bio 585 coral reef field research methods
TRANSCRIPT
BIO 585 Coral Reef FieldResearch Methods
Reef biodiversity and evolution
Biodiversity
“…the millions of plants, animals, andmicroorganisms, the genes they contain,and the intricate ecosystems they helpbuild into the living environment.”
—World Wildlife Fund 1989
Biodiversity
“This definition is a bunch of
hooey. What we mean when we
say biodiversity is taxonomic,
usually species diversity.”
—McCartney 2004
Measures of species diversity
• species richness = S = the number ofspecies in a community or region
– pros:
• easy to survey and compare
• no need to census individuals
– cons:
• no information on relative abundance
• an incomplete measure of diversity
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Bird surveys at two tallgrassprairie sites in DeSoto NationalWildlife Refuge, Iowa.
Data from van Dyke (2003).
Species richness for the two sites issimilar (S site A = 8, for site B = 11)
But site A is dominated by 1species. Site B has greater“diversity” (abundances are moreeven). We need an index ofdiversity that reflects this.
Convert values to pi (proportion oftotal community abundancerepresented by i th species)
H' for site A = 1.64
H' for site B = 2.25
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Site A
Com
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Red
-win
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Pi
Site B′ = −∑H p pi i( ln )
Compute the Shannon index ofdiversity (H' )
E for site A = 0.789
E for site B = 0.938
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Site A
Com
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Red
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Pi
Site BE
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p p
Si ii=
′=−∑
ln
ln
ln
Or Pielou’s index of evenness (E )
The history of biological diversity
• the number of living species, in many groups,has increased steadily to the present
• this has been punctuated by major extinctions
Scleractinian corals appear
Modern-dayspecies diversity
Otheranimals281,000
Higherplants248,000
Protozoa30,800
Algae26,900 Fungi
69,000
Prokaryotes4,800
Viruses1,000
Insects751,000
• >1.5 million species havebeen described
• about 2/3rd’s are animals
• nearly half are insects
• from 4 to 150 times asmany remain undescribed
From Wilson 1992
Geographicpatterns of speciesdiversity on land
• species richness oftrees, ants, birds andmammals increasestowards the Tropics
• exceptions: conifers,bees, salamanders,waterfowl
Latitudinal patterns of marinebiodiversity
• species diversityincreases towards theequator in bivalves,tunicates, othersessile invertebrates,benthic forams
• exceptions: marinealgae, brittle stars,penguins
Explanations for increaseddiversity at lower latitudes
• higher solar radiation and primary productivityprovides greater resource base
• larger contiguous geographic area enhancesspeciation and retards extinction rates
• stability/time hypothesis: speciation has beenuninterrupted by glaciations; extinctions
• predictable tropical environment: greatercompetition, parasitism anddisease—promoting specialization andspeciation
Biodiversity “hotspots”
• small areas with a concentration of species
• contain many endemics, species foundnowhere else
due to their smallrange ofdistribution,endemics are veryvulnerable toextinction
Madagascar: 93% of primate,99% of frog species are endemics
From: Spaulding, MD et al. (2001) World Atlas of Coral Reefs.UNEP/WCMC and University of California Press, Berkeley CA.
The center of greatest diversity of scleractinian corals is theIWP, with gradients of decreasing diversity to the east and west
The Caribbean Sea holds the greatest concentration of speciesin the Atlantic Ocean
The IWP supports greater species richness in all coralreef animal taxa, and in associated ecosystems
One likely explanation for this is the much greater area of
reef coverage in the IWP, compared with eastern Pacific
and Atlantic regions
Positive species/area relationships are common interrestrial biogeographic studies, particularly on islands
This was a key finding that spurred the development ofisland biogeography theory (MacArthur and Wilson 1967)
Coral reefs and tropicalrainforests
the earth’s two most biodiversehabitats
Coral Reefs TropicalRainforests
Area (km2)(% global total)
284,3001
(0.1%)11,610,3502
(7%)
Animal Phyla(% global total)
32(94%)
9(26%)
Species(undescribed)
93,0003
(1-3 million)800,0004
(5 – 30 million)
Species per100 km2 area
33 7
Fishes(% of all marine)
40005
(25%)
Birds(% global total)
26006
(30%)
Land plants(% global total)
100,0007
(40%)
Sources of biodiversity estimates: 1Spaulding et al. 2001; 2Skole andTucker 1993; 3Paulay 1997, Reaka-Kudla 1997; 4May 1992; 5Ormondand Roberts 1997; 6Diamond 1985; 7Myers 1980.
