 1% agarose gel and quantified using a Nanodrop ND-1000

spectrophotometer (NanoDrop Technologies, Inc).

2.2.4 Other methods used

For several samples, DNA was extracted using a standard

hexadecyltrimethylammonium bromide (CTAB) or phenol chloroform protocol

(Doyle and Doyle 1990). A 2X CTAB buffer was prepared by combining 100 mM

Tris-HCl (pH 8.0), 20 mM EDTA, 1.4 mM NaCl, 2% CTAB, and 0.2% 2-

mercaptoethanol. Toe samples were cut up and placed in clean 1.5 ml Eppendorf

tubes, as described in the previous section. 300 μl of the prepared CTAB buffer

(pre-heated to 60 ºC on a heat block) and 10 μl of Proteinase K were added to the

samples. The samples were vortexed and incubated on the heat block for ~ 2 hours

(or until the tissue lysis was deemed complete).

28

300 μl of phenol and 300 μl of chloroform (24:1) were added to the lysed

tissue solution under a fume hood. The solutions were then pipetted for several

minutes to mix completely the phenol and chloroform. Samples were then

centrifuged at 14000 rpm for 10 minutes. The clear supernatant containing the

extracted DNA was then pipetted into a clean 1.5 ml Eppendorf tube. Addition of

phenol and chloroform, centrifuging and removal of the supernatant were repeated

when the solutions remained coloured (yellowish) after the centrifuge step. Two

volumes (relative to the volume of clear supernatant from the previous step) of ice-

cold 80% ethanol were added to the DNA solutions.

The tubes were inverted several times to mix the ethanol and aqueous DNA

and then centrifuged at 14000 rpm for 10 minutes. The ethanol was then pipetted out

and the tubes air-dried on a heat block (at 56-60 ºC). The dry DNA pellet (visible as

a small white mass at the bottom of the tube) was then re-suspended in 30 μl of 0.1X

TE and the DNA solution kept at four ºC before being checked on an agarose gel.

2.2.5 Storage of extracted DNA samples

From the 400 μl DNA stock solutions, two 50 μl aliquots were taken and

stored at -20°C for PCR protocols. DNA stock solutions were then stored at -80°C in

a Forma -8680°C ULT Freezer (Thermo Electron Corporation) for later use.

29

CHAPTER THREE

SPATIAL ANALYSES OF ABUNDANCE AND DISTRIBUTION

30

3.1 INTRODUCTION

The rate of loss of amphibian biodiversity is identified as one of the most

recognizably alarming crises faced by any taxa (Stuart et al. 2004; Fouquet et al.

2010). Documented population declines and extinctions together with the well-

recognised sensitivity of amphibians to environmental change have resulted in

amphibians, and in particular frogs, being recognised as key indicators of the status

or health of the environment (Wake 2012; Wake and Vredenburg 2008). This

indicator status is very useful for tropical countries including Fiji where the rate of

environmental degradation requires urgent attention, and funding limitations are

often imposed on the breadth and depth of amphibian research. Knowledge regarding

the status of biodiversity provides evidence for informed decision-making and

appropriate management interventions.

Fiji represents the easternmost extent of the family Ceratobatrachidae and the

genus Cornufer (sub-genus Cornufer), and the genus includes extinct, threatened and

endangered species that are biogeographically and evolutionarily enigmatic with

much morphological diversity. The Fijian archipelago was prehistorically home to

three Ceratobatrachid species, which existed in sympatry: C. megabotovitiensis, C.

vitianus, and C. vitiensis (Worthy 2001). Shifting ranges of their forest habitat in

combination with predation pressure (by humans and introduced species) are the

most likely agents of extinction for C. megabotonivitiensis and decline of

populations of C. vitianus. C. vitianus is considered ‘endangered’ (EN B1ab[v]) and

C. vitiensis ‘near threatened’ (NT) under the IUCN classification system (IUCN

2014). A call has been made to have C. vitiensis’ status changed to ‘vulnerable’ (V

B1ab[v]), based on an apparent decline in range (Osborne, T. et al. 2013).

The distribution of the two species in Fiji has been established by Gorham

(1968, 1971), Ryan (2000), Morrison et al. (2004) and Zug (2013). The range of C.

vitiensis is thought to have extended throughout the western and central parts of Fiji

before human arrival (Gorham 1968; Pernetta and Goldman 1977), but this is now

reduced to the two largest islands of Viti Levu and Vanua Levu. Cornufer vitianus is

recorded on Viti Levu (in Nakauvadra where there is a small isolated population),

Vanua Levu, Taveuni, Gau, Ovalau, and Viwa. Populations on Koro, Beqa and

Kadavu Island have been reported (Morrison 2003), although these have not been

verified in recent field studies.

31

Habitat and climatic variables are the most commonly cited factors to

consider when predicting anuran distributions (Mantyka-Pringle et al. 2012). For the

Cornufer spp. in Fiji, a strong affinity to primary rainforest (particularly with intact

riparian systems) has been demonstrated previously (Osborne et al. 2008; Thomas et

al. 2011). However, C. vitianus can also be found in marginal habitats such as

cultivated Colocasia esculenta fields and forest edges. Range reduction of either

species, previously thought to be an outcome of forest clearing/loss, may be

complicated for Fijian Cornufer. As these species can persist in marginal habitats a

simple correlation between decreasing primary forest habitat availability would be

difficult to determine. It is likely that a complex relationship exists between climatic

change and biotic response within forest ecosystems, which would require in-depth

investigation.

Investigation of species geographic distributions using the ever-improving

data analysis functions of GIS software have become commonplace in biodiversity

research (Metzger et al. 2013). Descriptions of species incorporate a determination

of the spatial characteristics of distribution (Kareiva and Marvier 2003; Fischer et al.

2010; Mindell et al. 2011). For example, hotspot and/or cold spot analysis as applied

in ArcGIS™ software is commonly utilised to identify relationships between

environmental variables and species presence and/or abundance information (Costa

et al. 2010; Krasnov et al. 2010).

Species distribution modelling (SDM) has been used widely for the mapping

of the suitability of organisms to geographical areas of interest. It is now a

commonly applied approach in biodiversity conservation with uses that include the

identification of areas for future surveys (Araujo and Guisan 2006). Maps created

with SDM help in prioritising study areas - an important consideration in view of

limited resources, particularly with respect to expertise and funding required for field

studies. Previous analyses have helped in the discovery of new species that may have

remained unknown without the initial guidance of SDMs (Raxworthy et al. 2003)

used to prioritise sampling areas. SDM software has been developed that employs a

wide variety of approaches and algorithms. Such methods usually generate

probability distribution maps of study areas showing levels of suitability of each

pixel or cell of the image for a particular organism (Higgins et al. 2012; Sanchez-

Cordero et al. 2004).

32

Species Distribution Modelling (SDM) has also been employed in predicting

species invasion or proliferation (Roura-Pascual et al. 2008; Poulus et al. 2012;

Youhua 2008; Thuiller et al. 2005), and potential habitat suitability for threatened

and/or endangered species (Bombi et al. 2009; Puschendorf et al. 2009; Wang et al.

2012; Wilson et al. 2011). The utility of SDM includes descriptions of temporal and

spatially-based scenarios, and the projection of species distribution into unexplored

or little-studied areas, as well as into future and past conditions (Nabout et al. 2010;

Yates et al. 2010). I herein report distribution models for C. vitianus and C. vitiensis

that were developed using recently published field survey data. I investigated the

utility of using global climate data to predict local distribution, and also assess the

suitability of islands within the Fiji group for these species. These analyses may be

used to provide a framework for future surveys and modelling of the distribution of

Fijian endemic species.

3.2 METHODS

3.2.1 Location and count data for frog populations

Thirty-two independent sites (each site separated by >10 km) from six islands

in the Fijian archipelago were surveyed in order to gather presence data and

environmental condition parameters (Figure 3.1). Sampling sites were selected

based on: primary or secondary re-growth forest; moderate to high tree density;

proximity to water bodies (i.e. streams or ponds); anecdotal reports of frog

populations being present; and proximity to other areas sampled. Primary rainforest

sites were preferred to secondary vegetation as populations were presumed to be

greater in less disturbed habitat. Surveys were conducted in more disturbed

vegetation if there were anecdotal reports of frog populations in the vicinity.

Surveys were conducted on the islands of Viwa, Ovalau, Taveuni, Vanua

Levu, Viti Levu and Gau. Each site was surveyed for two to three hours at night by a

sampling team of four to five researchers. Searches were made in vegetation, leaf

litter and along stream banks for either species. Where both species were found in

sympatric populations, some searchers focussed efforts on the arboreal C. vitiensis,

whilst others searched for the ground-dwelling C. vitianus. To standardise survey

efforts the number of searchers and the length of time surveying was kept constant.

33

Fi

gure

3.1

Fro

g po

pula

tions

on

the

six

isla

nds s

urve

yed,

gra

phed

aga

inst

ann

ual p

reci

pita

tion

(mm

) fro

m B

ioC

lim.

34

Table 3.1 Habitat Codes for Quantitative Analyses in ArcMap.

ID Habitat Type

1 Coastal beach forest

2 Coastal beach forest and plantations

3 Plantations

4 Plantations and human habitation

5 Secondary lowland rainforest and plantations

6 Secondary lowland rainforest

7 Primary lowland rainforest

8 Secondary mid-highland rainforest

9 Primary mid-highland rainforest

10 Secondary highland rainforest

11 Primary highland rainforest

ID Canopy Cover

1 <20%

2 20-40%

3 40-60%

4 60-80%

5 80%

6 >90%

ID Disturbance Level

1 <20% Low

2 20-40% Low to moderate

3 40-60% Moderate

4 60-80% Moderate to high

5 >80% High

35

Global Positioning System (GPS) locations in Fiji Map Grid coordinates

(1986) and frog abundances (captures only) were recorded for each site where frogs

were surveyed. Habitat information such as percent canopy cover, stream width,

human modification and natural disturbance (mainly due to cyclones), and vegetation

type were also recorded (refer to Table 3.1 for categories used).

3.2.2 GIS layers and analyses

BioClim data (19 climatic global data layers) from the global website

(www.bioclim.org) were downloaded (Hijman et al. 2004). The raster layers were

clipped to the Fijian archipelago area (excluding the outlier island of Rotuma).

Absolute count data at each site were analysed using the statistical analysis tools of

ArcMap 10, investigating five environmental variables (percent canopy cover, stream

width (m), percent disturbance, and habitat type; refer to Table 3.2). In addition, frog

abundance was correlated with the BioClim data using exploratory regression and

Ordinary Least Squares (OLS) analyses in ArcMap 10 to identify important climatic

influences on distribution of the Fiji frogs.

3.2.2.1 OpenModeller analyses

For species distribution modelling, BioClim raster layers were clipped to the

Fiji Islands area, converted to ASCII format in ArcMap, and used in OpenModeller.

All the algorithms in OpenModeller were trialled and those that ran to completion

were selected including BioClim (Nix 1986), Climate Space Model, Envelope Score

(Nix 1986; Pineiro et al. 2007) Environmental Distance (Carpenter et al. 1993);

GARP Single Run – DesktopGARP and new OpenModeller Implementations

(Stockwell 1999; Stockwell and Peters 1999), Niche Mosaic, and Support Vector

Machines (Cristianini and Shawe-Taylor 2000; Schölkopf et al. 2000 and 2001).

These algorithms were used to generate SDMs showing the predicted distribution for

Fijian Ceratobatrachids.

36

Table 3.2 BioClim data for sampled populations of Fijian Cornufer used in spatial

correlation analyses.

Layer Climatic Variable Units Significance€ OLS

BIO1 Annual Mean Temperature °C 19.17 NS*

BIO2 Mean Diurnal Range (Mean of monthly (max temp - min temp)) °C 12.25 p(df= 4,52)=0.0456

BIO3 Isothermality (BIO2/BIO7) (* 100) °C 12.92 NS BIO4 Temperature Seasonality (standard deviation *100) °C 8.72 p(df= 4, 52)=0.0066

BIO5 Max Temperature of Warmest Month °C 38.83 NS BIO6 Min Temperature of Coldest Month °C 21.84 NS BIO7 Temperature Annual Range (BIO5-BIO6) °C 14.33 NS BIO8 Mean Temperature of Wettest Quarter °C 19.29 NS BIO9 Mean Temperature of Driest Quarter °C 28.21 NS BIO10 Mean Temperature of Warmest Quarter °C 17.79 NS BIO11 Mean Temperature of Coldest Quarter °C 28.24 NS BIO12 Annual Precipitation mm 17.66 p(df= 4, 52)=0.0219

BIO13 Precipitation of Wettest Month mm 93.87 p(df= 4, 52)=0.0038

BIO14 Precipitation of Driest Month mm 6.18 NS BIO15 Precipitation Seasonality (Coefficient of Variation) mm 10.33 NS BIO16 Precipitation of Wettest Quarter mm 20.08 NS BIO17 Precipitation of Driest Quarter mm 9.24 NS BIO18 Precipitation of Warmest Quarter mm 27.27 NS BIO19 Precipitation of Coldest Quarter mm 9.78 NS FS01 Site habitat/vegetation type --- 6.25 NS FS02 Canopy cover % 43.75 NS FS03 Disturbance level (natural and human) % 31.25 NS FS04 Stream width (stream presence) m 100 p(df= 4, 52)=0.0007

FS05 Elevation (metres above sea level) m 100 p(df= 4, 52)=0.0003

NS* - Not statistically significant (p>0.05) € - Percent significance of variable to all regression models in exploratory analysis

37

Model parameters were kept at the default values for all the 13 algorithms

available in OpenModeller V1.1.0. Each algorithm was run with both species’ data

and the resulting distribution images loaded onto ArcMap 10. Consensus SDM maps

for each species were ‘ensembled’ in ArcMap by adding the pixel values (from each

of the SDMs generated using OpenModeller) using the cell raster tool. Ensemble

modelling is becoming an increasingly accepted approach to species distribution

modelling as a means to overcome the discrepancies of the results of individual

models or algorithms (Araujo and Guisan 2006; Stohlgren et al. 2010).

Areas with greater than 60% probability (suitability) of frogs occurring were

calculated using the zonal histogram tool. A less conservative estimate was made at

greater than 40% probability. I used the zonal histogram tool in ArcMap 10 to

generate a table of pixel counts for each category of the consensus SDM map legend.

The percentage of total pixels in each suitability category was used to calculate the

approximate land area for each species’ consensus SDM.

3.2.2.2 ArcGIS analyses

An Ordinary Least Squares (OLS) test was performed on the BioClim data to

determine the effects of the environmental parameters on frog abundance. The

results of the OLS were used as the basis for a Geographically Weighted Regression

(GWR) using the input variables identified in the OLS as probable influences on

distribution and abundance. The outputs of a GWR can be particularly useful in

describing relationships that may be insufficiently described by OLS (Aguilar and

Farnworth 2012; Shi et al. 2006; Table 3.2).

Hotspot analysis was executed using the Getis-Ord (Gi*) algorithm included

in ArcMap. These ‘hotspots’ or ‘coldspots’ refer to study sites with relatively higher

or lower concentrations of frogs, respectively (Getis and Ord 1992; Ord and Getis

1995; Ord and Getis 2001). The Gi* statistic is a z-score; for statistically significant

(α=0.05) positive z-scores, a larger z-score in this analysis represents clustering of

areas with high abundance of frogs (hotspots) while for statistically significant

negative z-scores the smaller z-score is associated with a clustering of areas where

frogs are absent or of low abundance (coldspots). Related applications of spatial

clustering using the Gi* statistic in ecology and species distributions include the

work of Dennis et al.(2002), Shaker et al. (2010), and Rissler and Smith (2010). The

38

Getis-Ord analysis was conducted with parameters set to the ‘inverse distance

squared’ with a threshold distance of 20 m.

The Getis Ord Gi* statistic is useful for identifying hotspots and coldspots,

but specific areas that exhibit statistically significant spatial outliers can be identified

by the Anselin’s Local Moran’s I approach (Anselin 1995). Anselin’s Local Moran’s

I estimates the similarity or dissimilarity of a feature with surrounding features.

Inverse weighted distance squared and the Euclidean distance measurement was

employed as options in the analysis. Groupings of positive Anselin’s Local Moran’s I

values with significant z-scores showed evidence of clustering while groupings of

negative spatial autocorrelation indices provides indication of a lack of clustering.

Results of Anselin’s Local Moran’s I with statistically significant indices

(α=0.05) are classified using local and global means of frog counts (local means

refer to the average frog counts per site): HH indicates areas with local means higher

than the global mean; LL indicates areas with local means lower than the global

mean; HL indicates areas with values higher than the local mean and LH indicates

areas with values lower than the local mean (Mitchell 2005). Moran’s spatial

autocorrelation or ‘cluster analysis’ was performed using a width of 10 m between

points. The Anselin’s ‘cluster and outlier’ test was run using default parameters.

Similarly, environmental variables (habitat type, canopy cover, disturbance,

and stream presence/width) recorded at the sampling sites and elevation data were

used as independent variables to model frog abundance using OLS, GWR, hotspot

analysis, and Anselin’s Local Moran’s I test. Elevation or altitude for each of the

frog sampling sites were generated from downloaded Shuttle Radar Topography

Mission (SRTM) images (Rabus et al. 2003) using the raster sampler tool in ArcGIS.

The resolution for SRTM files is 30 m (1 arc-second); the low resolution results in

several low-lying coastal sites appearing to be off shore. As a result several sites

were excluded from the ArcMap output (three from Viwa and two from Ovalau), and

the statistical analyses.

3.3 RESULTS

3.3.1 Spatial analyses of frog distribution and abundance data

The ground frog C. vitianus populations were distributed widely throughout

all of the five smaller islands, a combined landmass of 6261.1 km2, of which

approximately 45% is forested (Figure 3.1). The only known remnant population on

39

the mainland, in the Nakauvadra Range, is probably spread out over ~115 square

kilometres of the highland area. The ground frog was found in a diverse range of

habitats, from primary lowland to highland rainforest, secondary re-growth forests,

plantations, and coastal littoral forest with relatively moderate disturbance levels.

Populations were recorded at eight previously unreported locations (three on Ovalau,

two on Taveuni, and three on Vanua Levu).

The tree frog C. vitiensis was found on two (Vanua Levu and Viti Levu) of

the four islands where this species is thought to occur. A relatively large population

of C. vitiensis was found in the Waisali Reserve, on Vanua Levu Island. C. vitianus

are found sympatrically in this area. C. vitiensis populations persist in less disturbed

lowland to highland rainforest, as well as in cultivated forestry reserves on the main

island of Viti Levu (Osborne et al. 2008). Tree frog populations were recorded at 10

of the 32 survey sites ranging from western Viti Levu to the south east of the island.

Of the 19 climatic variables available on the BioClim global database, four

variables (mean diurnal temperature range BI02, temperature seasonality BI04,

annual precipitation BI013, and precipitation of wettest month BI014) were

identified as influential factors shaping distribution and affecting local population

abundance of Fijian Ceratobatrachids (Table 3.2). Significant OLS p-values were not

affected by spatial autocorrelation (Moran's Index: -0.025957, p = 0.383170; Figure

3.2a).

The GWR test failed due to the multicollinearity of the BioClim data (many

variables were correlated or derived from each other) as shown in an earlier

exploratory regression (no models were passed as significant). Of the models tested

in the exploratory regression, more than 95% indicated that precipitation of the

warmest month (variable BI013) was a significant climatic factor.

