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Lecture 7

ANTH 201 Lecture Notes - Lecture 7: Parapatric Speciation, Sympatric Speciation, Allopatric Speciation


Department
Anthropology
Course Code
ANTH 201
Professor
Susanne Cote
Lecture
7

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Speciation
MicrovsMacroevolution
● Microevolution
○ Evolutionwithinpopulations
,withinspecies
○ Changesinallelefrequenciesandassociatedtraitswithinpopulations
● Macroevolution
○ Evolutionofspecies,genera,families,andotherhigherorderlevelsof
classification
○ Relevanttointerpretthefossilrecord
SpeciesConcepts
● Speciesarebasicunitsofanalysisformacroevolution
● Individualsbelongingtoaspeciesaresimilartooneanother,distinctfromothers
● Weusuallyhaveanintuitivesenseofwhatspeciesare,butcanbedifficulttodefine
BiologicalSpeciesConcept(BSC)
● Mostpopulardefinitionamongevolutionarybiologists
● Species=agroupofactuallyorpotentiallyinterbreedingorganismsthatis
reproductivelyisolatedfromothersuchgroups
● Reproductiveisolationcannotmatesuccessfullyoutsidethegroup
○ Isolatingmechanisms:geographicseparation,differencesinbehaviour,physical
appearance,numberofchromosomes,reproductivephysiology,...
○ Nohybridization(geneticexchangebetweendistinctpopulations)
■ Orhybridsdie
oraresterile
○ Requiresabarriertogeneflowbetweengroups
GeneFlow
● GeneFlow:themovementofgeneticmaterialwithinorbetweenpopulations
○ Maintainssimilaritiesamongmembersofthepopulation(s)
○ Counterstheeffectofselectionfordifferentphenotypes
■ e.g.ifallelesareselectedagainstinonepartofthepopulation,theymay
stillreappearthroughmigration
BSCandGeneFlow
● Lookingatthefinches(cangobetweenwetanddryhabitats)
○ Migrationpossiblebetweenhabitats
○ Geneflowswampslocaladaptation

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○ Phenotypeintermediate
○ 
● Finchescannottravelbetweenwetanddryhabitats
○ Migrationnotpossible
○ Nogeneflow
○ Localadaptationsfavoured
○ Phenotypesbecomedistinct
○ Speciesreproductivelyisolated
EcologicalSpeciesConcept
● Species=lineagethatoccupiesadaptivezone(ecologicalniche)differentfromthatof
anyofotherrelatedlineage
● Barriertogeneflow(reproductiveisolation)isneithernecessarynorsufficientto
maintainspeciesboundaries
● Naturalselectionplaysroleinmaintaining(andmaybecreating)differencesbetween
species
● Example
○ AdaptivePeaksinfinches
■ Foodsourcesnotevendistributed3mainsizeclassesofseeds
■ Threedistinctbeaksizescanexploitthese3seedtypesbest
■ Despitegeneflow,threetypesmaintained
● Naturalselectionagainsthybrids
● Eachspeciesofgroundfinchexploitsadifferentecologicalniche
○ Threebeaksizesbestadaptedforthreeseedsizes
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