Speciation on aBig Blue Planet:an Introduction
What is a species?
• a unit of discontinuity inthe living world
• an interbreedingpopulation: afundamental unit ofevolution
• a category of diversityworth conserving
Species concepts in biology
morphological species
phylogenetic species
biological species
Morphological species• the familiar
“taxonomic”description basedon sets ofdistinguishingcharacteristics
• often works butcan be misleading
from Futuyma (1998), p. 463
Morphological species of horned lizards
Morphological species
• these morphologically similarmeadowlarks cannot interbreed: theyare true species
Morphological species• these allopatric warblers were previously
classified as distinct species
• but they freely interbreed where they meet
Audubon’s warbler Myrtle warbler
Maps from USGS
Breeding range map of myrtle warbler
Breeding range map of Audubon’s warbler
The phylogeneticspecies concept:
species aremonophyletic
groups
[tips of the tree areindividuals, letters
denote populations]
Application of the phylogenetic concepthelped uncover cryptic species in thecopepod Eurytemora affinis
photo courtesy of SW Missouri State University
And inAfricanelephants
Biological species
• “...groups of interbreeding populationsthat are reproductively isolated from
other such groups...”
– Ernst Mayr
Biological species• the most widely
accepted and usefulspecies concept
• problems:
– useless for asexualorganisms
– sometimes difficult to test(e.g. allopatric species)
Biological species
• reproductive isolation: anobjective criterion that isbiologically significant
• application of the concept hasborn a research program
Understanding speciation?
study the evolution of reproductiveisolation
Reproductive isolatingmechanisms
• prezygotic mechanisms act priorto hybrid zygote formation
– behavioral (mate choice)
– gamete recognition
• postzygotic mechanisms act onhybrid zygotes
– hybrid inviability/sterility
– ecological inferiority of hybrids
Prezygotic: behavioral isolation
• courtship and mating behaviors diverge dramatically,even between closely related species
• Hawaiian Drosophila do not interbreed: females rejectcourtship of heterospecific males
Mating behaviors can evolve rapidly
• Drosophila heteroneura and D. silvestris are sisterspecies, sympatric on Hawaii
D. heteroneura has dumbbell-headed males that butt headswith other males to gain displayterritories on leks
from Fr eeman and Herron 2002
D. silvestris has roundy-headed males that fight othermales, Greco-Roman style,for territories
Behavioralisolation
• mating calls of frogsand insects arespecies-specific
• females recognizeconspecific calls
Prezygotic isolation due togamete incompatibility• marine
invertebrates andother organismsthat lack matingbehavior: speciesrecognition occursbetween egg andsperm
Sea urchin bindin: a gamete recognitionprotein involved in speciation
• Bindin is an adhesiveprotein that binds spermto the egg surface.Without this, fertilizationdoes not occur.
• Rapid change of bindinproteins creates barriersto fertilization betweenspecies.
Bindin
eggsurface
Postzygotic reproductiveisolation
• hybrids areoften inviable orsterile
Postzygotic reproductiveisolation
• hybrids are sometimes ecologically inferior
bird predation on hybridscreates abrupt boundariesbetween Heliconius colorraces
Yet hybridization in natural populations is widespread. Themost striking examples are where true species interbreedalong defined “hybrid zones.”
Hybrid zones are narrow and stable for many years. How doesthe zone persist, and how do the “parental species” maintaintheir integrity?