There were Anselin clusters on Ovalau and Taveuni for C. vitianus, and

Vanua Levu and Viti Levu for C. vitiensis (Figure 3.2c). Several frog populations

were classed as Getis-Ord ‘hotspots’: Koromakawa (Nasaga, Ovalau), Vunisea

(Nakauvadra, Viti Levu), Nadi-i-cake (Nadivakarua, Vanua Levu), and Lomalagi

(Somosomo, Taveuni).

For the four habitat variables collected during surveys, only stream width

(which indirectly indicated stream presence at the sample site) was significant

(r2=0.396, p =0.0004, d.f. = 32) in the OLS analysis (Figure 3.2). Elevation exerted a

very significant negative influence on overall frog abundance (p<0.01) in all the

40

models tested in the exploratory regression performed in ArcMap. Frog abundance

in the Waisali Reserve (Vanua Levu) was significantly higher than all the other

sample sites (>2.5 SD). Populations of C. vitianus on Ovalau and Viwa Island had

higher than average abundance. The GWR result mirrored the OLS in that it

identified the ‘higher than average’ C. vitianus abundance on Ovalau and Viwa

(+1.5-2.5 SD). Overall the regression model had an r2 value of 0.27.

Clustering analyses (Moran’s and Anselin’s tests) suggested that there was no

observable clustering pattern in the distribution of either frog species (Moran’s test,

p=0.38). Two ‘high abundance’ populations adjacent to ‘low abundance’

populations were identified in the Anselin cluster and outlier analysis – Waisali

Reserve and Loru, Ovalau (Figure 3.2a). The result of the Getis-Ord ‘hotspot’

analysis highlighted the healthy state of C. vitianus populations on Gau which have

been recorded in previous surveys (Kuruyawa et al. 2004).

3.3.2 Spatial analyses of Species Distribution Models (SDMs)

Seven of the 13 algorithms in OpenModeller produced species probability

distribution maps (SDMs) for both frogs (Table 3.3). The consensus SDMS for each

species had several interesting features (Figure 3.3). Firstly, both maps predicted the

persistence of a population of either Cornufer species occurring on Koro Island.

There were no frog counts from the island in the current study, but five of the seven

SDMs (for both species) indicated high suitability for Koro Island.

Both consensus maps indicated the low suitability of high altitude forests

(>600 km a.s.l) as habitat for Fijian frogs. It is important to note here the terrain and

the resulting vegetation structure of these high altitude sites in the Fiji Islands; these

sites are typically mountain peaks or ridge tops and as a result vegetation is

consequently stunted montane rainforest and/or ‘cloud forest’ (Watling and

Gillison1993). Canopy cover in these high altitude sites is patchy (<20%) and tree

cover increases in density downslope (Merlin and Juvik 1993).

The analysis of residual autocorrelation indicated that with increasing

elevation, there were narrower streams, less disturbance, and thicker vegetation cover

(canopy density). The OpenModeller SDMs and results of the OLS in ArcMap

indicated that lowland to mid-highland areas were more suitable for C. vitiensis,

whilst C. vitianus was likely to occur anywhere from the coast to sub-montane

forests.

41

In terms of overall area calculated from the histogram of pixels with values

above the threshold of 60%, the consensus SDM maps predicted probable

distributions of 8,566 km2 for C. vitianus and 5,933 km2 for C. vitiensis (total land

area of the Fijian archipelago is 18, 274 km2). An IUCN Red Listing criterion for the

Vulnerable (VU) category demarcates a geographic range of 20,000 km2 for the total

expected ‘extent of occurrence’ of a threatened species. C. vitiensis’s predicted

distribution therefore was substantially below the vulnerable threshold, and actually

came very close to the ‘Endangered’ category extent of occurrence (< 5,000 km2).

The less conservative 40% threshold, suggests a predicted distribution of 11,272 km2

for C. vitianus and 8,806 km2 for C. vitiensis.

3.4 DISCUSSION

3.4.1 Broad-scale habitat preferences indicated by ArcGIS

Rainfall distribution across the Fiji Islands probably indirectly (through its

influence on vegetation/habitats) and directly (atmospheric moisture, leaf litter

moisture, and humidity levels) affects where Fijian Cornufer populations persist as

well as their local abundance. It was therefore not surprising that annual rainfall at a

site (BioClim variable BI012), and rainfall of the wettest month (BI013) were the

two most significant influences as both are often used as measures indicating

location within the Fiji climatic zones (broadly known as wet and dry zones). Mean

diurnal range and temperature seasonality were also good climatic indicators of

location in Fiji, and these were the only two temperature variables (of the 11) that

were significant. The role of diurnal temperature range for nocturnal ectothermic

amphibians has been well studied and many studies indicate activity levels drop with

decreasing temperature (Zheng and Liu 2010).

Rainfall also plays a well-defined role in the evolution of fluvial landscapes.

Stream presence in the forests where frogs persist appeared to greatly increase the

abundance of populations. Ceratobatrachids are direct developing anurans and the

affinity of Fijian frogs for streamside habitats begs further investigation as

preliminary field studies have identified this interaction with their environment

(Osborne et al. 2008). The significantly higher-than-average frog abundance at the

Waisali Reserve may be linked to the large river network in this part of the Wailevu

(literally translated as ‘river’) district.

42

Figu

re 3

.2 S

patia

l ana

lysi

s map

s sho

win

g th

e

influ

ence

of e

nviro

nmen

tal v

aria

bles

reco

rded

at t

he sa

mpl

e si

tes:

(a) G

etis

-

Ord

‘hot

spot

’ ana

lysi

s whi

ch p

rodu

ces

Get

is-O

rd R

esid

uals

(ref

er to

key

),

used

to c

ompa

re ‘h

otsp

ots’

in re

d to

‘col

dspo

ts’ i

n da

rk b

lue;

(b) O

rdin

ary

Leas

t Squ

ares

(OLS

) whi

ch p

rodu

ces

gene

ral r

egre

ssio

n re

sidu

als t

hat

iden

tify

site

s with

sign

ifica

ntly

hig

h

frog

abu

ndan

ces (

red

circ

les)

or l

ow

abun

danc

es (d

ark

blue

) in

rela

tion

to

the

envi

ronm

enta

l par

amet

ers a

t the

site

; (c)

Ans

elin

’s c

lust

er a

naly

sis

whe

re n

eigh

bour

ing

site

s tha

t hav

e

sign

ifica

ntly

diff

eren

t abu

ndan

ces o

f

frog

s (se

e th

e A

nsel

in C

lust

er k

ey) a

re

show

n by

gre

en c

ircle

s; a

nd (d

)

Geo

grap

hica

lly W

eigh

ted

Reg

ress

ion

(GW

R) w

here

site

s with

sign

ifica

ntly

high

frog

abu

ndan

ces a

re sh

own

as

red

circ

les a

nd th

ose

with

sign

ifica

ntly

low

abu

ndan

ces a

s dar

k bl

ue c

ircle

s.

(a)

(b)

(c)

(d)

43

Table 3.3 OpenModeller (Version1.1.0) SDM algorithms tested against Fijian

Cornufer spp. SDM Evaluation

Algorithm FGF FTF

Artificial Neural Network (ANN) X# X

BioClim Satisfactory Satisfactory

Climate Space Model (CSM) Poor Satisfactory

Envelope Score (EScore) Poor Satisfactory

Environmental Distance (EDist) Good Poor

Maximum Entropy (Maxent) X X

Environmental Niche Factor Analysis (ENFA) X X

GARP Single Run (OpenModeller Implementation) (GSRoM) Good X

GARP Best Subset (OpenModeller Implementation) (GBSoM) X X

GARP Single Run (Desktop GARP) (GSRDG) Satisfactory X

GARP Best Subset (Desktop GARP) (GBSDG) X X

Niche Mosaic (NMos) Satisfactory Satisfactory

Support Vector Model (SVM) Poor Poor

X# - Run failed and no output SDM

44

Fi

gure

3.3

a C

onse

nsus

map

gen

erat

ed b

y A

rcM

ap u

sing

spec

ies d

istri

butio

n m

odel

s gen

erat

ed b

y O

penM

odel

ler f

or C

ornu

fer v

itian

us.

Ref

er to

Tabl

e 2

for d

escr

iptio

n of

the

mod

el la

yers

incl

uded

in a

naly

sis.

45

Fi

gure

3.3

b C

onse

nsus

map

gen

erat

ed b

y A

rcM

ap u

sing

spec

ies d

istri

butio

n m

odel

s gen

erat

ed b

y O

penM

odel

ler f

or C

ornu

fer v

itien

sis.

Ref

er to

Tab

le 2

for d

escr

iptio

n of

the

mod

el la

yers

incl

uded

in a

naly

sis.

46

Populations on Ovalau and Viwa also were significantly higher in abundance.

Viwa is a small 0.6 ha island where attempts have been previously made to eradicate

rats and cane toads from the island (PII 2009). The conservation effort, in addition to

increasing awareness of frog conservation for the local residents of the island, has

hopefully served to increase the likelihood of persistence for this endemic frog

population. On Ovalau, one population (Loru) was greater in frog abundance than

all the others combined. It was likely that the OLS and GWR result was skewed by

the frog count at this pristine sub-montane forest site. Populations elsewhere on the

island were much smaller in comparison and persisting in disturbed human modified

landscapes.

Although there was no significant clustering pattern, the analyses do highlight

the value of both the Waisali Reserve and Loru frog populations as probable source

areas from which neighbouring smaller frog populations may receive migrants to

boost population sizes. Another location of note was the ‘hotspot’ island of Gau

where C. vitianus populations were not subject to the twin pressures of competition

(with the invasive cane toad) and predation by the small Indian mongoose (Herpestes

javanicus).

3.4.2 Species distribution modelling for the Fiji Frogs

In the same vein, the proximity of Koro Island to Taveuni and Vanua Levu

would increase its likelihood as a ‘hotspot’ for either frog species, and our SDMs

concurred. Anecdotal records (Morrison 2003) suggest that there may be a persistent

population of C. vitiensis on Koro Island despite human modification to much of the

landscape on the island. The degree to which the OpenModeller SDMs emphasized

Koro as a ‘suitable’ site for frog populations requires further investigation. The

entire volcanic island was classified as greater than 50% ‘suitable’ for both C.

vitiensis and C. vitianus. Koro is the sixth largest island (108.9 km2) in the Fijian

archipelago and is estimated to have approximately 80% intact or ‘closed forest’

cover in the central parts of the island (based on Google Earth images).

Cornufer vitianus has a higher chance of persisting in mesic coastal habitats

than C. vitiensis, which is more common in primary forested inland areas. Our

findings support previous work (Osborne et al. 2008), namely that C. vitiensis has a

greater affinity for low disturbance sites and additionally, that C. vitiensis is more

vulnerable to forest loss than C. vitianus (Osborne et al. 2008; Thomas et al., 2011).

47

The marked difference in average body size between the two species would influence

their comparable rates of desiccation, and therefore responses to change in canopy

cover. Body size would also play a key role in determining the suitability of high

altitude habitats for either species.

High altitude areas were predicted as unsuitable habitat for Fijian frogs, and

particularly for C. vitiensis, the smaller of the two species. In general, Cornufer are

more likely to be found on the forested slopes or river valleys of Fiji’s highlands,

rather than on ridge tops or peaks where stunted vegetation and more extreme

microclimates (from greater exposure to wind and sunlight) creates less suitable

microhabitats. Low nocturnal temperatures at high altitudes would be less

favourable for the smaller of the two Cornufer species (Navas 1996). The influence

of altitude on Fijian frogs begs further investigation in the light of global climate

predictions (Wake 2012).

Overall, the SDM consensus maps predicted a greater area of occupancy for

C. vitianus compared to C. vitiensis. This would provide further weight to the

growing field evidence that C. vitiensis’ range may be less than the IUCN Red List

‘vulnerable’ category range of 20,000 km2 and may be closer to ‘endangered’ (EN

B1ab[v]). The utility of SDMs for classifying Fijian endemics such as the

Ceratobatrachid frogs against stringent Red List criteria is very promising; this might

provide a method of augmenting classification when confronted with limited field

survey data. Rapid Biodiversity Surveys (RAPs), such as those conducted for the

purpose of Environmental Impact Assessments (EIAs) can be useful for generating

location and count data that can then be fed into SDMs. Particularly, considering that

Fiji’s conservation community (government and NGO) is limited in its capacity (by

funding and scientific expertise) for extensive surveys and long-term population

monitoring.

56

CHAPTER FOUR

MITOCHONDRIAL GENE ORDER AND EVOLUTION

57

4.1 INTRODUCTION

Understanding of genomic order and content in vertebrates is progressing

with advances in high throughput or next-generation sequencing (NGS). Some of the

insights that have been developed from genomic studies of anurans include a rapid

assessment of a species’ population genetic diversity and structure (Zavodna et al.

2013), estimation of clade divergences in deeply rooted phylogenies as far back as

300mya (Zhang et al. 2013), and investigating the root of the somewhat contentious

frog Tree of Life (Irisarri et al. 2012). Due to the size of the genome and the

efficiency with which mtDNA data can be used to reconstruct phylogenies of varying

taxonomic depth, mitochondrial genes are still one of the primary types of loci

surveyed in anuran phylogenetic studies (Zhang and Wake 2009; Pyron and Wiens

2011; Zhang et al. 2013).

At present there is no consensus regarding what constitutes a standard

arrangement for mitochondrial genomes of anurans, due to the variability in gene

order in addition to the presence of duplicated segments. Non-coding regions of the

mitogenome such as the control region present obstacles for sequencing due to rapid

evolution rates and the guanine-cytosine bonding in these G-C rich loci (Meyer et al.

2010). Many of these ‘near complete’ genomes have been used unreservedly in

recent phylogenetic reconstructions of the Anura (e.g. Zhang et al. 2013). More

recent phylogenetic reconstructions using ‘next-generation sequencing’ (NGS)

technology have forgone the control region, “barcoding” gene fragments (CO1) or

the widely used 16S ribosomal sub-unit, as a data resource eliminating the

problematic control region from analyses of mitogenomic evolution within the Anura

(Kurabayashi and Sumida 2013; Zhang et al. 2013). In the previous decade, partial

control region sequences were used to determine phylogenies due to the length of the

marker and the high substitution rate (San Mauro et al. 2005; Gissi et al. 2006b).

All of the fully-sequenced anuran mitochondrial genomes currently

accessioned on the NCBI database GenBank have a continental distribution

(including species found on continental fragments). The paucity in genomic data

from insular species, particularly anurans from biodiverse tropical islands, can be

attributed to the lack of scientific infrastructure in these developing economies. The

wholly tropical genus Cornufer (sub-genus Cornufer) is a good example of an

amphibian taxon that has yet to be added to GenBank’s whole genome accessions.

58

The genus includes extinct, threatened and endangered species that are

biogeographically and evolutionarily enigmatic with an amazing array in intra-

specific phenotypic diversity. The Fijian archipelago, representing the easternmost

extent of the family Ceratobatrachidae (represented by the genus Cornufer, sub-

genus Cornufer), was prehistorically home to three Ceratobatrachid species, which

existed in sympatric populations: C. megabotovitiensis, C. vitianus, and C. vitiensis

(Worthy 2001).

I herein describe gene organization and gene duplications in the

mitochondrial genomes of C. vitianus (from Viti Levu and Taveuni) and C. vitiensis.

The ground frog genome from Viti Levu was characterized by Sanger sequencing

using the ABI3730 platform of long-PCR products and primer walking, while that of

a ground frog from Taveuni and a Tree frog from Viti Levu were characterised by

sequencing genomic DNA extracts on the Illumina sequencing platform. Genes

extracted from the assembly of these genomes were then used in phylogenetic

reconstructions with 43 amphibian genomes sampled from GenBank. Models of

substitution, specific to protein coding regions and to ribonucleic acid regions (RNA)

in this dataset (individual and concatenated genes) were determined using

jModelTest2 (Darriba et al. 2012). Phylogenetic reconstructions were made for

individual genes and concatenated data.

Of particular interest, was obtaining preliminary estimates for the divergence

times of Fijian frogs, and also in obtaining lineage specific estimates of substitution

rate for different genes. This was of interest, because some Neobatrachian frogs

show significant reorganization of their mitochondrial genomes and published

phylogenies suggest elevated rates of substitution in their mitochondrial genomes.

The cluster of five genes coding to transfer RNAs (tRNAs) plus the site of initiation

of replication of the lagging or light strand (OL), known as the “WANCY” region

(Seutin et al. 1994) is a well publicized hotspot for gene duplication and gene

translocation in anurans (Macey et al. 1997; San Mauro et al. 2005; Kurabayashi et

al. 2008). In plastid genomes regions of accelerated substitution, indels and genome

rearrangement are thought to be correlated (Ahmed et al. 2012; Weng et al. 2013).

59

4.2 METHODS

4.2.1 Sequencing of mitochondrial genomes of Fiji frogs

DNA from individual toes collected (refer to chapter 2 for detailed field and

DNA preparation methods) was extracted using a QIAgen DNeasy™ kit protocol

(QIAgen). Individual DNAs of C. vitianus and C. vitiensis provided sufficient DNA

(1-2 ug) for both long range PCR and sequencing on the Illumina GAIIx™ platform.

4.2.2 Long range PCR and Sanger sequencing using ABI3730 platform

Mitochondrial genome sequences from C. vitianus (Viti Levu) were

amplified in two ten kilobase (kb) fragments using a long-PCR touchdown

polymerase chain reaction (PCR) protocol (Don et al. 1991; Briscoe et al. 2013) and

DreamTaq polymerase following the manufacturer’s protocol (Thermo Fisher

Scientific, Waltham, MA). A third overlapping sequence was then generated from

long-PCR to ensure sufficient coverage of the unknown gap.

These three large products were run on 1% (w/v) agarose gels in 1 x TAE

buffer and the fragments were extracted using a Zymoclean Gel DNA Recovery Kit

(Zymo Research Corp, Irvine, CA). The long-PCR amplicons were used as DNA

templates to subsequently sequence smaller (~1-8kb) overlapping fragments using a

traditional primer walking method (Yamauchi 2002). Sequencing was performed

using Big Dye Ready Reaction Kit protocols (Applied Biosystems, Inc., Foster City,

CA). Sequencing reactions were run on an ABI3730 capillary sequencer at the MGS;

PCR and primer sequences are given in Table 4.1. The sequences generated were

then manually edited, assembled and annotated using Sequencher 4.1 (GeneCodes

Corporation, Ann Arbor, MI) and Geneious 7.1.6 (Drummond et al. 2012).

4.2.3 Illumina sequencing of three frog genomes

Total genomic DNA (1-2ug) was extracted from muscle and toe tissue of C.

vitianus (Taveuni), C. vitiensis and Hylarana kreftii using a Roche high pure

purification kit (https://lifescience.roche.com/shop/products/high-pure-pcr-template-

preparation-kit). Illumina TrueSeqTM libraries were then prepared by the Massey

Genome Service (MGS) and sequenced on their Illumina GAIIx platform. Reads

were then quality checked and trimmed (p=0.05) using SolexaQA scripts

(http://solexaqa.sourceforge.net/; Cox et al. 2010).

60

Table 4.1 Primers used to amplify the Fijian Cornufer Mitogenomes.

