Clonal diversity mattersHigh levels of functional and genetic

diversity occur in the model microzooplankter Oxyrrhis marina

SSchool chool of of

BBiological iological SSciencesciencesSSchool chool of of

BBiological iological SSciencesciences

Chris Lowe, David Montagnes, Phill Watts

Microbial food webs are important in aquatic systems

Many morphospecies are thought to be ubiquitous

Phylogenetic data suggest this may be so (but results are ambiguous)

But are we looking at the right aspects?

Functional (phenotypic) diversity may be a more appropriate metric to assess distribution

Introduction

Redrawn from Conover (1982)

A well characterised morphospecies

A commonly used model organism

An easy organism to grow

Ubiquitous

Introduction: Oxyrrhis marina Dujardin 1859

10 µm

Distribution

“Everything is everywhere, nature selects”Are we adequately examining diversity?

MorphologyGeneticsFunctional differences (phenotypes)

Introduction: The BIG question

A specific test case: O. marina One morphospecies Phylogenetic markers (different)Ecophysiological responses (different)

Phylogeography: Distribution

Phylogeography: Our data

Phylogeography: (5.8s ITS rDNA)

18s 5.8s 24s

5` 3`ITS ITS

0.05 substitutions/site

Plymouth CAP1133/3

IOM/PSM

IOM/P

IOM/S

Bahrain CAP1133/4

Finland CCAP1133/5

Washington CCMP604

Caribbean CCMP1788

Connecticut CCMP1795

Florida CCMP605

Texas CCMP1739

100

100

100100

95

63

These are all Oxyrrhis (18s rDNA)

4 well-supported cladesLarge genetic differencesDo they have a phylogeographic

distribution?Lowe et al. 2005

Phylogeography: (5.8s ITS rDNA)

They have no clear phylogeographic distribution

Ecophysiology: Is distribution related to function?

Ecophysiology: Is distribution related to function?

Habitat Environment

Oxyrrhis marinaPools vs coastal watersSalinity

SalinityG

row

th r

ate

()

Salinity (ppt)

10 6030 40

0

1

-1

Time

nu

mb

ers

Nt = N0•et

Ecophysiology: salinity

Salinity (ppt)

Gro

wth

rat

e (

d-1)

Location

Geographical location

5.8s ITS sequence data

Habitat: coastal, intertidal

Ha

bit

at

Co

as

tal

There appears to be a habitat specific response

Ecophysiology and rDNA do not agree

2 growth rate responses

Lowe et al. 2005

Morphology: inadequate resolution “Neutral” markers: rDNA does not

explain observed distribution of clones

Is everything everywhere?

We need to examine multiple clones to assess differences

Ecophysiology: suggests distributional patterns based on habitat

Our next step is to examine:Selection/adaptation Population

structure/dispersalNeutral and Functional

characteristics

Interdisciplinary approach to biodiversity

Redrawn from Conover (1982)

Conclusion

Breaking boundaries: quantifying the influence of demography and

seascape in driving divergence in the protist Oxyrrhis marina

Phill Watts, Chris Lowe, David Montagnes

SSchool chool of of

BBiological iological SSciencesciencesSSchool chool of of

BBiological iological SSciencesciences

This is a hypothesis describing processes of:DispersalAdaptation

Oxyrrhis marina:

“Everything is everywhere, nature selects”

It suggested distributions of micro-organisms are fundamentally different from macro-organisms

To data there has been no explicit tests of this hypothesis for micro-organisms across landscapes

Distinct oceanographic boundaries (e.g. fronts, gyres, isthmuses, currents)

Strong environmental gradients (temperature, salinity)

The marine environment is heterogeneous

We will quantify relative roles of natural selection and random drift in driving divergence

Spatial variation in adaptive traitsi.e. salinity and temperature tolerance

Demographic parameterse.g. population boundaries, population sizes migration rates

Are these processes/parameters different between micro-organisms and macro-organisms?

Oxyrrhis marina:

The heterogeneous marine environment provides a framework to examine adaptive/neutral variation

Oxyrrhis marina and the marine environment

Collect O. marina samples from across Europe

2 scales: Northern EuropeIrish and Celtic seas

For each site:Isolate & culture replicate O. marina clones Genotype isolatesMake phenotypic measurements Growth rate Cell size Gene expression (Na/K ATPase, HSP)

Oxyrrhis marina and the marine environment

Gene expression

Gen

etic

an

d p

hen

oty

pic

div

ersi

ty

Cycle number20 25 30 35

Flu

ore

sce

nce

t1

r1

t2

r2

MicrosatelliteGenotyping

Na

/K A

TP

ase

e

xpre

ssio

n

Salinity

Population growth rate

Time

Nu

mb

ers

Salinity

Nt = N0•et

Temperature

morphology

Fst

Qst

Fst (dispersal)

Measures of the extent of divergence between populations relative to the total diversity within all populations

Based on neutral markers (e.g. microsatellites)Provides an indication of geneflow/dispersal between

populations

HT = heterozygosity in total population

HS = average heterozygosity in subpopulationsT

STst H

HHF

)( )(2

)(2

)(2

wpbp

bp

stQ

σ2

p(b) = phenotypic variancebetween populations

σ2p(w) = average phenotypic

variance within populations

Qst (adaptive divergence)

Measures of the extent of divergence between populations relative to the total diversity within all populations

Based on phenotypic traits (e.g. ecophysiological responses, morphometrics)

Provides an indication of adaptive divergence

1)( )(

2)(

2

)(2

)(2

)(2

wpbp

bp

st

wpbp

Q

0)( )(

2)(

2

)(2

)(2

)(2

wpbp

bp

st

wpbp

Q

Qst

)( )(2

)(2

)(2

wpbp

bp

stQ

σ2

p(b) = phenotypic variancebetween populations

σ2p(w) = average phenotypic

variance within populations

Salinity

Salinity

Fst – Qst: comparisonNo dispersal barriers Fst↓Identical environments Qst ↓

Fst

Qst

(popns connected, no adaptive divergence)

0 1

(popns different, no adaptive divergence)Balancing selection

Complete dispersal barrier Fst ↑Identical environments Qst ↓ Fst

Qst0 1

No dispersal barriers Fst↓Different environments Qst ↑

Salinity

Fst

Qst

(popns connected, adaptive divergence)Spatially varying selection

Salinity

Fst – Qst: comparison

0 1

Complete dispersal barrier Fst ↑Different environments Qst ↑

(popns different, adaptive divergence)

Fst

Qst0 1

Gene expression

Gen

etic

an

d p

hen

oty

pic

div

ersi

ty

Cycle number20 25 30 35

Flu

ore

sce

nce

t1

r1

t2

r2

MicrosatelliteGenotyping

Na

/K A

TP

ase

e

xpre

ssio

n

Salinity

Population growth rate

Time

Nu

mb

ers

Salinity

Nt = N0•et

Temperature

morphology

Fst

Qst

So, all we need to do is:

1.Collect many O. marina

2.Make measurements on neutral markers and phenotypic traits

3.Compare Fst-Qst

4.Apply data to landscapes and boundaries

5.Test hypothesis that everything is everywhere and nature selects

But it’s expensive to travel all over the place and would make a big carbon footprint

Solution: we need your help to collect O. marina

Oxyrrhis marina and the marine environment