Mytilus edulis
Mytilus trossulus
Fig. 1. Frequency of M. edulis and M. trossulus i n the coastal Gulf of Maine (af terRawson et al. 2001). Insert: locati on of Gulf of Maine map and future proposed samplesi tes. A = Lunenburg, Nova Scoti a, B = Cobscook Bay, Maine, C = Dam ariscotta River,Maine, D = Nahant, Massachusetts, and E = Mysti c, Connecti cut.
Hybridzone
AllopatricM. edulis
Blue mussels in theMytilus edulis speciescomplex hybridizewherever species overlap
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M E T T E H T
Glu 5
Cobscook Bay, Maine,showing typical interstitialhabitat for mussels
These sibling species aretyped using 3 codominant
nuclear DNAs
The geography of speciation
• most speciesform whengeographicbarriers blockgeneticexchange
Allopatric speciation• arguably the most common way species form
• evidence for allopatric speciation is common inbiogeography:
– related species often occupy nearby, non-overlappingranges
Allopatric speciation• Isthmus of Panama closed
~ 3.1 MYA
• Isthmus closure split ~150“geminate” (twin) species
Evidence for allopatric speciation in snapping shrimps
Knowlton et al.(1993) created aphylogeny of Pacific (P) andCarribean (C) species pairs ofAlpheus
In 6 out of 7 cases, the closestrelative of a species was on theother side of the Isthmus
dispersal stops
An important avenue for allopatricspeciation is through “dispersal andcolonization”
genetic and reproductivedivergence of the colonists
Evidence from patterns ofspeciation in Hawaiian Drosophila
D. heteroneura
D. silvestris
• thought to explain species radiations on islands
Founder effect speciation
• divergence of a small population isolated onperiphery of range
Founder effectspeciation
• the genetic “founder effect” of small populationsize itself is thought to drive speciation
Sympatric speciation
• no geographic barrier
• much rarer
• yet, studies of sympatricspeciation show how ecologicalfactors, varying within acontinuous habitat, may drivespeciation by selecting forassortative mating
Sympatric speciation
• valid cases:
– cichlids in Camerooncrater lakes
– host races of Rhagoletis
(apple maggot fly)
Sympatric speciation: an example• Rhagoletis pomonella: the apple maggot fly
• larvae feed on natural host: hawthorn fruits
apples hawthorns
• a “host race” infesting apple trees appeared inNorth America ~150 years ago
Speciation in progress
• the apple race and hawthorn raceshave evolved reproductive barriers
striking geneticdifferences between theraces mark the earlystages of speciation
Adults mate and oviposit on their host trees
The classic “three stage”model of allopatric speciation• 1st stage: a geographic barrier
divides a large population into twoor more isolates
• 2nd stage: divergence of mating and/orhabitat preferences occurs in thedescendant populations
The classic “three stage” model ofallopatric speciation
• 3rd stage: reproductive isolation is completed, or “perfected”
– thought to be a crucial step, why?
• secondary contact is common on Earth
• without complete reproductive barriers, partially isolated species will fuse
During the “third stage” ofallopatric speciation...
• reproductive isolation can be completed intwo distinct ways
– as a byproduct of the divergence process
– via selection against hybridization(reinforcement)
Coyne and Orr’s (1997) surveyof Drosophila species pairs
• collected the following data from over 150species pairs, worldwide
– whether the species are allopatric or sympatric
– genetic distance between the species pair (basedon allozymes) as an estimate of its age
– the level of postzygotic and prezygotic isolation
Their results...
Prezygotic isolation increases steadily with genetic distance
Genes for prezygotic isolation diverge over time, just like the restof the genome
Their results...
Full isolation evolves in allopatry
Secondary contact is not necessary to complete the speciationprocess
Coyne and Orr’s (1997) survey supports reinforcement
Prezygotic isolation evolves faster in sympatry than in allopatry
Implies that selection against hybridization is powerful