No Primer Name Taxonomic Scope Sequence (5’ -3’) 1 HS1108R12SRNA Vertebrates AGTGTGCTTGATACCCGCTCCT 2 FFcytbF1 C. vitianus only CTTCTTCCTTTTATGCTTGC 3 Av1861R12S Vertebrates TCGATTATAGAACAGGCTCCTC 4 FF12SR1 Both Fijian frogs TTTGCGACAGGGACGGGTTT 5 Av1753F12S Vertebrates AAACTGGGATTAGATACCCCACTAT 6 FF16SR2 Both Fijian frogs CCTTCTCTGCCTTTTAATCTTTC 7 Av3782R16S Vertebrates CGGTCTGAACTCAGATCACGTA 8 FF16SF3 Both Fijian frogs GAAGACACTATGCTTGAAC 9 FFND1F2 Both Fijian frogs CCCCCTTCCCATACCAACCCCC

10 FFND1R1 Both Fijian frogs GGTAAATAGGGGTTGTGATGG 11 FFCR1R1 Both Fijian frogs AAGCTAGTGGGCCCATCCCCC 12 FFCR1R2 Both Fijian frogs AGCAGGACTCGAACCTGCACTCA 13 FFND1F2a Both Fijian frogs TCCTGGCCTCAGGGTGAGCA 14 FFND1F1 Both Fijian frogs ACATCTCCATTCCCACCTCCC 15 FFND2Fa Both Fijian frogs TGCCCCATTAACCCTCCTCTTAC 16 FFND1F2c Both Fijian frogs CGGGCAATTGGTCAAACACGGG 17 FFCO1R2 Both Fijian frogs TGGTAGAATAAGAATATAAAC 18 FFND2Fb2 Both Fijian frogs AGCTTTAACACCACCAGAACCT 19 FFND2Fb1 Both Fijian frogs GAAAATTTCGACCAAAATCGCGAGGT 20 FFCO1F4 Both Fijian frogs ACTCGCTGATTCTTATCCACAAACCAC 21 FFND2F3 Both Fijian frogs CTCGCTGATTCTTATCCACAAACCACA 22 FFCO1R1 Both Fijian frogs AGAGGTGTTGATAGAGGATTGG 23 CO1gapR Both Fijian frogs AACCCGGAGCCCTACTGGGG 24 CO1gapR2 Both Fijian frogs GGGGCCGGAACAGGCTGAAC 25 FFCO1R3 Both Fijian frogs TATGCTGTGGGCACTAGGCT 26 FFCO1R4 Both Fijian frogs CACCTTCTTTGATCCGGCGGGG 27 FFCO1F2 Both Fijian frogs CCAATCCTCTATCAACACCTC 28 FFCO2R1 Both Fijian frogs GCATGAAGCTGTGGTTTGCCCC 29 FFCO1F3 Both Fijian frogs GGCCTCGTCAGCAGGCTCTC 30 FFCO3R3 Both Fijian frogs CACCCACCACCCAACTATCACT 31 PlatyCO3R Both Fijian frogs GAGAGAGTACATTTCAAGGACACC 32 PlatyCO3F Both Fijian frogs CAACCCCAGCCCATGACCACTT 33 FFtGlyF Both Fijian frogs TGGCCTCGACTAGCCCCGAG 34 FFND4LF Both Fijian frogs CAGCCCGGTCACAAGGCACC 35 FFND4F1 Both Fijian frogs GAGGCCCCAGTAGCAGGATCA 36 FFND4F1a Both Fijian frogs TCTCCCAATTTTCCTTGATCGCAAACT 37 FFND5R2a Both Fijian frogs AGCACCATGGTCGTAGCGGGA 38 FFND5R2 Both Fijian frogs CCACAACATCAACCCTGGCAGCA 39 FFND5R Both Fijian frogs TCAACCCTCCTCGCCGCCTC 40 FFND6R Both Fijian frogs CCCCCGCCTCAAACTAAGCGC 41 L14850F Anura TCTCATCCTGATGAAACTTTGGCTC

61

From these data, contigs were assembled using Velvet (Zerbino and Birney

2008) and the relative read coverage of contigs was used to distinguish nuclear and

mitochondrial genome sequences. This was possible because of the much higher

copy number of mitochondrial genome sequences in comparison to nuclear genomes

sequences. This assembly of contigs was made by the MGS’s bioinformatics team

(Leslie Collins and Bennet McComish). Some gaps remained at the end of the

assembly process and these were closed using short range PCR and Sanger

sequencing using the ABI3730 protocol described previously. Annotations to the

assembled mitochondrial genomes were made using Geneious 7.1.6 and the

programmes therein. Accession details for the four sequenced frogs and those

downloaded from GenBank can be found in Appendix .A.

4.2.4 Taxon sampling from GenBank genome sequences

Three salamanders and 40 anuran mitochondrial genomes were downloaded

from GenBank (Appendix A). The taxa selected are broadly representative of the 53

currently extant anuran families. The three newly sequenced genomes of the three

Fijian species and a fourth from Hylarana kreftii were added to the 43 taxon set from

GenBank. Two concatenated datasets were compiled comprising i) 18 tRNAs (Val,

Leu, Ile, Gln, Met, Trp, Ala, Asn, Cys, Tyr, Ser, Asp, Lys, Gly, Arg, His, Ser, Glu)

and the 12S and 16S rRNAs and ii) 12 protein coding genes (ND6 was excluded as it

is encoded on the heavy mitochondrial DNA strand (Gibb et al. 2007).

4.2.5 Sequence alignments and data partitions

Some taxa had missing tRNA and protein genes; these sites were coded as

missing data. Protein encoding genes were analysed separately from the RNA

encoding genes. Sequences were aligned initially in Sequence Alignment Editor

V2.0a11 (Se-AL) (http://evolve.zoo.ox.ac.uk) and then in G-Blocks using default

parameters, to remove regions of dubious alignment (Catestrana 2000; Talavera and

Catestrana 2007). All third codon positions of the protein-encoding sequences were

excluded using MEGA 6.0 (Tamura et al. 2013) after aligning the homologous

regions, because some genes have incomplete stop codons (Irisarri et al. 2012;

Kurabayashi et al. 2013) and to reduce the effect of substitution saturation (discussed

in Chapter 6). Resulting alignments were trimmed using a generic document editor

then the edited nexus files were realigned and checked by translation in Geneious

62

7.1.6 (Drummond et al. 2012). The final sequence lengths for the edited

concatenated protein coding genes and RNA datasets were 6272 bp and 3391 bp

respectively.

4.2.6 Phylogenetic reconstruction

4.2.6.1 PHYML trees

Individual gene datasets were run on jModelTest 2.1.4 (Darriba et al. 2012)

to determine the most appropriate model of molecular evolution (Zhang et al. 2013)

under the Akaike Information Criterion (AIC) and Bayesian Information Criterion

(BIC). These are models showing greatest improvement in fit to the data with as few

parameters as possible (see Appendices 3 and 4 for the consensus networks of

alternative tree topologies from the jModelTest output for the concatenated protein

coding geness and RNA datasets). Maximum likelihood trees for the concatenated

and individual protein coding genes were constructed using PhyML 3.1(Guindon et

al. 2010). Tree searches assumed the best of NNI (nearest neighbour interchanges)

and SPR (sub-pruning and re-grafting) branch swapping, and optimal substitution

model parameters. 100 bootstrap replicates were made for each data set.

Bootstrap PhyML trees were summarised using consensus networks built

with Splitstree 4.13.1 (Huson and Huson 2006). Optimal PhyML trees were edited

and visualised using FigTree 1.4.1 (http://tree.bio.ed.ac.uk/software/figtree/).

Phylogenetic diversity (PD; Faith 1992) values were calculated in Splitstree to

estimate the relative proportions of the overall tree length comprising of

Neobatrachian and Archaeobatrachian frogs respectively. PD values (%) for each

gene were tested for goodness of fit (χ2 coefficient) where H0 was PD (gene) % =

50%.

4.2.6.2 Divergence time estimates

Divergence time estimates were made in BEAST 1.8 (Drummond et al. 2012)

to estimate divergence times. Three calibration points were used as priors for

divergence times using a lognormal distribution of prior probability (from Irisarri et

al. 2012; data derived from Lisanfos KMS V1.2):

1) Anura-Caudata split: Offset=249 mya from the minimum fossil age for

Triadobatrachus (Rage and Rocek 1989); log mean=3.7; log SD=0.351.

63

2) Branching of Discoglossoidea: Offset=161.2 mya from the first known

Discoglossoid, Eodiscoglossus (Evans et al. 1990); log mean=3.6; log SD=0.532.

3) Branching of Pipoidea: Offset=145.5 mya as the minimum fossil age for

Rhadinosteus, putatable first Pipoid (Henrici 1998); log mean=3.45; log SD=0.668.

Separate analyses were performed on the protein coding gene and RNA

datasets with the final Markov chain running for 10 million generations, sampling

every 1000 generations with the first 1,00,000 generations discarded as burn-in. The

Yule process was assumed and independent GTR+I+G models were applied for the

concatenated data partitions. Substitution model parameters were estimated by

BEAST. Convergence of the Markov chains was monitored a posteriori using

Tracer 1.6 (Rambaut and Drummond 2009).

4.3 RESULTS

4.3.1 Mitochondrial gene order in Fijian frogs

The genomic arrangements of C. vitiensis and C. vitianus were similar

(Figure 4.1), with both species exhibiting a unique rearrangement as yet undescribed

for Neobatrachian frogs (Figure 4.1). The control region (CR), along with the site of

initiation for replication of the leading or heavy strand of the circular genome (OH),

is translocated between ND2 and COI followed by a rearranged WANCY cluster

(current order is tRNAAla – tRNATyr – tRNACys – tRNAAsn). There is a loss of

tRNAThr in the C. vitianus genome but not so in the C. vitiensis genome where

tRNAThr has translocated to within the tRNAIle -tRNAGlu-tRNAMet cluster.

In both species tRNATrp is deleted and tRNAMet has been duplicated, and both

copies of tRNAMet appear to be functional (in terms of sequence order and size). In

C. vitianus (and the Taveuni frog), the duplicated tRNAMet genes are adjacent to each

other. Whereas in the C. vitiensis genome, the rearranged gene order in that tRNA

cluster is tRNAGlu – tRNAMet(1) – tRNAThr – tRNAIle – tRNAMet(2). In both species’,

tRNAHis has translocated between tRNALeu and tRNAPro where tRNAThr is located, as

in the standard Neobatrachian gene order.

4.3.2 Phylogenetic relationships recovered

The analysis of RNA and protein coding gene datasets yields similar tree

topologies among basal groups recovered in previous studies (Appendices 2-3).

Significant congruence existed between the optimal PhyML trees and the consensus

64

network derived from bootstrap replicates (Figures 4.2 and 4.3). An exception

concerned the ML phylogram (Figure 4.2b) for the mitochondrial RNA dataset

which assigned the Pelobatoidea taxa (Leptolalax pelodytoides and Pelobates

cultripes) as sister to the Bombinanura (Discoglossus galganoi, Alytes obstetricans

pertinax, Bombina orientalis). In contrast, the protein coding gene ML phylogram

recovered the relationship inferred in previous studies; i.e. Bombinanura as sister

taxa to Pipanura.

Relationships within the Neobatrachia showed greater difference between

protein coding gene and RNA data sets, consistent with the uncertainty expressed by

bootstrap support values in earlier studies (Irissari et al. 2012, Kurabayashi et al.

2010; Kuruyabashi and Sumida 2013); and this may be related to taxon sampling in

this species-rich branch of the anuran tree of life. The phylogram based on the

protein coding gene dataset recovered the same branching pattern as in Zhang et al.

(2013) and Kurayabashi and Sumida (2013), between the two superfamilies Hyloidea

and Ranoidea and the Sooglossidae (an intermediate branch between the two

superfamilies with Sooglossus thomasseti as sister taxa to the Ranoidea). In the RNA

ML tree this relationship was recovered but the Sooglossidae was placed as basal to

the Hyloidea and Ranoidea.

Within the family Hyloidea, branch support was low in the shallower nodes

of the protein coding gene dataset but stronger with the RNA dataset. In the protein

coding genes tree, Dendrobatidae was basal to the rest of the Hyloidea but in the

RNA tree Eleutherodactylidae was basal. There are further discrepancies within

Hyloidea, which may be reflected in the low branch support for several of the

groupings within both the protein coding genes and the RNA trees. In the protein

coding genes tree, the Hemiphractidae was basal to a clade comprised of the

Bufonidae, Centrolenidae, Odontophrynidae, Ceratophryidae and the Hylidae.

However, the RNA tree recovered a similar branching pattern as observed in

previous studies (Kurayabashi and Sumida 2013) – where the Hemiphractidae and

the Ceratophryidae are sister taxa and there is a stepladder-like pattern from the

Hylidae to the Odontophrynidae, then the Bufonidae and the Centrolenidae. In the

Ranoidea, the Pyxicephalidae (Tomopterna cryptotis) was basal to the other families

as expected from the literature.

65

Figu

re 4

.1 M

itoch

ondr

ial g

enom

e or

gani

satio

n fo

r the

thre

e Fi

jian

frog

taxa

Cor

nufe

r viti

ensi

s, C

. viti

anus

, and

C. v

itian

us (T

aveu

ni).

66

Table 4.2a Optimal Models for Individual Genes and Concatenated Datasets.

Gene

Best Model Selected Under Criterion Applied

AIC BIC DT Model Applied

in PhyML Analysis

Cytb TVM+I+G TVM+I+G TVM+I+G TVM+I+G

p-inv 0.3290 gamma

0.4590 p-inv 0.3290

gamma 0.4591 p-inv 0.3290

gamma 0.4592 ND1 GTR+I+G TIM2+I+G TIM2+I+G TIM2+I+G

p-inv 0.1870 gamma

0.3740 p-inv 0.1710

gamma 0.3530 p-inv 0.1710

gamma 0.3531 ND2 GTR+I+G GTR+I+G GTR+I+G GTR+I+G

p-inv 0.1640 gamma

0.5890 p-inv 0.1640

gamma 0.5891 p-inv 0.1640

gamma 0.5892 CO1 TIM1+I+G TIM1+I+G TIM1+I+G TIM1+I+G

p-inv 0.4020 gamma

0.3130 p-inv 0.4020

gamma 0.3130 p-inv 0.4020

gamma 0.3131 CO2 GTR+I+G TPM2uf+I+G TPM2uf+I+G TPM2uf+I+G

p-inv 0.2480 gamma

0.4030 p-inv 0.1670

gamma 0.3090 p-inv 0.1670

gamma 0.3091 CO3 TPM2uf+I+G TPM2uf+I+G TPM2uf+I+G TPM2uf+I+G

p-inv 0.2270 gamma

0.2610 p-inv 0.2270

gamma 0.2611 p-inv 0.2270

gamma 0.2612 ATP6 TrN+I+G TrN+I+G TrN+I+G TrN+I+G

p-inv 0.2100

gamma 0.5250 p-inv 0.2100

gamma 0.5250 p-inv 0.2100

gamma 0.5250 ATP8 TIM2+G HKY+G HKY+G TIM2+G

p-inv - gamma

0.4720 p-inv -

gamma 0.4870 p-inv -

gamma 0.4871 ND3 TPM2uf+I+G TPM2uf+I+G TPM2uf+I+G TPM2uf+I+G

p-inv 0.2510 gamma

0.4540 p-inv 0.2510

gamma 0.4541 p-inv 0.2510

gamma 0.4542 ND4L TVM+I+G TVM+I+G TVM+I+G TVM+I+G

p-inv 0.1270 gamma

0.3350 p-inv 0.1270 gamma 0.3350

p-inv 0.1270 gamma 0.3350

ND4 GTR+I+G TIM2+I+G TIM2+I+G GTR+I+G

p-inv 0.1560 gamma

0.6090 p-inv 0.1550

gamma 0.6070 p-inv 0.1550

gamma 0.6071 ND5 GTR+I+G TIM2+I+G TIM2+I+G GTR+I+G

p-inv 0.0890 gamma

0.5480 p-inv 0.0880

gamma 0.5500 p-inv 0.0880

gamma 0.5501 Concatenated

protein coding genes

TVM+I+G TPM2uf+I+G TPM2uf+I+G TVM+I+G p-inv 0.4440 gamma

0.8040 p-inv 0.4440

gamma 0.8040 p-inv 0.4440

gamma 0.8041

Concatenated RNAs

GTR+I+G GTR+I+G GTR+I+G GTR+I+G p-inv 0.2330 gamma

0.6790 p-inv 0.2330

gamma 0.6791 p-inv 0.2330

gamma 0.6792

67

Table 4.2b. Phylogenetic Diversity of Neobatrachians in PhyML Trees.

Gene Model of Substituion Rate PD Estimate Cytb TVM+I+G 17.082203 (70.1%) ND1 TIM2+I+G (BIC) 13.004617 (73.3%)* ND2 GTR+I+G 19.944754 (69.4%) CO1 TIM1+I+G 44.490326 (74.8%) CO2 TPM2uf+I+G (BIC) 22.707685 (75%)# CO3 TPM2uf+I+G 22.707685 (75%)# ATP6 TrN+I+G 20.40861 (73.1%) ATP8 TIM2+G (AIC) 13.004617 (77.7%) ND3 TPM2uf+I+G 19.944754 (69.4%) ND4L TVM+I+G 19.224018 (69.4%) ND4 GTR+I+G (AIC) 20.40861 (72.5%) ND5 GTR+I+G (AIC) 19.224018 (72.2%) Concatenated protein coding genes TVM+I+G (AIC) 6.8950915 (79.1%)

Concatenated RNAs GTR+I+G 8.474362 (65.9%) Average = 19.109 (72.64%)

* Leptolalax pelodytoides excluded {when included PD = 18.179806 (65.1%)] # Eleutherodactylus atkinsi excluded [when included PD = 18.898283 (67.7%)]

68

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72

The two clades internal to the Pyxicephalidae were comprised of an upper

branch (Mantellidae, Rhacophoridae and Ranidae) and a lower branch

(Phrynobatrachidae and Dicroglossidae). In the RNA tree, the Fijian frogs were

sister taxa to the Mantellidae and Rhacophoridae. In contrast, in the protein coding

genes tree, the Fijian Cornufer taxa were recovered basal to the Ranoidea. Other

branches within the Ranoidea recovered expected relationships between adjacent

terminal taxa.

4.3.3 Molecular evolution of Neobatrachian mitochondrial genomes

It was a point of interest to determine whether different mitochondrial genes

were described by different models of substitution and having determined the most

appropriate substitution model, to estimate the relative branch lengths of

Archaeobatrachian and Neobatrachian frogs. Table 4.2a indicates that optimal

substitution models for different genes were similar (see Appendix B and C for

consensus network of model trees), typically special forms of the Generalized Time

Reversible (GTR) model with gamma and a proportion of invariable sites estimated

(GTR+I+G). Table 4.2b shows estimates of relative Phylogenetic Diversity (PD;

Faith 1992) calculated on PhyML trees built from the optimal substitution models.

PD values here are directly comparable with the estimates of substitution rate used

by Irisarri et al. (2012), who also studied substitution rate acceleration in

Neobatrachians. The values shown in the table indicate that the lineage specific rate

heterogeneity observed in our concatenated gene trees, and previously reported by

others (e.g. Hoegg et al. 2004; Igawa et al. 2008; Kurabayashi and Sumida 2013), is

characteristic of all the protein encoding protein coding genes in the mitochondrial

genome.

4.3.4 Divergence time estimates for Fijian Frogs

For the reasons discussed below, the concatenated protein coding gene and

RNA datasets are likely to provide an upper bound (estimate) for divergence time

estimates of Fijian frogs (Figures 4.3a and 4.3b). Using priors on the three fossil

(Triadobatrachus, Eodiscoglossus, and Rhadinosteus) calibrations from earlier

published work (Irisarri et al. 2012; Lisanfos KMS V1.2) we estimate that

divergence of C. vitianus and C. vitiensis occurred between 23 – 59 ma (95% HPD

73

38.7 – 74.5 ma RNA data set; 95% HPD 23.5 – 58.9 ma protein coding genes data

set).

This analysis also suggested a divergence time between the Taveuni

mitochondrial haplotype and the predominant ground frog haplotype (found

elsewhere) at 10 – 30 ma (95% HPD 8.4 – 33.2 ma RNA data set; 95% HPD 4.6 –

26.9 ma protein coding genes data set; Figures 4.3a and 4.3b).

4.4 DISCUSSION

4.4.1 Molecular evolution and phylogeny of Anuran mitogenomes

Optimal substitution models were determined for each individual gene and

concatenated genes. These models were found to be relatively similar and the

PhyML trees were built using the optimal substitution model for each gene. Trees for

both of the concatenated datasets (protein coding genes and RNAs), suggest

significant rate heterogeneity between Neobatrachian and Archaeobatrachian frogs.

Similar observations on the molecular evolution of Anuran mitochondrial genomes

have been made previously (Irisarri et al. 2012; Kurabayashi and Sumida 2013;

Zhang et al. 2013) and a number of hypotheses have been advanced to explain the

apparent speed up in the rate of molecular evolution of Neobatrachian frogs. These

hypotheses concern relaxation of purifying selection in Neobatrachian mitogenomes

(Hofman et al. 2012; Kurabayashi and Sumida 2013) possibly due to changes in life

history traits and metabolic rates in Neobatrachian lineages (Irisarri et al. 2012).

Although Irisarri et al. (2012) show substitution rate heterogeneity amongst

mitochondrial genes in anuran genomes, the PD values in Table 4.2b suggest that this

inherent mutational bias does not affect the resulting outcome: Neobatrachians are

generally more divergent than Archaeobatrachians even when considering single loci

independently. One of the a priori hypotheses tested was that genes adjacent to

regions of structural plasticity in anuran mitogenomes (e.g. genes surrounding the

control region or the WANCY hotspot: ND5, cytb, ND1, ND2 and CO1,

respectively) would show greater PD values than the mean PD (72.6%; Table 4.2b)

but there was no statistical support for this assumption (p<0.001(d.f=13), χ2 = 13.0).

74

Figure 4.4a Dated BEAST chronogram for the 47 taxa mitogenome concatenated

protein coding genes dataset.

75

Figure 4.4b Dated BEAST chronogram for the 47 taxa mitogenome concatenated

tRNA and rRNA dataset.

76

Table 4.3. Highest Posterior Density (HPD) Values from BEAST 2.0.

Divergence/ Splits 95% HPD Interval Mitochondrial protein coding genes Upper (ma)

Lower (ma)

Anura and Caudata 263.7 299.9 Disglossoidea 174.6 238.4 C. vitianus and C. vitiensis 23.5 58.9 C. vitianus (Taveuni) 4.6 26.9 Pelobatoidea-Neobatrachia 151.4 214.5 Pipoidea 164.3 227.6

RNA Upper (ma) Lower (ma)

Anura and Caudata 263.5 300.7 Disglossoidea 181 244.6 C. vitianus and C. vitiensis 38.7 74.5 C. vitianus (Taveuni) 8.4 33.2 Pelobatoidea-Neobatrachia 155.2 220 Pipoidea 160.2 224.1

77

Currently there is considerable discussion in the literature concerning the

nature of organelle genome molecular evolution and the relationship of substitution

rates to indels and gene rearrangements (e.g. Ahmed et al. 2012). In plastid genomes,

elevated substitution rates appear to mostly concern genes located adjacent to points

of structural rearrangement (such as inversion endpoints) or expansion and

contraction (such as the junction of the single copy and inverted repeat boundaries).

The relative location of genes showing elevated mutation rates in Anuran

mitochondrial genomes has not been definitively addressed in the literature.

Although a correlation between gene rearrangement and substitution rate has

been suggested for invertebrate taxa (Shao and Baker, 2003) the nature of the

relationship in Anurans is unclear. Previous observations suggest that accelerated

base changes are not statistically linked to the occurrence of rearrangements amongst

lineages; neither is rate acceleration significantly different between rearranged/

duplicated genes and standard genes (Kurabayashi and Sumida 2013). The

conclusion of several similar studies is that phylogenetic inferences based on

mitogenomes can be reliably made despite rate heterogeneity (Macey et al. 1997;

San Mauro et al 2005).

4.4.2 Phylogenetic reconstruction with anuran mitogenomes

Regardless of the exact nature of the relationship between genome evolution

and substitution rate, the acceleration of evolutionary rates in Neobatrachian

sequences has implications for phylogenetic inference, and in particular divergence

time estimates for the diversification of Fijian frogs. In other words the calibration of

fossils with sequence divergence of Archaeobatrachian frogs, could potentially lead

to the overestimation of temporal estimates of divergence between Neobatrachian

frogs, as accelerated rates in lineages of the latter could suggest older divergence

times than has actually been the case. The reverse could also be true, in that

divergence within the Archaeobatrachia could be under-estimated. A lack of fossil

calibration points closer to the divergence of Ranoidea limits the accuracy of

divergence time estimates (as noted by Bossuyt et al. 2006).

That said, it is important to note that relationships inferred in PhyML and

BEAST phylogenetic reconstructions for our concatenated RNA and protein coding

gene data sets give similar results to those found in earlier studies. Previous

reconstructions using nuclear and mitochondrial markers report moderate bootstrap

78

support (50 - <95%) for their placements of Ceratobatrachidae (Bossuyt et al. 2006;

Roelants et al. 2007; Pyron and Wiens 2012; Barej et al. 2014). Consistent with our

findings, recent reconstructions of Ranoidea phylogeny also place the

Ceratobatrachidae as most closely related to frog taxa from the families

Rhacophoridae, Mantellidae and Dicroglossidae (Bossuyt et al. 2006; Roelants et al.

2007; Weins et al. 2009; Barej et al. 2014).

With greater taxon sampling earlier large scale anuran reconstructions have

placed Ceratobatrachidae as sister taxa to (i) the Nyctibatrachidae (Pyrons and Wiens

2011; 2871 species); (ii) a clade comprising Ranidae, Dicroglossidae, Mantellidae,

Rhacophoridae and Nyctibatrachidae (Bossyut et al. 2006; 104 species); or, (iii) a

clade comprising of the Nyctibatrachidae, Mantellidae and Rhacophoridae (Weins et

al. 2009). In another large scale reconstruction (Roelants et al. 2007; 171 species)

using a concatenated mitochondrial (16S RNA) and nuclear gene (CXCR4, NCX1,

RAG1, SLC8A3) dataset, the Nyctibatrachids are placed as the sister taxa to a clade

comprising of the Dicroglossidae, Ceratobatrachidae, Ranidae, Rhacophoridae and

Mantellidae. The incongruence between mitogenomic and nuclear gene trees (seen

in Figures 4.2, 4.3 and 4.4) is likely due to conflicting individual genealogies

(evolutionary gene tree histories) which can result from differences in the lineage

sorting of nuclear and mitochondrial genomes (Brown Pers. comm. 2015).

4.4.3 Taxonomic implications from sequence analyses

Three features of earlier published phylogenetic analyses have particular

relevance for relationships concerning Fijian Ceratobatrachids:

(1) There is a strong indication (based on bootstrap support) that the

Ceratobatrachid lineages as previously recognized, are paraphyletic. The recent

revision of the family by Brown et al. (2015) has seen major changes and a clearer

tree structure evolve within the family (minimal paraphyly). The Fijian frogs have

been placed within the resurrected genus Cornufer, along with other non Southeast

Asian members of the family (from Discodeles, Ceratobatrachus, Batrachylodes,

Palmatorappia and Platymantis). The taxonomic name changes of the recent review

will likely evolve with time. However, it is probable that the Fijian frogs will remain

as a sub-clade (sub-genus) within the genus Cornufer.

(2) The phylogenetic support for the relationships within the Ranoidae

(including the placement of the family Ceratobatrachidae) is not robust and the

79

placement of families is subject to model and methodological ssumptions used in

these analyses. Nevertheless, most studies agree on which anuran families belong to

this superfamily.

(3) The sister relationship between Sooglossidae and Ranoidea (Ranoides)

described in recent phylogenetic treatises is shown in our protein coding genes ML

tree but not our RNA tree. However, in the RNA tree there is maximum bootstrap

support for placing Sooglossidae as basal to the other Neobatrachian lineages,

compared to the protein coding genes tree where bootstrap support is approximately

50%. The uncertainty in this placement can be visualised readily in the consensus

network splitsgraphs where the only lack of resolution (or boxy-ness) occurs at that

node (the divergence between Sooglossidae, Hyloidea and Ranoidea). This lack of

resolution is apparent in the splitsgraphs for both the mitogenome protein coding

genes and RNA datasets (Figures 2.3a and 3.3a respectively).

The level of uncertainty can be further identified by the height or ‘boxy-ness’

of that split, which is more pronounced in the RNA graph compared to the protein

coding genes graph. Congruence of the placement of Sooglossidae in recent papers

should therefore be treated with caution, and may speak more to the similarity in

treatment of the GenBank sequences than to the accuracy of this inference.

4.4.4 Divergence of Cornufer spp. based on mitogenome sequences

A dated chronogram was obtained for concatenated mitochondrial genomes

including three new mitochondrial genomes determined in the present work. In the

case of the concatenated protein coding genes data set, the phylogenetic signal of

individual genes was also examined. Our chronogram for the 44 frog taxa analysed is

constrained by the same fossil calibrations as other anuran studies of this scale but

we have used fewer calibration points (described in Section 4.2.6.2) than other large

scale treatises (e.g. Bossuyt et al. 2006). However, our starting trees differed based

on the dataset used, and the BEAST analysis was directed by the model of molecular

evolution inferred from these datasets by jModelTest. There is a disparity in the

estimation of divergence using the molecular evolution of RNA sequences compared

to protein coding genes. It has been suggested in previous studies that mitochondrial

RNA genes are less affected by substitution saturation when compared to

mitochondrial protein encoding genes, and thus do not overestimate divergence times

as much as protein coding gene trees. For this reason, inferences based on rRNA

80

analyses have been favoured by some authors for deep phylogeny reconstructions

(Zheng et al. 2011).

The RNA tree sets the divergence of Fijian frogs from the rest of Ranoidea at

144 ma whereas the BEAST tree derived from the protein coding genes sequences

suggests an older data of 178 ma. Previous temporal estimates of diversification

within the super-family date the last shared common ancestor of Ceratobatrachids

and sister taxa as approximately (i) 65 ma (Roelants et al. 2007); (ii) 85 ma (Weins et

al. 2009); and, (iii) 95 ma (Bossuyt et al. 2006). These earlier studies used Bayesian

methods of dating on datasets comprising of both nuclear and mitochondrial genes

(mostly protein or RNA encoding). These temporal estimates of crown group ages

are younger than our RNA tree estimates of the Fijian frog divergence which might

suggest that unquantified substitution saturation across the whole mitochondrial

genome has led to the overestimation of divergence times. Divergence between the

two extant species of Fijian Ceratobatrachids is between 82 ma (from the RNA tree)

and 91 ma (from the protein coding genes tree).

Both the protein coding genes and RNA analyses arrive at the same temporal

estimate of 26 ma for the divergence of the Taveuni population from other ground

frogs. This time estimate predates the hypothetical emergence of Taveuni (based on

geological evidence) since the Holocene (Neal and Trewick 2008), and suggests an

older origin for the genetically distinct Taveuni C. vitianus. In Chapter 5, nuclear

markers were used to estimate divergence of the Taveuni frogs and the analyses

suggest an estimate of between 10.6 and 30.3 ma. This time range also predates the

emergence of Taveuni Island (~3 - 3.5 ma; Chronin and Neal 2001). It is plausible

therefore that during glacial maxima the oceanic gap (the Somosomo Strait) between

the Natewa/ Tunuloa Peninsula and Taveuni was only several kilometres wide and

therefore easier to disperse across.

Although the confidence we can place in time tree chronology is really only

as high as the confidence we have in the fossil placements on our reconstructed

phylogeny, these calibrations provide only one third of the information used by

BEAST to derive chronograms (Drummond and Remco, In prep.). The rest of the

information lies in the differential rate substitution between taxa on the time tree and

that data are fairly objective. The lack of congruence between the RNA tree and the

protein coding gene tree, in terms of the placement of the Fijian Ceratobatrachid

branch within Neobatrachia, is mirrored in the optimal bootstrapped ML trees. This

81

is likely to affect the two time estimates for divergence, as the estimates will be

based on the most nearest common ancestor as perceived in the nucleotide alignment.

We may assume then that Phrynobatrachus keniensis is not as closely related as

implied by the branch topology of the protein coding gene tree.

The age estimates of 82 – 91 ma for the split between the two extant Fijian

Ceratobatrachids predates the oldest known rocks on Viti Levu (which are between

40 – 36.5 my in age) by more than 40 ma of geological history (Neall and Trewick

2008). Geological reconstructions place an ancestral Viti Levu landmass within a

chain of islands to the east of Australia (the Melanesian/ Vitiaz Arc system) as recent

as 40 ma (Yan and Kroenke 1993; Evenhuis and Bickel 2005). Tectonic breakup of

the island arc resulted in Fiji being closest to the New Hebrides archipelago

(Vanuatu) about 10 ma. Both Vanuatu and Fiji have flora with gondwanic relicts;

gymnosperms such as Dacrydium and Agathis and an ancient angiosperm family, the

endemic Degeneriaceae. However, Ceratobatrachid frogs did not apparently

colonise islands south of the Solomon Islands.

The movement of the Fiji plate from its position within the Melanesian Arc to

its current location in geological reconstructions (Hall 1996), i.e. the “rafting island”

theory, and the possibility that it may have carried a Cornufer individual(s) are valid

hypotheses to consider. It is plausible that the Fijian Ceratobatrachids may have

evolved within the Vitiaz arc system and these ancestral frogs have since gone

extinct elsewhere in their prehistoric range. Additionally, a hypothesis that the

ancestral Cornufer populations on the “island raft” survived tectonic displacement

and subsequently diverged is also plausible. If so, this would presumably require a

diversification process that is likely to have been driven by natural (adaptive)

selection pressures acting on the founding population (Glor 2010). However, if our

age estimates are indeed exaggerated by mitogenome substitution saturation and/or

model misspecification, then there might be closer convergence in the molecular

divergence time estimates and the periods during which colonization was more likely

(i.e. younger divergence estimates coinciding with the formation of emerged land in

the Miocene).

Dispersal of anurans along the Melanesian Arc during the Miocene would

possibly have resulted in rapid adaptive radiations to fill available niche spaces as

suggested for the Philippine ceratobatrachid frogs (Blackburn et al. 2013). It is

noteworthy that a recent avian study has suggested that dispersal may have hindered

82

diversification in Australasian archipelagoes (Weeks and Claramunt 2014). This

could be the case where dispersability of taxa is high (as it would be for winged

animals), and gene flow prevents divergence of allopatric populations. However,

anurans are poor dispersers. With these animals dispersal events historically are

expected to have been infrequent and often the result of extreme weather (cyclones,

floods, etc.). Thus dispersal in this instance might aid speciation either through (i)

the colonization of new habitats with different selective pressures driving adaptive

radiation; and/or because (ii) the geographic separation of previously contiguous

populations reduces gene flow, heightening allelic (genetic) drift and speeding up

reproductive isolation (Gavrilets and Losos 2009).

It is just as likely that an ancestral Cornufer species from Southeast Asia

dispersed through island Asia to the Sundaland island of New Guinea, down into the

Melanesian Arc islands (“island hopping”) and onto a putative Viti (Fiji) landmass.

The closest relative of the Fijian sub-genus Cornufer amongst the family is the Giant

webbed frog, C. guppy (sub-genus Discodeles; formerly D. guppyi) [Brown et al.

2015]. The Giant webbed frog is very distinctive in the family as its common name

indicates, due to its sheer size and inter-digital webbing. These phenotypic traits are

not shared with the Fijian sub-genus Cornufer. However, it is widespread

throughout the islands of Papua New Guinea, the Bismarks and the Solomons,

occupying a range of habitats similar to the Fiji ground frog, C. vitianus

(AmphibiaWeb 2015). A putative ancestral Cornufer would then have diversified

into the lineages present on the current landmasses in Melanesia (including Fiji).

This diversification would have been facilitated by lower extinction rates than

speciation rates (Weins et al. 2009; Weeks and Claramunt 2014). Although we

currently lack fossil evidence to elucidate the Fijian frog prehistory (Worthy Pers.

Comm. 2007) there are tell tale signatures of population history that can be gleaned

from the data, perhaps provide insights (next chapter).

83

CHAPTER FIVE

PHYLOGENETICS AND POPULATION STRUCTURE

84

5.1 INTRODUCTION

Phylogenetic reconstructions of insular species in this century have largely

been influenced by the domineering paradigms of mid-twentieth century

biogeography theory. The precepts of island size and distance from mainland source

populations have been indelibly applied to many a discussion in the plentiful

literature on phylogenetic studies of island species (Holland and Madfield 2002;

Roberts 2006; Lohman et al. 2011). However, it has become increasingly obvious

that many of these precepts do not apply very well to island endemics (Bisconti et al.

2011; Bisconti et al. 2013). Of considerable note are amphibian taxa with their well-

established physical limitations for long-distance dispersal and high rate of molecular

evolution and adaptation (Rog et al. 2013; Blackburn et al. 2013; Gonzalez et al.

2014).

Previously it was assumed that dispersal, as a mechanism for structuring

patterns of genetic divergence in amphibian populations, can be detected clearly if an

“isolation-by-distance” pattern can be discerned in the data. If so, then studies of

anuran taxa should provide evidence for vicariant forces shaping their respective

phylogeographic histories (Kelly et al. 2006). Yet there is just as much evidence in

the literature in favour of dispersal by anurans, particularly within island

archipelagoes throughout Southeast Asian and across the western Pacific Ocean

(Evans et al. 2003; Brown et al. 2010; Setiadi et al. 2011; Brown et al. 2013).

Several mechanisms for anuran dispersal within island archipelagoes have been

proposed including dispersal via rafting vegetation (Measey et al. 2007), often aided

by lower sea levels (otherwise known as “island hopping”; Gonzalez et al. 2014) or

by large storm events (Simmons and Thomas 2004); dispersal aided by human

migration (Brown et al. 2010; Blackburn et al. 2013); and the least likely event of

dispersal of eggs by an avian vector (Fahr 1993).

Understanding the genetic relationships between intra- and inter- island

populations of anuran amphibians is a means to assess the conservation potential of

species (Moritz 2002; Wan et al. 2004; Emel and Storfer 2012). Evaluations of

genetic distinctiveness are often contentious and the implementation of conservation

recommendations can be fraught with error (Morin et al. 2010). Despite these issues,

applications of population genetics and phylogeographic research are arguably the

best means of ensuring long term viability of endangered species (deSalle and

85

Amato 2004; Sanchez-Molano 2013), particularly for anurans (Beebee 2005). The

inferences from phylogenetic analyses are of great use in tropical biodiversity

hotspots where human modification of natural habitat for forestry and agricultural

purposes is alarming the conservation sector, policy makers and practitioners at all

levels (Benhin 2006; Lambin and Meyfroidt 2011).

Conclusions can be drawn about population connectivity and vice versa,

genetic isolation of populations (Hoffman and Blouin 2004; de Campos Telles et al.

2006; Richardson 2012); about population history and biogeography (Boulet and

Gibbs 2006; Gamble et al. 2008); identification of genetic diversity hotspots as focal

spots for conservation efforts (Bernado-Silva et al. 2012), including source areas for

translocation experiments (Hedrick 2014); as well as predictions of adaptive and

migratory climate change responses (McLachlan et al. 2007; Dawson et al. 2011).

Fast evolving gene regions are often used for phylogeographic analyses as high

substitution rates in genes allow researchers to draw stronger phylogenetic inferences

from sequence data.

Mitochondrial genes such as 12SrRNA, coding for the small ribosomal sub-

unit used in transcription of DNA, have been widely and successfully used as

molecular markers. Most nuclear protein coding genes studied to date typically have

been slower evolving and thus have often only been useful for the resolution of

phylogenetic relationships at deeper ancestral nodes. Nevertheless, given their

independence from mitochondrial markers, phylogenetic studies of taxa have sought

to incorporate both nuclear and mitochondrial markers (Roelants and Bossuyt 2005;

Bossyut et al. 2006; Wiens et al. 2009; Pyron and Wiens 2011; Brown and Siler

2013). With the advent of next generation sequencing and analysis protocols, not

only can we assemble whole mitochondrial genomes very rapidly and efficiently, but

we can also derive novel markers for both mitochondrial and nuclear genes. For

intra-specific research, this methodology makes possible whole mitogenome

comparisons to counter issues such as an inherent lack of phylogenetic resolution. In

the case of nuclear markers, both neutral and adaptive gene loci showing high levels

of sequence variation can be targeted (e.g. Becker et al. 2013).

Phylogeographic analyses today use both mitochondrial and nuclear

genotyping from populations or species to investigate the evolutionary and

demographic history of lineages within a species in a given geographical area

(Beheregaray 2008; Hickerson et al. 2010). Various methods for this purpose peaked

86

in use over the first decade of the 21st century following the rise in popularity of

phylogeographic research, than waned in popularity as newer approaches became

more available. This includes Templeton’s Nested Clade Phylogeographic Analysis

or NCPA (1998) which has now been superseded by probabilistic Bayesian

approaches (Lemey et al. 2009; Bloomquist et al. 2010). Statistical phylogeography

(Knowles 2004) has grown in popularity since the mid-2000s, especially in the past

five years by growth in ‘next generation sequencing’ (NGS) methodology and

applications (McCormack et al. 2013). Statistically guided geographic mapping of

genetic variation has expanded in application in recent years (Chan et al. 2011),

particularly as it is relevant to predicting species distributions given extant genetic

diversity, current distributions and anticipated global climate change scenarios

(Forester et al. 2013).

The Fijian archipelago is an ideal tropical “natural laboratory” to study the

evolution of genetic divergence in notoriously vulnerable or threatened anuran

species. Fiji was historically home to three Ceratobatrachid species that likely

occurred in sympatric populations: C. megabotonivitiensis, C. vitianus, and C.

vitiensis (Worthy 2001). Shifting forest habitat due to climate change as well as

predation pressure by humans and introduced species are probable causative agents

of extinction for C. megabotonivitiensis, and have likely influenced the disjunct

distribution of C. vitiensis and C. vitianus (Osborne, T. et al. 2013). Elucidating the

patterns of divergence and diversification on the islands that the Fijian frogs persist

on is therefore an imperative for conservation efforts and would be vital for guiding

management decisions.

In this chapter, phylogenetic relationships between the extant Fijian

Ceratobatrachid populations are examined and inferences about population history

have been made from resulting tree topologies, branch lengths and a Phylogenetic

Diversity (PD) metric (Faith, 1992) describing these features of reconstructed graphs.

Additionally, Bayesian inference to predict the most likely ancestral source

populations for ground and tree frogs have been made, and the rooted tree used as a

framework for interpreting population history and range expansion of both species.

Empirical and quantitative observations of five datasets, two mitochondrial and three

nuclear (developed using ‘reduced representation’ Illumina MiSeq NGS sequencing),

were used to reconstruct the phylogenetic relationships between island populations.

87

Although available data is insufficient to implement a statistical analysis that

can objectively distinguish between lineage sorting and hybridisation (Knowles and

Maddison 2006; Galtier and Daubin 2008; Yu et al. 2013; Joly 2012), observations

have been discussed that suggest diversification with gene flow is likely to have

accompanied divergence of ground frogs and tree frogs. The possibility of

hybridisation between C. vitianus and C. vitiensis is suggested from discordant tree

topologies, in particular concerning sympatric populations of Fijian frogs.

5.2 METHODS

5.2.1 Mitochondrial marker development and Sanger sequencing

DNA from individual frogs (Table 5.1) were extracted using extraction kit

protocols (Roche HighPure and Qiagen DNEasy) to derive sufficient tissue for

amplification (1-2μg). Universal avian and mammalian mitochondrial primers were

trialled in initial PCRs and success was variable. In our initial trials, avian and Harp

Seal primers that successfully amplified fragments of C. vitianus, did not produce

amplification products with C. vitiensis samples. PCR thermocycling profiles used

were standard short programmes: 94°C for 3 mins, 94°C for 30 secs, 50°C for 30

seconds (for 35 cycles), 72°C for 30 seconds with a touchdown of 72°C for 5 mins

and 4°C to hold. Fragments that were successfully sequenced off C. vitianus DNA

were a partial cytb, partial 12S rRNA, partial 16S rRNA, and two longer fragments

from cytb to 12S, and cytb to 16S. Primers were designed using OLIGO 6.0

(Rychlik 2007) and the species-specific primers were tested against a sub-sample of

frogs from 29 of the 32 populations surveyed on the six islands (refer to Chapter 3

Figure 3.1). Specific primers for C. vitiensis were likewise developed from large

amplicons generated by long PCR (described in Chapter 4). Species specific primers

were used to sequence DNA from at least 40 of the 54 frog DNA extractions listed in

Table 5.1. PCR products were cleaned using Big Dye kit reactions and sequenced on

an ABI 3730 capillary sequencing machine.

5.2.2 Nuclear marker development - reduced representation Illumina sequencing

Total frog genomic DNA from ground (Taveuni, Viti Levu and Viti Levu)

and tree frogs (from Viti Levu; 3 samples in total) were extracted using Roche High

Pure Kit protocols. The extracted DNA samples were digested and size fractions

~300-600 bp were collected on a 1% agarose. The fractions were then ligated with

88

Illumina indexed adaptors and sequenced in a single lane of the Massey Genome

Service Ilumina GAIIx™ platform. The resulting reads were 100 bp in length.

These were quality trimmed using SolexaQA (Cox et al. 2010) and contigs for each

taxon were generated from these reads using Velvet 1.0 (Zerbino and Birney 2008).

Orthologues were identified and clustered using OrthoMCL (Li et al. 2003) to

produce multiple sequence alignments, and these were filtered to retain only

alignments with highly similar sequences from ground frog and tree frog

populations. These analytical steps were performed by bioinformaticians in the

Massey Genome Service.

The alignments were sorted manually to determine sequences appropriate for

marker development. Regions of particular interest were those that exhibited

polymorphisms between the two frog species and between these and the Taveuni

frogs. Furthermore, loci were chosen with consideration for designing primers (i.e.

primer sequences needed to be of sufficient length to design primers of a length of

21- 26 bp, not contain sequences that would generate hairpins in amplicons, low to

no dimerization capacity, and no secondary priming sites along the template strand

between designed forward and reverse primers). Initially twelve loci were chosen

from the 33 contiguous sequence alignments based on the presence of sufficient

polymorphisms. These 12 loci were then used as DNA template sequence and trialled

on Oligo 6.0 for primer design. Eventually six primer pairs of 22- 30bp were

designed and ordered for PCR screening, based on their suitability.

The primer pairs were then trialled by PCR against frog DNAs from a range

of populations (one from each island) and PCR products were run on 1% (w/v)

agarose gels. The utility of a primer was determined if the PCR produced a single

clear band in the gel picture for all the frog DNA samples tested. Of the six primer

pairs we trialled initially, four pairs successfully amplified DNA from frogs across

all trailed populations. Further PCRs were performed on a larger dataset including

40 frogs from 29 of the 32populations separated by a geographical distance greater

than 10 km (Table 5.1). PCR products were cleaned using the Big Dye protocol and

sequenced on an ABI3730 capillary sequencer.

5.2.3 Alignments, splitsgraphs and model determination

Nuclear and mitochondrial sequences generated by PCRs described above,

were edited manually with Sequencher 4.0 and then aligned in ClustalX 1.8

89

(Thompson et al. 1997). Initial alignments were edited (trimmed, ambiguities and

gap only-columns removed) using a text editor. Of the four nuclear primer sets

initially trialled, only three produced unambiguous sequences: sequences from the

fourth primer pair trial contained many ambiguities potentially resulting from length

differences in multiple amplification products. Datasets were determined for

multiple sequences of the three nuclear markers. These were then each analysed

separately. In the case of the mitochondrial markers (12S and cytb) these were

analysed separately and in concatenation. Concatenations were made for 40

individual frog DNAs from multiple populations of ground and tree frogs. This was

done in SplitsTree 4.0 (Huson and Bryant 2006) to form a 1070 bp 12SrRNA cytb

dataset with no gaps and ambiguities.

Neighbour Net splitsgraphs were built for the six alignments (three nuclear,

12SrRNA, cytb and 12SrRNA+cytb data sets) using SplitsTree 4.0 and p-distances.

These graphs allowed the potential of the novel nuclear markers to be evaluated as

they don’t necessarily assume the sequence data have a tree-like evolutionary history

(Bryant and Moulton 2004). Nodes in the splitsgraphs were made more visible and

colour coded according to genotype or island group. To make quantitative

comparisons between ground and tree frog populations and their genetic diversity in

different locations, Phylogenetic Diversity (PD) was calculated. For this purpose the

PD calculation of Faith (1992) was used where PD is measured as “the sum of the

weights for all splits that separate… taxa into two non-empty groups”. Essentially

this measures the sum of branch lengths between all taxa (or any subset of taxa) in a

phylogenetic graph (split network or tree). Thus it provides an objective way of

comparing genetic diversity among island populations and/or between locations.

For PhyML tree building, a model of nucleotide sequence evolution was first

selected using jModelTest 2.1.4 (Darriba et al. 2011) for five loci (nuc5, nuc8 and

nuc11, 12S+cytb). The jModelTest html output describes the model of molecular

evolution (data partitioning scheme), proportion of invariable sites (p-inv), gamma of

the distribution (Γ), rate change frequencies, and base frequencies.

90

Tab

le 5

.1 F

iji fr

og sa

mpl

es u

sed

in P

CR

and

phy

loge

netic

ana

lyse

s des

crib

ed i

n te

xt.

Isla

nd

Site

Sa

mpl

e ID

Sp

ecie

s

Isla

nd

Site

Sa

mpl

e ID

Sp

ecie

s G

au

Ivita

kala

i Iv

i3

C. v

itian

us

Viti

Lev

u M

atok

ana

Mtk

10

C. v

itien

sis

Gau

N

abod

ua

Nab

1 C

. viti

anus

V

iti L

evu

Mat

okan

a M

tk2

C. v

itien

sis

Gau

N

abod

ua

Nab

2 C

. viti

anus

V

iti L

evu

Nad

ariv

atu

Ndr

17

C. v

itien

sis

Gau

N

abod

ua

Nab

3 C

. viti

anus

V

iti L

evu

Nad

ariv

atu

Ndr

3 C

. viti

ensi

s G

au

Nak

alira

u N

ak7

C. v

itian

us

Viti

Lev

u N

aga

Nga

15

C. v

itien

sis

Gau

N

avas

a N

av11

C

. viti

anus

V

iti L

evu

Nag

a N

ga3

C. v

itien

sis

Gau

N

avas

a N

av6

C. v

itian

us

Viti

Lev

u N

akau

vadr

a N

aka1

C

. viti

ensi

s G

au

Nav

asa

Nav

9 C

. viti

anus

V

iti L

evu

Nak

auva

dra

Nak

a12

C. v

itian

us

Gau

V

alei

bi

Val

5 C

. viti

anus

V

iti L

evu

Nak

auva

dra

Nak

a22

C. v

itien

sis

Ova

lau

Dak

uina

mar

a D

k14

C. v

itian

us

Viti

Lev

u N

akau

vadr

a N

aka8

C

. viti

anus

O

vala

u D

akui

nam

ara

Dk2

C

. viti

anus

V

iti L

evu

Nal

idi

Nld

2 C

. viti

ensi

s O

vala

u D

amu

D2

C. v

itian

us

Viti

Lev

u N

alid

i N

ld7

C. v

itien

sis

Ova

lau

Gus

uniw

ai

G13

C

. viti

anus

V

iti L

evu

Nav

ai

Nvi

2 C

. viti

ensi

s O

vala

u Lo

ru

L33

C. v

itian

us

Viti

Lev

u N

avai

N

vi6

C. v

itien

sis

Ova

lau

Nai

katin

i N

15

C. v

itian

us

Viti

Lev

u N

avun

ibau

N

nb2

C. v

itien

sis

Tave

uni

Lom

alag

i Lo

m15

C

. viti

anus

V

iti L

evu

Nav

unib

au

Nnb

5 C

. viti

ensi

s Ta

veun

i Q

elen

i Ck

Qel

3 C

. viti

anus

V

iti L

evu

Nuk

user

e N

uk1

C. v

itien

sis

Tave

uni

Rav

ilevu

R

av4

C. v

itian

us

Viti

Lev

u N

ukus

ere

Nuk

3 C

. viti

ensi

s Ta

veun

i So

love

So

l2

C. v

itian

us

Viti

Lev

u V

unis

ea

Vun

10

C. v

itian

us

Tave

uni

Tavo

ro

Tav9

C

. viti

anus

V

iti L

evu

Vun

isea

V

un3

C. v

itian

us

Tave

uni

Tua

Tua1

3 C

. viti

anus

V

iti L

evu

Vun

isea

V

un5

C. v

itien

sis

Van

ua L

evu

Drit

i D

ri1

C. v

itien

sis

Viti

Lev

u V

unis

ea

Vun

7 C

. viti

anus

V

anua

Lev

u D

riti

Dri5

C

. viti

ensi

s V

iti L

evu

Wai

nam

akut

u W

nk20

C

. viti

ensi

s V

anua

Lev

u N

asea

levu

N

as2

C. v

itian

us

Viti

Lev

u W

aina

mak

utu

Wnk

4 C

. viti

ensi

s V

anua

Lev

u N

auru

ru

Nau

1 C

. viti

ensi

s V

iwa

Nai

vitu

ka

Vi4

6 C

. viti

anus

V

anua

Lev

u V

euku

Sa

q2

C. v

itian

us

Viw

a N

auru

ru

Vi8

C

. viti

anus

V

anua

Lev

u W

aisa

li R

eser

ve

Sav1

2 C

. viti

ensi

s

Viw

a To

vuni

V

i30

C. v

itian

us

91

5.2.4 Maximum Likelihood (ML) analyses

Newick-formatted multiple sequence alignments were run on PhyML 3.1

(Guindon et al. 2010), using the model parameters calculated in jModelTest (model

of molecular evolution, p-inv, Γ, base change rates, and base frequencies). The best

heuristic PhyML tree topologies obtained were the result of the ‘best of nearest

neighbour interchange (NNI) and sub-branch pruning and re-grafting

(SPR)’searching. Non-parametric bootstrapping was not used in analyses of the

individual gene data sets because of the low number of character states in the data

matrices. 100 replicates were made in the case of the concatenated 12SrRNA+cytb

data set, and phylogenetic uncertainty visualised using a consensus network (Holland

et al. 2005) in SplitsTree 4.0 (Huson and Bryant 2006). Genetic distances between

populations were estimated in Splitstree as PD values rather than Fst as the sample

size precluded use of the latter statistic.

5.2.5 BEAST analyses

To infer the source location for range expansion of ground and tree frogs we

conditioned phylogenetic reconstruction of genetic variation for the 12SrRNA+cytb

data set on population locations and reconstructed ancestral locations using BEAST

2.0 (Remco et al. 2012). Using the HPD limits (59 and 23 ma) obtained in Chapter 4

as estimates for the divergence time of Fijian ground and tree frogs, sequence

divergence among frogs of both Fijian species in the concatenated 12SrRNA+cytb

data set was evaluated. The aim was to provide a tentative estimate for the timing of

separation of mitochondrial haplotypes found in different geographic locations. In

this analysis, chains were run for 50 million cycles, the root was calibrated assuming

a normal distribution (mean of 23 or 59 ma and SD of 0.1), a Yule model of

speciation and a relaxed (lognormal) clock model were assumed. The substitution

model assumed was that inferred to be optimal under jModelTest (Akaike Criterion).

20% of trees were removed as burnin using TreeAnnotator (from the Beast V1.8

package) and the major clade credibility tree was calculated and then visualised

using FigTree v1.4.1. (http://tree.bio.ed.ac.uk/software/figtree/). Additionally, in

separate analyses of ground and tree frog sequences I made an attempt to reconstruct

ancestral locations for each species (Suchard et al. 2012), phylogenetic

reconstruction was conditioned on population locations. For this analysis, a

92

coalescent model for sequence divergence, and the optimal (Akaike Criterion)

jModelTest substitution models for ground and tree frogs were assumed.

5.3 RESULTS

5.3.1 Phylogeographic structure in 12SrRNA and Cytb genes of Fijian

Ceratobatrachids

Strong phylogeographic structuring can be readily inferred from the

Neighbour Net splitsgraphs for 12S and cytb as well as their concatenated dataset

(Figures 5.1-5.3). The tree-like Neighbour Nets for individual loci indicate relatively

few incompatibilities in the data matrices. Whilst the sample size was small, the

colouring of nodes nevertheless indicates strong partitioning of haplotypes into

source locations. The Taveuni ground frogs cluster together, as do the Viwa Island,

and Vanua Levu Island populations for both species.

A large clade of frogs from populations comprising three geographically

close islands (minimum distances: Viti Levu-Gau =57 km, Gau-Ovalau =51 km,

Ovalau-Viti Levu = 16 km) exist with very little genetic divergence (or phylogenetic

diversity – see below) among these frog populations. The Viwa population stands

out as being more genetically distinct but this population is nevertheless closely

related to other members of this clade. Viwa Island is a small 0.6 ha island 990 m

from the eastern coastline of Viti Levu.

The genetic distance between C. vitianus and C. vitiensis is large and this is

evident from the Neighbour Nets as well as the ML trees. Cornufer vitiensis

populations appear to have highly diverged populations of frogs on both Vanua Levu

and Viti Levu (see Figures 5.1b, 5.2b, and 5.3b and also measures of PD reported

below). In contrast there is low genetic divergence among the island populations

where C. vitianus is found. A striking observation is the extent of genetic divergence

between Viti Levu, Taveuni and Vanua Levu populations of ground frog. The

Taveuni populations appear more closely related to the Vanua Levu populations than

they do to the Viti Levu populations.

The consensus network (0.33 threshold level for splits used) of the 100

bootstrap trees from the concatenated 12SrRNA+cytb dataset (Figure 5.3c) shows the

same tree topology as the optimal PhyML tree. Overall, the splitsgraphs and ML

trees concur on the placement of branches, with low bootstrap support for certain

branches in the concatenated 12SrRNA+cytb ML tree occurring at the same nodes

93

where the Neighbour Net shows contradictory splits (Figures 5.3a and 5.3b). These

incompatibilities occur in the upper part of Figure 5.3a and concern the relationships

between Wnk4, Nau1, and the large clade of Ovalau+Gau+Viti Levu (C. vitianus), as

well as between Nas2, Saq2 and Dri1. It is perhaps noteworthy that the most

incompatible splits concern Vanua Levu C. vitianus and C. vitiensis frogs.

5.3.2 Phylogeographic structure of novel nuclear markers in Fijian

Ceratobatrachids

ML trees and Neighbour Net splitsgraphs built from analysis of the nuclear

single nucleotide polymorphisms (SNPs) in the novel nuclear markers show less

pronounced geographic structuring compared to the mitochondrial gene trees, as

perhaps might be expected given the different effective population size of nuclear

and mitochondrial genomes. Figures 5.4a and b nuclear locus (nuc5) contain splits

compatible with the mitochondrial gene trees but also notable differences.

Phylogenetic analysis of nuc5 indicates relatively low genetic variation among C.

vitianus individuals with most of the island populations forming one clade. The

Taveuni population of ground frogs is not as genetically distinct from other ground

frog populations as suggested by the mitochondrial markers. In contrast with the

ground frogs, but similar to the findings with mitochondrial markers, in nuc5, there is

relatively high genetic diversity among C. vitiensis populations in the Fijian Islands.

This conclusion can be drawn from both the Neighbour Net and PhyML tree.

One notable observation is the grouping of tree frog haplotypes with ground frogs.

This might be explained by incomplete lineage sorting, introgression or even

evolutionary properties of the markers if PCR amplification has not been selective

for orthologues. The alignment of sequences amplified for nuc8 indicates a very

large evolutionary distance between ground and tree frogs. For this reason

phylogenetic graphs are shown separately for both species. The graphs for this

marker indicate some phylogeographic patterns. For example the graph for nuc8_1

locus, comprises mostly C. vitianus. At this locus, ground frogs from Viti Levu and

adjacent lands are genetically similar and distinct from those from Taveuni.

94

Fi

gure

5.1

a N

eigh

bour

Net

split

sgra

ph fo

r a c

onse

rvat

ive

12Sr

RN

A a

lignm

ent o

f 40

frog

s fro

m 2

9 po

pula

tions

on

six

isla

nds i

n th

e Fi

ji ar

chip

elag

o

(am

bigu

ities

and

inde

ls re

mov

ed).

Circ

les a

re C

. viti

ensi

s and

squa

res a

re C

. viti

anus

. O

rang

e no

des a

re fo

r Viti

Lev

u sa

mpl

es, f

usch

ia n

odes

are

for

the

Ova

lau+

Gau

+Viw

a+V

iti L

evu

clad

e, g

reen

nod

es a

re fo

r Van

ua L

evu

sam

ples

, and

blu

e no

des a

re fo

r Tav

euni

sam

ples

.

95

Fi

gure

5.1

b O

ptim

al m

axim

um li

kelih

ood

(ML)

tree

for a

con

serv

ativ

e12S

rRN

A a

lignm

ent o

f 40

frog

s fro

m 2

9 po

pula

tions

on

six

isla

nds i

n th

e Fi

ji

arch

ipel

ago

(am

bigu

ities

and

inde

ls re

mov

ed).

Nod

e co

lour

and

shap

e sc

hem

e fo

llow

s Fig

ure

5.1a

.

96

Fi

gure

5.2

a N

eigh

bour

Net

split

sgra

ph fo

r a c

onse

rvat

ive

cyto

chro

me

oxid

ase

b (c

ytb)

alig

nmen

t of 4

0 fr

ogs f

rom

29

popu

latio

ns o

n si

x is

land

s in

the

Fiji

arch

ipel

ago

(no

ambi

guiti

es o

r ind

els)

. C

ircle

s are

C. v

itien

sis a

nd sq

uare

s are

C. v

itian

us.

Ora

nge

node

s are

for V

iti L

evu

sam

ples

, fus

chia

nod

es a

re

for t

he O

vala

u+G

au+V

iwa+

Viti

Lev

u cl

ade,

gre

en n

odes

are

for V

anua

Lev

u sa

mpl

es, a

nd b

lue

node

s are

for T

aveu

ni sa

mpl

es.

Whi

te c

ircle

s or

squa

res r

epre

sent

mix

ed c

lade

s nod

es.

97

Fi

gure

5.2

b O

ptim

al m

axim

um li

kelih

ood

(ML)

tree

for a

con

serv

ativ

e cy

toch

rom

e ox

idas

e b

(cyt

b) a

lignm

ent o

f 40

frog

s fro

m 2

9 po

pula

tions

on

six

isla

nds

in th

e Fi

ji ar

chip

elag

o (n

o am

bigu

ities

or i

ndel

s). N

ode

colo

ur a

nd sh

ape

sche

me

follo

ws F

igur

e 5.

2a.

98

Fi

gure

5.3

a N

eigh

bour

Net

split

sgra

ph fo

r con

cate

nate

d cy

toch

rom

e ox

idas

e b

(cyt

b) a

nd 1

2SrR

NA

alig

nmen

t of 4

0 fr

ogs f

rom

29

popu

latio

ns o

n si

x is

land

s

in th

e Fi

ji ar

chip

elag

o. C

ircle

s are

C. v

itien

sis a

nd sq

uare

s are

C. v

itian

us.

Ora

nge

node

s are

for V

iti L

evu

sam

ples

, fus

chia

nod

es a

re fo

r the

Ova

lau+

Gau

+Viw

a+V

iti L

evu

clad

e, g

reen

nod

es a

re fo

r Van

ua L

evu

sam

ples

, and

blu

e no

des a

re fo

r Tav

euni

sam

ples

. W

hite

circ

les r

epre

sent

mix

ed c

lade

nod

es.

99

Fi

gure

5.3

b O

ptim

al m

axim

um li

kelih

ood

(ML)

tree

with

boo

tstra

p su

ppor

t for

con

cate

nate

d cy

toch

rom

e ox

idas

e b

(cyt

b) a

nd 1

2SrR

NA

alig

nmen

t of 4

0

frog

s fro

m 2

9 po

pula

tions

on

six

isla

nds i

n th

e Fi

ji ar

chip

elag

o. N

ode

colo

ur a

nd sh

ape

sche

me

sam

e as

for F

igur

e 5.

3a.

100

Fi

gure

5.3

c C

onse

nsus

net

wor

k sp

litsg

raph

of 1

00 b

oots

trap

max

imum

like

lihoo

d tre

es fo

r con

cate

nate

d cy

toch

rom

e ox

idas

e b

(cyt

b) a

nd 1

2SrR

NA

alig

nmen

t of 4

0 fr

ogs f

rom

29

popu

latio

ns o

n si

x is

land

s in

the

Fiji

arch

ipel

ago.

Nod

e co

lour

and

shap

e sc

hem

e sa

me

as fo

r Fig

ure

5.3a

.

101

Two Vanua Levu tree frogs are also represented at this locus (Nau1 and

Dri5). They are most similar to a ground frog also from Vanua Levu (Nas2). At the

second locus amplified by the same primer pair for nuc8, all sequences are of C.

vitiensis. Here the genetic diversity of the Vanua Levu populations is clustered and

less than the total genetic variation represented by the Viti Levu tree frogs.

Phylogenetic analysis of nuc11 sequences also produced two distinct

alignment blocks. One of these comprised mostly C. vitianus (shown as nuc11_1 in

Figures 4.6a and 4.6b)), and the other comprised only C. vitiensis frogs (shown as

nuc11_2 in Figures 4.6c and 4.6d)). In the Neighbour Net splitsgraph (Figure 4.6a),

the C. vitianus populations cluster together, with a longer branch leading to two tree

frog species. Again interestingly, these are Vanua Levu tree frogs. Nas2 and Saq2

are tree frogs from geographically separate (>53 km over the central mountain

ranges) locations on Vanua Levu, where sympatric populations of C. vitianus and C.

vitiensis occur. The geographic and infra-specific splits (observations described

above) are clearer in the ML tree (Figure 4.6c) than in the Neighbour Nets.

Figure 4.6c provides a visualization that indicates the relatively high genetic

diversity (when compared against C. vitianus) of C. vitiensis on both Vanua Levu

and Viti Levu seen in the other markers (nuclear and mitochondrial). Frogs from the

Namosi region (Nuk1, Nuk3, and Mtk2) are quite divergent from the other central

Viti Levu populations. It is possible these are ancestral genotypes from which other

genotypes might have been derived.

5.3.3 Phylogenetic Diversity (PD)

Table 5.2a-b shows comparisons of PD that formally summarises and

quantifies inferences indicated by the Neighbour Nets and PhyML trees for

mitochondrial and nuclear markers. Observations include: a) tree frogs show high PD

in Viti Levu and Vanua Levu; b) ground frogs show low PD in Viti Levu and higher

PD in Vanua Levu c) PD is low within and between ground frog populations of Viti

Levu and adjacent islands but d) high between Taveuni, Vanua Levu and Viti Levu;

e) only some nuclear markers corroborated a high PD between Taveuni and Viti

Levu populations.

Two sets of PD estimates were derived, one set calculating the PD diversity

based on the marker, and the other comparing the phylogenetic diversity between the

C. vitianus and C. vitiensis populations as well as the infra-specific PD estimates

102

(Table 5.2a). Based on the PD values, cytb was the marker that encapsulated the

most phylogenetic diversity of the Fijian Ceratobatrachids, at 91.4%, followed by

12SrRNA at 50.4%, and then the concatenated 12S+cytb dataset at 20.9%. Average

PD value for the three nuclear markers was low at 5.1%. This is to be expected

given that this is an infra-specific phylogenetic comparison and given the larger

effective population size, and generally slower evolving rates of nuclear genomes.

The high genetic diversity present within the nuclear and mitochondrial

genomes of the Fiji tree frog (C. vitiensis) suggested by the tree topologies is verified

by the PD estimates. C. vitiensis contributes more than 50% of the total phylogenetic

diversity for the concatenated mitochondrial sequences, 12SrRNA, nuc5, nuc8_2 and

nuc11_2 (Table 5.2b). On average, PD for the C. vitiensis samples is about 57.4%

(nuclear and mitochondrial markers in this study).

In contrast C. vitianus only contributes 24.4% on average for the same loci.

PD for C. vitianus populations was higher (in terms of contribution of the clade to

the overall PD calculated for the marker) for the nuclear markers than for the

mitochondrial markers. In the most often sequenced mitochondrial marker, cytb, PD

values were similar for both species (26.4% for C. vitianus and 28.1% for C.

vitiensis). Phylogenetic diversity within the Taveuni clade is very low (<2.0% for all

markers except nuc11_1), indicating little divergence between these populations.

The furthest geographical distance between the Taveuni populations is approximately

26.5km, between Tavoro to the north and Ravilevu Reserve in the south. In two

markers, cytb and nuc8_1, the level of PD is negligible suggesting that at those

mitochondrial and nuclear loci, there has been little divergence since C. vitianus

frogs colonized the volcanic island.

103

Fi

gure

5.4

a N

eigh

bour

Net

split

sgra

ph fo

r nuc

lear

SN

P al

ignm

ent (

nuc5

) of 4

0 fr

ogs f

rom

29

popu

latio

ns o

n si

x is

land

s in

the

Fiji

arch

ipel

ago.

Circ

les a

re C

.

vitie

nsis

and

squa

res a

re C

. viti

anus

. O

rang

e no

des a

re fo

r Viti

Lev

u sa

mpl

es, f

usch

ia n

odes

are

for t

he O

vala

u+G

au+V

iwa+

Viti

Lev

u cl

ade,

gre

en

node

s are

for V

anua

Lev

u sa

mpl

es, a

nd b

lue

node

s are

for T

aveu

ni sa

mpl

es.

Whi

te c

ircle

s and

squa

res r

epre

sent

iden

tical

gen

otyp

es in

frog

s fro

m

diff

eren

t loc

atio

ns.

104

Figu

re 5

.4b

Opt

imal

max

imum

like

lihoo

d (M

L) tr

ee fo

r nuc

lear

SN

P al

ignm

ent (

nuc5

) of 4

0 fr

ogs f

rom

29

popu

latio

ns o

n si

x is

land

s in

the

Fiji

arch

ipel

ago.

Nod

e co

lour

and

shap

e sc

hem

e sa

me

as fo

r Fig

ure

5.3a

.

105

Figure 5.5a Neighbour Net splitsgraphs for nuclear SNP alignment (nuc8_1 and

nuc8_2) of 40 frogs from 29 populations on six islands in the Fiji

archipelago. Circles are C. vitiensis and squares are C. vitianus. Orange

nodes are for Viti Levu samples, fuschia nodes are for the

Ovalau+Gau+Viwa+Viti Levu clade, green nodes are for Vanua Levu

samples, and blue nodes are for Taveuni samples. White circles represent

identical genotypes in frogs from different localities.

106

Figure 5.5b Optimal maximum likelihood (ML) tree for nuclear SNP alignment (nuc8_1

and nuc8_2) of 40 frogs from 29 populations on six islands in the Fiji archipelago.

Node colour and shape scheme same as for Figure 4.5a.

107

Fi

gure

5.6

a N

eigh

bour

Net

split

sgra

ph fo

r nuc

lear

SN

P al

ignm

ent (

nuc1

1_1)

of 4

0 fr

ogs f

rom

29

popu

latio

ns o

n si

x is

land

s in

the

Fiji

arch

ipel

ago.

Circ

les a

re C

. viti

ensis

and

squa

res a

re C

. viti

anus

. O

rang

e no

des a

re fo

r Viti

Lev

u sa

mpl

es, f

usch

ia n

odes

are

for t

he

Ova

lau+

Gau

+Viw

a+V

iti L

evu

clad

e, g

reen

nod

es a

re fo

r Van

ua L

evu

sam

ples

, and

blu

e no

des a

re fo

r Tav

euni

sam

ples

. W

hite

circ

les

repr

esen

t ide

ntic

al g

enot

ypes

from

diff

eren

t loc

aliti

es.

108

Fi

gure

5.6

b N

eigh

bour

Net

split

sgra

ph fo

r nuc

lear

SN

P al

ignm

ent (

nuc1

1_2)

of 4

0 fr

ogs f

rom

29

popu

latio

ns o

n si

x is

land

s in

the

Fiji

arch

ipel

ago.

Nod

e co

lour

and

shap

e sc

hem

e sa

me

as fo

r Fig

ure

4.6a

.

109

Fi

gure

5.6

c O

ptim

al m

axim

um li

kelih

ood

(ML)

tree

for n

ucle

ar S

NP

alig

nmen

t (nu

c11_

1) o

f 40

frog

s fro

m 2

9 po

pula

tions

on

six

isla

nds i

n th

e Fi

ji

arch

ipel

ago.

Nod

e co

lour

and

shap

e sc

hem

e sa

me

as fo

r Fig

ure

4.6a

.

110

Fi

gure

5.6

d O

ptim

al m

axim

um li

kelih

ood

(ML)

tree

for n

ucle

ar S

NP

alig

nmen

t (nu

c11_

2) o

f 40

frog

s fro

m 2

9 po

pula

tions

on

six

isla

nds i

n th

e Fi

ji

arch

ipel

ago.

Nod

e co

lour

and

shap

e sc

hem

e sa

me

as fo

r Fig

ure

4.6a

.

111

5.3.4 BEAST statistical analyses

Using the HPD limits of 59 and 23 ma for the divergence time of Fijian Frogs

obtained with BEAST v1.8 in Chapter 4, further estimates were made with BEAST

v2.0 for the divergence times of tree frog and ground frog 12SrRNA + cytb

mitochondrial genotypes (Fig 5.7a, 5.7b, and 5.7c). Independently, estimates were

additionally made using BEAST v2.0 to test the location of ancestral populations.

Analyses of the ground frog data indicate that Vanua Levu has greatest probability of

being the ancestral location for C. vitianus (Table 5.3). However, this estimate is

based on limited sampling from Vanua Levu and must be treated with cautionary

discretion. With respect to estimation of the ancestral locations for C. vitiensis, the

Bayesian analyses were unable to discriminate between Vanua Levu and Viti Levu

for root placement, and all the runs terminated before completion of all cycles. This

lack of resolution might be expected given the level of genetic divergence of C.

vitiensis on Viti Levu and Vanua Levu, as indicated in the PhyML trees and

Neighbour Net splitsgraphs.

The chronogram for population divergence made assuming the lower HPD

limit of 23 ma (from Chapter 4) suggests divergence of C. vitianus (Taveuni)

populations from Vanua Levu frog populations by 10.6 ma. In runs constrained by

the upper HPD of 59 ma, the estimated time for divergence was 30.3 ma. Therefore

the time range for divergence of the Taveuni populations from a putative source

population from nearby large island Vanua Levu is suggested to be between 10 - 30

ma.

5.4 DISCUSSION

5.4.1 Cornufer vitianus (Taveuni)

Taveuni frogs stand out as a genetically distinct and ecologically unusual sub-

species of C. vitianus. They behave similarly to tree frogs and are arboreal in nature.

They also are polymorphic in terms of dorsal colouration and melanistic patterning.

The level of genetic divergence in mitochondrial markers between the Taveuni

population and other ground frogs is noticeable in Chapter 4, where it is clear that the

two taxa are not the same species based on the branch lengths of the mt protein

coding genes and RNA trees.

112

Table 5.2a Phylogenetic Diversity (PD) estimates from neighbour network

splitsgraphs and optimal ML trees of two mitochondrial and three nuclear

markers. Dataset Phylogenetic Diversity (PD) Average Distance Concatenated cytb+12S 0.4076433 0.1092645 Optimal Phyml tree 0.2091281 12SrRNA 0.3687813 0.0930134 Optimal Phyml tree 0.5399730 cytb 0.4552899 0.1403115 Optimal Phyml tree 0.9141160 nuc5 0.0694649 0.0179379 Optimal Phyml tree 0.0891471 nuc8_1 0.0416228 0.0132046 Optimal Phyml tree 0.0431092 nuc8_2 0.0556995 0.0128542 Optimal Phyml tree 0.0717800 nuc11_1 0.0253171 0.0088045 Optimal Phyml tree 0.0280923 nuc11_2 0.0415689 0.0112995 Optimal Phyml tree 0.0457418

113

Tab

le 5

.2b

Phyl

ogen

etic

Div

ersi

ty (P

D) e

stim

ates

from

opt

imal

ML

trees

of C

. viti

anus

and

C. v

itien

sis i

slan

d po

pula

tions

.

Dat

aset

C

ornu

fer v

itian

us

C

ornu

fer v

itien

sis

Va

nua

Levu

Ta

veun

i O

ther

s

Van

ua L

evu

Cen

tral V

iti L

evu

Nor

ther

n V

iti L

evu

East

ern

Viti

Lev

u C

onca

tena

ted

cytb

+12S

0.

0476

24

0.00

7988

0 0.

0070

49

0.15

6669

0.

195

0.00

9031

001

0.00

7095

6.

5%

1.0%

0.

9%

21.4

%

26.7

%

1.2%

0.

9%

12Sr

RN

A

0.04

0065

0 0.

0101

560

0.01

0184

0.

1157

59

0.07

5366

996

0.01

0137

999

0.00

2883

7.

2%

1.8%

1.

8%

20.9

%

13.6

%

1.8%

0.

5%

cytb

0.

0729

010

0.00

2557

0 0.

0078

280

0.21

0923

0 0.

7594

13

0.01

5808

0.

0076

57

7.9%

0.

2%

0.8%

13

.0%

83

.0%

1.

6%

0.8%

nu

c5

0.00

6270

1 N

/A

0.00

0000

57

0.01

2595

9 5.

1351

752

0.01

2565

3 0.

0032

5978

7.

0%

0.

0%

14.1

%

57.6

%

14.0

%

3.6%

nu

c8_1

0.

0000

005

0.00

0000

3 0.

0143

7347

1 0.

0047

715

N/A

N

/A

N/A

0.

0%

0.0%

33

.3%

11

.0%

nu

c8_2

N

/A

N/A

0.

0238

7300

1 0.

0164

48

0.00

6715

0.

0112

59

N/A

33

.2%

22

.9%

9.

3%

15.6

%

nuc1

1_1

0.00

4007

0 0.

0039

970

0.00

3975

0.

0040

11

N/A

N

/A

N/A

14

.2%

14

.2%

14

.1%

14

.2%

nu

c11_

2 N

/A

N/A

N

/A

0.00

3059

2 0.

0305

6647

0.

0060

4604

9 0.

0030

238

6.6%

66

.8%

13

.2%

6.

6%

114

Table 5.3 Ancestral Location Probabilities for C. vitianus and C. vitiensis Island

Populations from BEAST 2.0.

Island Population C. vitianus Probability as Ancestral Location for Other Populations Vanua Levu 0.238470191

Viti Levu 0.136607924

Taveuni 0.216097988 Gau 0.126484189

Ovalau 0.13535808

Viwa 0.146981627

C. vitianus Vanua Levu 0.485491861 Viti Levu 0.514508139

115

Figure 5.7a BEAST chronogram for C. vitianus and C. vitiensis populations dated on HPD

lower probability estimate of 23 ma.

116

Figure 5.7b BEAST chronogram for C. vitianus and C. vitiensis populations dated on HPD

lower probability estimate of 59 ma.

117

Cryptic divergence in closely related lineages of frogs has been inferred for

other frog species (Stuart et al. 2006; Tolley et al. 2010; Prado et al. 2012). Whether

the Taveuni population is a cryptic lineage of ground frogs, remains to be further

tested in analyses with additional independent nuclear loci. The short genetic

distances seen on the Neighbour Nets and ML trees between the Taveuni frogs and

Vanua Levu tree frogs suggest ancestral genetic connectivity, which would be

plausible given the hypothesis of a putative land bridge during glacial maxima

(Duffels and Turner 2002). There exists a high degree of morphological variation

between Taveuni C. vitianus and other island populations of C. vitianus. Although

the geological age of Taveuni Island is still unconfirmed, dating of volcanic rocks on

the islands suggest a history of island-building volcanism in the last two million

years (Neall and Trewick 2008).

The long branch lengths between the Vanua Levu Island populations in all

the ML trees and Neighbour Net splitsgraphs can be interpreted in several ways.

Sufficient time and isolation of the Vanua Levu species within relict forest patches

has led to substantial genetic divergence between C. vitiensis and C. vitianus

populations. As suggested from the BEAST analysis, ancestral genetic diversity

(evolved in the Fijian Ceratobatrachids hypothetical source area) has remained extant

on the larger islands since the two species evolved in a putative source area within

the Vitiaz arc. On the smaller islands, genetic drift and/or natural selection have

driven the fixing of haplotypes and populations have become less genetically diverse

since colonisation of these small islands.

Conversely, the short branch lengths between other ground frog populations

(the large Ovalau + Gau + Viti Levu clade), and also within these lineages, suggests

a rapid expansion from a source area (likely Vanua Levu as the large size of this

island would have offered greater opportunity for refugia) out into the current

distribution/ range (Figure 4.6d). The putative divergence time estimates for the

divergences of the island populations within this large clade (<10.5 ma) falls within

the late Pleistocene and succeeding Holocene, and may be associated with warmer

temperatures and forest expansion out of glacial montane refugia. Rapid post-

Pleistocene expanse of ectotherms like anurans has been demonstrated before in the

southern tropics for other taxa (Wang et al. 2014). In the Wang study, decreased

genetic diversity and population scale differentiation between island populations is

attributed to isolation by rising sea surfaces during the Holocene succeeded by

118

random genetic drift. Rapid population expansion during the late Pleistocene or

early Holocene, leading to reduced genetic diversity in populations of Atlantic forest

birds was suggested by Cabanne et al. (2008).

5.4.2 Hybridisation between Fijian frogs?

Subtle clues in the nuclear data suggest historical introgression between C.

vitianus and C. vitiensis. This includes the sharing of similar genotypes in both

species in Vanua Levu frog populations (e.g. Figure 5.5a, c; 5.6a, c). However, this

hypothesis needs to be tested with additional molecular markers and frog samples

(e.g. as per Joly 2012). The inferred divergence times between ground frogs and tree

frogs might suggest these species are likely to be reproductively isolated; however

the temporal estimate of their divergence time (Chapter 4) is tentative and needs to

be further tested. Other hints at hybridisation are the behavioural differences between

Taveuni and other ground frog populations.

Tree climbing is generally a tree frog’s way of life, however, this behavioural

prevalence in Taveuni ground frog populations may be linked to the smaller size of

individuals in the island population. The toe discs of Taveuni frogs are similar in

size to the Ground frog and have not evolved into larger toe discs as most tree

dwelling species such as C. vitiensis have. An additional clue may be the highly

polymorphic colouration and patterning of Fijian Ceratobatrachid skin. Recent

research with other anuran species that have similar levels of colour polymorphism

has suggested that hybridisation between closely related taxa, has driven colour

polymorphism (Brown et al. 2010; O’Neill and Beard 2010).

Colour polymorphism is an adaptive trait and is linked to spectrally variable

microhabitats to reduce the probability of predators developing a search image

(Lowe and Hero 2012). Melanistic patterning (lines, blotches, spots, etc.) that break

up the lines of a frog’s body, and colours that match the microhabitat selected by the

species are effective tools in a frog’s arsenal for predator evasion (ibid.). Colour

polymorphisms in frog taxa for which selective pressure would hypothetically

constrain or stabilize expression at these genetic loci, is thought to have been

generated by transgressive phenotypic expression; i.e. when the resulting phenotype

in hybrids is novel, unlike any form presently found in the phenotypes expressed by

either parental species (Medina et al. 2013).

119

If hybridisation has occurred, possible opportunities for hybridisation would

include range changes due to vegetation shifts during glacial periods (Abbot et al.

2013) and reduction in suitable habitat due to changes in vegetation structure (which

affects the microclimate of diurnal refugia). The lack of suitable microhabitats and

macrohabitats would drive anuran populations to extirpation in much of their range

(Ryan et al. 2008; Daskin et al. 2011). Population crashes and dwindling

populations would lower the mate choice options and two biologically similar

species may be likely to hybridise.

Homoplaseous characters and the retention of ancestral polymorphisms could

be equally valid reasons for the observed phenotypic characters and shared genotypes

among the Fijian frogs (Funk 1985). Distinguishing between these possibilities is

made difficult because close phylogenetic relatives of Fijian frogs’ have not been

investigated. Furthermore, DNA of the extinct putative close relative (the Fijian

megaboto) has not survived the limestone cave conditions in which the fossils were

found. If it had, distinguishing alternative hypotheses of retention of ancestral

character states from introgressive hybridization (Mallet 2005; Streicher et al. 2014)

would be more straightforward (Joly 2012).

Given the divergence time estimates of 82-91 ma between C. vitiensis and C.

vitianus, retention of ancestral character states seems may not be the most plausible

explanation for the presence of identifical and similar shared genotypes in the

nuclear ‘species’ trees. Likewise, the argument that similiarity of genotypes in

sympatric C. vitianus and C. vitiensis populations on Vanua Levu is due to

convergent sequence evolution in the nuclear sequence data (Funk 1985), is similarly

flawed. This is suggested by the genotypes present in the mitochondrial and nuclear

gene trees, which have a clearly phylogeographically structured distribution, as

shown elsewhere (Milner et al. 2012).

In general, the retention or persistence of ancestral polymorphisms from

polymorphic ancestral species has been difficult to infer. However, it is proving

much easier now with next generation sequencing and genomic dataset analyses

(Joly 2012; Segatto et al. 2014). If incomplete lineage sorting post-speciation (which

can result in the persistence of shared polymorphisms in the nuclear genome) is the

explanation for shared genotypes between the two Fiji frog species on Vanua Levu,

then we might expect contradictory phylogenetic signals from nuclear and

mitochondrial gene trees (Knowles and Maddison 2006; Joly et al. 2009). That is

120

not what we find with the Fiji frog nuclear trees, where there is concordance between

the nuclear data sets for other island populations save for the Vanua Levu frogs.

Like the case for homoplasy, the strong geographical structuring of the other island

populations in the species trees would suggest otherwise.

Given the possibility of hybridisation having occurred in Fijian

Ceratobatrachid prehistory for whatever reason, whether recent as suggested by the

nuclear data or ancient (which was not clearly discerned in our gene trees) it will be

of interest to further examine the phenomenon in Fijian Ceratobatrachids. We need

to understand the history of this possible evolution event to determine whether

reoccurrence of hybridisation between C. vitiensis and C. vitianus may be a ‘threat’

to persistence given climate change predictions (as suggested by Muhlfeld et al.

2014), or whether hybridisation will enhance the adaptive potential of these range-

restricted species to changing climate (Becker et al. 2013). It would therefore be of

value to determine whether hybridisation is truly occurring between Fiji’s two

Ceratobatrachid species, at what level of introgression, and whether the fitness of the

parental species and hybrid offspring has been enhanced or decreased.

121

CHAPTER SIX

IMPLICATIONS FOR CONSERVATION OF THE FIJIAN FROGS

122

6.1 INTRODUCTION: HOW SPECIAL ARE THE FIJI FROGS

Fiji’s frogs are remarkable in many ways. Cornufer vitianus and C. vitiensis

represent the easternmost extent of any native amphibian species in the South Pacific

islands. These are the only anurans endemic to the Fijian archipelago. Science may

never fully elucidate the evolutionary history of these appealing animals but at least

it is now known that a unique evolutionary history must have unfolded to result in

the extant distribution of these species, their diversification and unusual pattern of

molecular evolution in their mitochondrial DNAs.

These cryptic characteristics along with traits that identify them with other

Ceratobatrachid frogs (polymorphic colouration, terrestrial breeding, calling

patterns), make for a particularly interesting branch of the anuran tree of life. It

would be a shame if this branch were to be accidentally pruned through uninformed

decision-making and policy before Fijian Ceratobatrachids were truly appreciated by

science. Logically a holistic approach is the most effective mechanism and would

therefore entail the utility of all the available scientific tools and information, to

ensure that Fiji’s Ceratobatrachids do not join the growing list of extinct amphibians.

However, there will be a challenge applying the outcomes of the geospatial and

genetics analyses described in this thesis. The situation, as elsewhere is complicated

by competing land interests, national funding limitations and available in-country

technical capacity.

6.2 HOW BEST TO APPLY THE OUTCOMES OF THE GIS ANALYSES?

6.2.1 Species Distribution Models

Species Distribution Models (SDMs) are not without their limitations.

Programming and outputs are subject to strict assumptions and are often heavily

reliant on parameter estimation. Some of the more basic concerns that have been

raised about SDMs are biological in nature: changing interspecific relationships with

climatic change; the dynamic nature of niche space; the adaptive ability of certain

taxa; species mobility including migration capacity and tendencies; and human land

modification.

Other issues described speak more to the methods applied in generating

SDMs: sampling biased datasets causing spatial autocorrelation; the level of

influence that environmental variables exert over species distributions, when

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considered separately (‘cause and effect’ assumptions); the accuracy and resolution

of variable layers and how these scales match with the species layers (Sinclair et al.

2010; Naimi et al. 2014). Despite these concerns, SDMs are additional tools to wield

when advocating for conservation change (Guisan et al. 2013). To be most effective,

conservation biologists must exercise caution when interpreting modelling results.

Nonetheless, the value of SDMs is that they can provide visually-expressed statistical

support for calls to action, particularly when inferences drawn from analyses of GIS

layers are investigated further using independent data such as genetic sequences

(Chan et al. 2011).

The main result described in Chapter Three is that ensemble SDMs developed

for both Ceratobatrachids predict distributions of 8,566.4 km2 for C. vitianus and

5,932.5 km2 for C. vitiensis. For C. vitiensis, that would fall well below the 20,000

km2 “probable extent of occurrence” for the IUCN Red List ‘Vulnerable’ category.

The estimated range area in the C. vitiensis SDM is noticeably close to the IUCN

‘Endangered’ category’s 5,000 km2 “probable extent of occurrence”. For C. vitiensis

the SDM result could be used to reassess the species’ current IUCN Red List

classification of ‘Near Threatened’.

Information gathered from field work and from the results of Chapters 3-5,

suggests modification to C. vitiensis’ Red List status:

1. Habitats – C. vitiensis distribution linked to lowland-highland tropical

rainforest (Osborne, T. et al. 2013).

2. Threats – Primary threat is habitat loss as the species is not a habitat

generalist (Sih et al. 2000); Secondary threats would be competition with

introduced Cane toad (Bufo marinus) and predation by introduced predators

(Felix catus, Rattus rattus, Rattus norvegicus, and Herpestes javanicus).

3. Stresses – Loss of rainforest habitat would lead to migration into marginal

habitat, which may not provide suitable microhabitats such as Pandanus plants.

4. Conservation Actions In Place – None actively being implemented save for

protection within forest reserves and protected areas within the Fiji protected

area network.

5. Conservation Actions Needed – Expansion of protected area network to

include sites where populations with high genetic diversity exist (Serua-Namosi,

Viti Levu; any forested area of Vanua Levu, particularly Driti and Natewa/

Tunuloa).

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6. Research Needed – Further phylogeographic analyses incorporating statistical

phylogeographic approaches and GIS data such as ‘risk’ assessments (layers

that quantify hazards according to categorical or numeric data).

7. Use and Trade – Historic uses include human harvesting for food which is a

possible cause for the extinction of congener Cornufer megabotovitiensis

(Worthy 2001).

8. Ecosystem Services – Control of flying insect populations particularly in

riparian strips thereby maintaining the balance in invertebrate food webs in Fiji

forests; possibly aids in cross-pollination as these frogs are often found adjacent

to the flowers of riparian plants (where the probability of catching insects would

be greater).

9. Livelihoods – Not applicable as frogs are no longer eaten by modern Fijian

Islanders.

6.2.2 Habitat management

The association between forested habitat and Fijian frog distribution and

abundance inferred from the SDMs, was suggested in previous research (Osborne et

al. 2008). Considering that link, the preferable management option would be to set

aside as much of the remaining forested areas in the less accessible areas identified in

SDMs (i.e. northern, western and central Viti Levu, central Vanua Levu and as much

of the forested Natewa/ Tunuloa peninsula, Taveuni, Gau, Koro, Viwa and Ovalau).

This umbrella approach would ensure that habitat size, buffer effects, and population

connectivity would be sufficiently accounted for, but is much more difficult to lobby

for and in reality only several of the protected areas suggested would be of

manageable status. Recent government interest in Vanua Levu’s forested areas may

result in the establishment of several protected areas in parts of the island that have

been demarcated for conservation (such as the Natewa/ Tunuloa peninsula). The

proposed protected area network on Vanua Levu is timely given the cryptic genetic

diversity of both ground and tree frogs in Vanua Levu (Chapter 5).

The Waisali Reserve is an existing small (1.21 km2) community-managed

(with the assistance of the National Trust of Fiji) protected area (PA) in central

Vanua Levu (NTF 2014). Expanding the borders of the reserve and seeking support

from landowners in nearby villages would be cost-effective given the size of Vanua

Levu, rather than establishing new reserves. On Viti Levu, a similar management

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option would be to expand the PA network that exists by conserving forest strips

between the major forest reserves of Pas. ‘Habitat corridors’ could be conserved

between the Sovi Basin PA (managed by Conservation International, CI), Tomaniivi-

Nadarivatu Forestry Reserve (managed by the Department of Forestry, DoF),

Savura-Vago-Coloisuva Forest Reserves (managed by DoF). At present none of the

existing parks and reserves within Fiji’s protected area system have a management

plan (the plan for the Sovi Basin is currently being drafted). To increase the

effectiveness of the proposed network of PAs on Vanua Levu and Viti Levu, the

relevant stakeholders (including the landowners) will first need to conduct a ‘gap

analysis’ to identify the existing issues for management of the reserves.

Recommendations from this gap analysis could then be incorporated into

management plans for the current PAs. New protected areas to propose based on the

outcomes of the geospatial analyses would be the remnant forests on Gau Island,

Ovalau (Lovoni Valley), Koro, and Taveuni Island. New protected areas to propose

based on the outcomes of the genetic analyses (as indicated by the PD analyses)

would be:

i. The Namosi province and Nakauvadra forests on Viti Levu where

distinct genotypes of Cornufer vitiensis are found.

ii. Any of the sites on Vanua Levu where distinct genotypes of both

species are found.

iii. Habitats that will preserve the genetic diversity inferred between

island populations (Taveuni, Viti Levu and Vanua Levu).

6.3 CAN INFERENCES OF POPULATION HISTORY INFORM

CONSERVATION EFFORTS?

6.3.1 Clues from the past: utilising information on population connectivity

Dispersal and population connectivity are very important species-specific

demographic parameters to consider when effectively designing a protected area

network (Dixo et al. 2009; Kininmoth et al. 2011). Population connectivity both

historic and recent can be inferred from the Fiji frog SNP and mtDNA tree

topologies (evidence for hybridisation can also be evaluated based on phylogenetic

expectations; see Chapter 5 - Discussion). The sharing of alleles between

populations via dispersal across geographical distances or barriers is often

discernable in the clustering of haplotypes and the short lengths of branches

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separating taxa (Sharma et al. 2010). Phylogenetic Diversity (PD; Faith 1992),

which measures patristic distances (sum of branch lengths) on phylogenetic trees,

provides a metric for drawing inferences of connectivity and also genetic

distinctiveness. For example, populations that cluster together on shorter branches

are more genetically similar, have low PD and share recent evolutionary history.

When genetically similar taxa are geographically disjunct, it is logical to assume that

these taxa or individuals are from populations that are ‘connected’ via dispersal.

Independently of trees, estimates of genetic distance such as the often used Kimura-

Nei estimate FST (Kimura 1980) can also tell us how much each population has

diverged from the nearest common ancestor. Given greater sampling depth, the FST

of Fijian frog populations could be estimated. However, in the absence of heavily

sampling Fijian populations, PD values provide a useful metric in this context.

Population connectivity is also best inferred from patterns determined from

both nuclear and mitochondrial markers as effective populations sizes of nuclear and

mitochondrial genomes differ, as do mutational rates in these genomes. Sequence

variation, and the PD of the molecular markers used in the present study was

relatively low, but sufficient to identify the genetic distinctiveness and connectivity

of populations. Genetic variation in the novel nuclear markers was more difficult to

interpret than that of mitochondrial markers, because of the unknown complexity of

their molecular evolution. Nevertheless, such markers can provide valuable insight

into genetic distinctiveness of populations as already discussed.

Knowledge of historic population connectivity has implications for

conservation: (1) ancestral connectivity can result in increased allelic diversity and

increased adaptive potential of populations (compared to genetically unique

populations with little to no past connectivity to other populations); and (2)

connectivity between geographically close but genetically unique populations would

suggest that dispersal pathways in the past and possibly the present are sufficient to

allow the mixing of genotypes. The results described in Chapter 4, suggest recent

expansion and population connectivity between Viti Levu and adjacent island

populations of C. vitianus, resulting in a lack of phylogenetic resolution between

individuals from these geographical locations. Populations of ground frogs on Vanua

Levu and Taveuni are notable by the extent of genetic divergence, and as such

suggest a possible source of origin for ground frogs. This is a hypothesis that could

be tested with additional sampling and sequencing.

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The measures of PD in Chapter 5 provide an objective framework for

decision making concerning ground frog populations. If the aim of future

translocation of populations was to source “locally”, then in the case of Viti Levu

ground frogs, local could mean from most populations in Viti Levu or even from

adjacent islands (Viwa and Ovalau). If genetic diversity was required (e.g. to

overcome inbreeding depression) then the genetic distinctiveness of populations in

Taveuni and Vanua Levu should be considered. Populations of C. vitiensis are

genetically diverse in both Viti Levu and Vanua Levu. This presumably reflects the

different population histories of ground and tree frogs. The later, presumably have

maintained distinct refugia in both Viti Levu and Vanua Levu during past periods of

Pleistocene climate change. This is a hypothesis that requires further testing. The

genetic distinctiveness of, and lack of apparent connectivity between some

populations highlights the importance of maintaining their current habitats, and the

value of the different locations as sources of genetic stock for future translocations if

inbreeding depression becomes a problem (Heber et al. 2012; Heber et al. 2013).

The above recommendations could represent a modified framework based on

Funk et al. (2012; see next section for description), where both nuclear and

mitochondrial (neutral and adaptive) markers are used to determine the Evolutionary

Significant Units (ESUs; Taveuni, Vanua Levu and Viti Levu), Management Units

(MUs; Vanua Levu and Viti Levu populations of both Fijian frogs), and

Conservation Units (CUs; Both species - Waisali Reserve, Driti, Natewa/Tunuloa,

Vunisea/Nakauvadra, C. vitiensis only- Namosi Highlands/ Serua, Matokana, and

Nadarivatu/ Tomaniivi).

6.4 INVESTIGATING THE ADAPTIVE POTENTIAL OF FIJIAN

CERATOBATRACHIDS

Until recently, most available conservation genetic studies have been based

on neutral markers that do not contribute to the ‘fitness’ of individuals in a

population (Holderegger and Wagner 2006). However, particularly with the advent

of NGS technology, interest is rapidly growing in markers under selection. In the

past decade, work has focused on adaptive genetic variation via quantitative genetic

experiments (crossings) that are carried out in a controlled environment (Bonin et al.

2007; McGuigan 2006). Anurans are ideal lab subjects for this kind of work as they

exhibit several life history features, such as explosive breeding cycles and external

128

fertilisation, which allow for controlled crossings (Beebee 2005). Adaptive genetic

variation is thought to be a better indicator of evolutionary potential, and it has been

debated over the last two decades, whether or not estimates of genetic variation

should be based on genes that code for traits that enhance overall fitness in a

population (Crandall et al. 2000). One thing that is clear is that estimates of PD can

differ markedly for neutral and non-neutral genes. Thus conservation decisions based

on PD can also differ depending on the nature of the molecular markers employed

(Becker et al. 2013).

Funk et al. (2012) described a ‘novel’ system of applying genomic

information to resolve this conservation genetics debate. The authors designed a

decision framework for the conservation of threatened species, where Evolutionary

Significant Units (ESUs) are first identified with all loci from genomic data (neutral

and adaptive) then Management Units (MUs) delineated with neutral loci, and finally

adaptive differentiation quantified among the MUs within the ESU. The framework

has been modified and applied in the conservation of exploited fish stocks (Bradbury

et al. 2013; Vincent et al. 2013; Larson et al. 2014); coral reef systems (Beger et al.

2014); forest tree species (Steane et al. 2014); endemic freshwater teleosts (Coleman

et al. 2013); and the iconic Giant panda (Ailuropoda melanoleuca; Zhu et al. 2013).

The basis for the framework is an acknowledgement that conservation units

(populations that are recommended for conservation effort) are best identified using

both neutral and adaptive genetic variation as population genetic history (a result of

genetic flow and drift) affects the genetic structure of populations, which is what

determines fitness of individuals and therefore the level of adaptive divergence.

Fitness traits have been studied in several anuran taxa and none more so than

Rana temporaria, the common European frog. Life history features such as growth

and larval development rates were previously well known, and quantitative genetic

experiments produced results which indicated all traits were heritable and either

additive (the expression of each allelic variant is completely independent) or non-

additive (Laurila et al. 2002). Fitness traits of anuran species that have been

investigated in studies on adaptive variation include egg size, size at metamorphosis,

and survival rates at different life stages. Other influences on adaptive variation have

been identified. Maternal effects, which are quantified by egg size, may affect larval

growth rates and metamorph size in R. temporaria populations (Laugen et al. 2002).

The size of eggs produced by mothers is in turn related to attributes of the

129

environment. Environmental selection has also been highlighted in studies on how

latitudinal gradients affect life history traits of R. temporaria (Palo et al. 2003).

More recently, research has centred around the concept that hybridisation

between closely related species under some circumstances can increase the adaptive

potential of hybrid offspring through the generation of novel phenotypes (Abbot et

al. 2013; Fraïsse et al. 2014). In frogs, hybridisation has been linked to increasing

colour polymorphism (see Chapter 5 discussion), an adaptive trait which confers

crypsis to tropical rainforest frogs (O’Neill and Beard 2010). Elucidating the

adaptive potential of Fiji’s frogs was outside of the scope of this thesis. However,

interesting questions are whether gene flow (hybridisation) between ground and tree

frogs has in the past facilitated adaptive diversification, and might again do so in the

future. The genetic signatures observed in analyses of novel nuclear markers

(Chapter 5) raise this possibility. Future research involving next generation

sequencing of Cornufer transcriptome and genomes might help to answer these

questions, and is being pursued elsewhere (Fraïsse et al. 2014).

6.4.1 The future potential of high throughput sequencing or NGS

Conservation efforts for endangered anurans are now benefiting from the

application of genomic approaches to adaptive and neutral genetic variation studies.

Microarray experiments, and more recently RNAS-seq methodology (Wang et al.

2009; Haas and Zody 2010), are helping researchers to determine what genes are

‘turned on’ or ‘turned off’ between individuals exposed to different treatments in a

quantitative genetic experiments (Koenig et al. 2013) and also under natural field

conditions (Voelckel et al. 2012) . Thus RNASeq has the potential to identify

adaptive markers (Hoffmann and Willi 2008) and will aid evaluation of inbreeding

depression and local adaptation to environmental change (Ouborg et al. 2010). An

enhanced understanding of adaptive markers that result in increased population

‘resilience’ would be of great use as applied using Funk and colleagues’ (2012)

framework for selecting populations for conservation and/or management (see also

the recent decision framework of Hoffman et al. 2015 and discussion of adaptive

markers).

Whole genome, and more practically, reduced representation sequencing of

whole genomes (e.g. Davey et al. 2010; Peterson et al. 2012) is also providing

similar insights. This research which is amenable to the study of non-model

130

organisms can help identify genetic variation which increases fitness in populations

exposed to environmental stresses and pathogens (Voelckel et al. 2012; Becker et al.

2013). Conservation genetics is beginning to make use of NGS technology to focus

on traits of adaptive significance, and as a result future conservation decisions should

be better informed as we are now in a position to identify individuals that are more

‘fit’ in certain situations, and translocating them to populations that are considered

genetically ‘depauperate’ in that sense (Storfer 2003; Funk et al. 2012). In

agricultural studies, geneticists are already considering the potential and planning for

crops under climate change scenarios (e.g. www.climatexchange.org.uk).

Neutral markers are useful in combination with more quantifiable genetic

variation, to determine the extent to which local effects (linkage hypotheses) and

general affects (global genomic hypotheses) influence the correlation between

genetic variability and fitness (Lesbarres et al. 2005). Assessing the ‘fitness’ levels

of different island populations of Fiji frogs would be advantageous in directing

possible translocation efforts if climate change adversely alters population

abundances and distribution (Weeks et al. 2011). Individuals from genetically ‘fit’

populations would be used to supplement or augment neighbouring populations that

have low genetic diversity between individuals.

The production of SNP assays on NGS sequencing platforms as described in

Chapter 5 has great potential for the conservation genetics of endangered anurans

and can help elucidate patterns in parentage analyses, and assist with the

identification and characterization of neutral and adaptive variation (Hess et al.

2015). Of particular interest will be the application of NGS to answer one of the

issues highlighted in Chapter 4 – how the rapid evolution of Neobatrachian

mitogenomes may have impacted on the dating of species divergences. The effect of

insufficient sampling on phylogenetic resolution will likely become a non-issue in

years to come as more frog mitogenomes are rapidly sequenced using NGS and

added to GenBank. Transcriptomics or more specifically RNA-SEQ analyses are

likely to become particularly useful for this application (Hoffman et al. 2015).

6.4.2 Hybridisation – adaption or threat?

As NGS grows in its applications for conservation genetics issues, an

important dispute may finally find closure. The debate surrounding the issue of

conserving or not conserving hybrids has been very polar. Hybrids were once

131

thought to have little or no conservation value (Richards and Hobbs 2015). More

recently, there is the suggestion that hybridisation will adversely affect the

persistence of species via ‘genetic swamping’ or the introduction of deleterious

alleles (Rhymer and Simberloff 1996; Pasachnik et al. 2009; Muhlfeld et al. 2014)

and may even lead to the eventual extinction of a species (Muhlfeld et al. 2014). On

the other hand there is evidence of ‘hybrid vigor’, which is thought to be

advantageous, which may serve to strengthen a species’ resistance to unsuitable

climates through novel phenotypic expression which can lead to ecological

diversification via the shifting of niches or formation of novel habitats (Rieseberg et

al. 2007; Rheindt and Edwards 2011; Becker et al. 2013), and may eventually lead to

speciation (Seehauseb 2004; Litsios and Salamin 2014). Debates can become heated

when one of the two species involved is a threatened species (e.g. as in the well-

publicized cases of the Red Wolf, Canis rufus, and the Florida panther [Hostetler et

al. 2013]). In light of these issues, the possibility of ancestral hybridisation between

C. vitiensis and C. vitianus is worth exploring in greater depth.

The genetic divergence present in both mitochondrial and nuclear genomes of

the two Fijian Cornufer species has had sufficient time, based on these estimates of

divergence, to evolve into reproductively isolating mechanisms (of which nothing is

known). Yet there is a possibility that populations of C. vitianus and C. vitiensis

were hybridising in the past; and if so might hybridisation for example, have been

important in the evolution of Taveuni ground frogs? In this case, what adaptive trait

transfers may have taken place? Were there corresponding changes in niche space,

associated with the transfer of adaptive traits? Is the level of polymorphism

associated with skin colour, a by-product of that event? Are there other cryptic traits

that may have been enhanced by hybrid vigor (traits which may eventually increase

both species’ resistance to potential threats, such as extreme temperature changes,

increased cyclonic intensity, disease outbreaks, further habitat degradation and loss,

etc.)?

6.4.3 Future Directions

The increasing number of whole mitochondrial genomes for anurans is

encouraging and a direct result of advances in NGS. Substitution saturation and

substitution model misspecification is however, an important issue concerning whole

mitogenome analyses, and is of great relevance for Neobatrachian phylogenetic

132

reconstruction given the levels of divergence observed in much of the recent

literature. The tendency for multiple substitutions and substitution biases to occur at

the 1st and particularly the 3rd codon positions in gene sequences, affects the accuracy

with which we estimate sequence divergence using molecular markers (Xia et al.

2003; Xia and Lemey 2009; Xia 2015).

Although many anuran phylogenetic analyses exclude the 3rd codon position

to account for substitution bias (as applied in this study), there is still a possibility of

saturation at the 1st codon affecting interpretation of trees; particularly for young

lineages that have undergone significant divergence driven by variable

environmental conditions of newly colonized habitats on island archipelagoes. The

inherent mutational bias of Neobatrachian mitogenomes (i.e. anuran genomes that

have undergone whole gene and/or genome duplications) that is a result of their

evolutionary history, has likely led to inaccurate estimations of phylogenies.

Furthermore, changes in possible evolutionary constraint at 2nd codon positions

between Neobatrachians and Archaeobatrachians remains relatively unstudied. The

value of NGS and the ever increasing suite of analytical software (e.g. DAMBE; Xia

and Xie 2001) to address the flaws in reconstructing phylogenies, particularly due to

substitution model misspecification, is an important direction of research that

promises to improve phylogenetic inference.

Future direction for research for the Fijian frogs would be to use new

emerging tools (such as those currently being implemented in BEAST), to account

better for lineage specific rates of substitution, as well as other approaches to better

evaluate model misspecification (Bouckaert and Lockhart, Pers. comm. 2015;

Goremykin et al. Pers. comm. 2015) on the dataset analysed here. The inclusion of

additional taxa more closely related to the Fijian Cornufer will also be informative in

determining the effect of site saturation and substitution model misspecification.

Determining this effect and sites most affected provides a means to eliminate

unrecognised bias in current phylogenetic interpretations. NGS has been

demonstrated as useful in the present and other studies. In particular, for generating

novel independent markers across genomes, useful for fine scale infra-specific

phylogenetic resolution (Twyford and Ennos 2012). The postulates of hybridization

offered in the preceding section directives could be more effectively addressed using

further NGS approaches:

133

i. Adaptive trait transfers and niche space - Quantitative trait loci (QTL)

mapping using high throughput SNP assays which is more commonly

tested on plant taxa (e.g. Whitney et al. 2015), but has been applied

successfully in freshwater teleosts (Selz et al. 2014). QTL mapping

requires the generation of hybrids using ex situ captive breeding.

Successful captive breeding of Fijian Cornufer has been proven possible

(Narayan et al. 2008; Singh, R. Pers. Comm. 2013), and it would be of

interest to see if genetically divergent populations on Taveuni and Vanua

Levu are capable of interbreeding, or whether reproductive isolation has

completely occurred between C. vitianus and C. vitiensis, and C. vitianus

Taveuni and other C. vitianus populations. In terms of developing high

density molecular markers for QTL or even genome wide association

studies (GWAS), GBS sequencing or similar protocols (e.g. ddRAD

sequencing) would be appropriate (Lin et al. 2015; Palaiokostas et al.

2015).

ii. Colour polymorphism (polychromatism) – The influence of introgressive

hybridization and regulatory variation on polychromatism in animals has

been highlighted in a recent review (Wellenreuther et al. 2014).

Comparative genomics has been applied on cichlids (Fan et al. 2012;

Maan and Sefc 2013) and crows (Poelstra et al. 2014) to investigate the

role of introgression and the maintenance of colouration patterns within

populations of hybrids. As skin colour is a polygenic adaptive trait, QTL

mapping of identified colour and associated trait loci (e.g. genes for sex

determination) would provide statistical support for conclusions from

prior comparative genomics research. The whole genomes of C. vitianus,

C. vitiensis, and the Taveuni C. vitianus populations have now been

sequenced, easing the initial process for future comparative genomics

using these and other published taxa.

iii. Hybrid vigor (heterosis) – A molecular understanding of increased

performance (e.g. in growth and fertility) of hybrids has been well

founded in plant crossbreeding experiments (e.g. Rosas et al. 2010;

Marques et al. 2011) but observable and quantifiable molecular analysis

of heterosis is rarer for animal taxa (e.g. Facon et al. 2005; Scriber 2013).

To determine if heterosis has played a role in the evolutionary history of

134

Fijian Cornufer captive breeding experiments would have to successfully

produce F1 generations and F2 backcrosses, which in turn will enable

Heterotic Trait Loci (HTL) analysis (as described in Ben-Israel et al.

2012). This avenue for further research is fairly new and would enable

the location and quantification of loci that confer hybrids an adaptive

advantage over parental phenotypes/ genotypes.

The Fijian frogs are undeniably an enigmatic branch of the Ranoidea and the

efforts made to conserve their habitats are a necessity in the writer’s opinion. There

is great potential for using these island frogs for exploring anuran mitogenome

evolution, for examining the role of adaptive divergence in generating unique

conservation units, and for investigating the potential role that hybridization has

played in generating polymorphic character traits that might confer adaptive

advantage. All of these interesting future research pathways have broader

implications for anuran conservation. It is exciting to think that soon we might have

answers to many questions concerning anuran biodiversity.

135

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APPENDIX A

GENBANK ACCESSION DETAILS FOR FROG MITOGENOMES

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Species GenBank Accession

Number Alytes obstetricans pertinax NC 006688 Ambystoma mexicanum AY659991 Amolops tormotus NC 009423 Andrias davidianus NC 004926 Ascaphus truei AJ871087 Bombina orientalis NC 006689 Buergeria buergeri AB127977 Bufo melanostictus AY458592 Ceratophrys ornata JX564858 Crinia signifera JX564860 Dendrobates auratus JX564862 Discoglossus galganoi NC 006690 Dyscophus antongilii JX564863 Eleutherodactylus atkinsi JX564864 Espadarana prosoblepon JX564857 Fejervarya limnocharis NC 005055 Gastrophryne olivacea JX564865 Gastrotheca pseustes JX564866 Hemisus marmoratus JX564868 Hyla japonica AB303949 Hylarana kreftii KM247362 Kaloula borealis JQ692869 Kaloula pulchra NC 006405 Leiopelma archeyi NC 014691 Leptolalax pelodytoides JX564874 Limnonectes bannaensis AY899242 Mantella madagascariensis AB212225 Microhyla heymonsi AY458596 Microhyla ornata NC 009422 Odontophrynus occidentalis JX564880 Paa spinosa FJ432700 Pelobates cultripes AJ871086 Pelophylax nigromaculatus AB043889 Phrynobatrachus keniensis JX564885 Phrynomantis microps JX564886 Pipa carvalhoi NC 015617 Cornufer vitianus KM247364 Cornufer vitianus Taveuni KM247361 Cornufer vitiensis KM247363 Polypedates megacephalus NC 006408 Quasipaa spinosa NC 013270 Rana catesbeiana KF049927 Ranodon sibiricus NC 004021 Rhacophorus schlegelii NC 007178 Rhinophrynus dorsalis JX564892 Sooglossus thomasseti JX564895 Tomopterna cryptotis JX564898 Xenopus tropicalis NC 006839

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