EvolutionarilyStableStrategies(ESS)

6)Conditionalstrategies7)Tit­for­tatandtheevolutionofcooperation

2)Frequency­dependentselection3)TheHawk­Dovegame5)Alternativereproductivephenotypes4)SexratioasanESS8)Exampleexamquestions

1)TheESSapproach

Grafen(1991)calledthisthe‘phenotypicgambit’.Enoughmutationoccurstoalloweachstrategytheopportunitytoinvade.

Abodyofideasdevelopedtohelpunderstandevolutionaryprocesseswhennaturalselectionisfrequency­dependent.Selectionisrarelymeasured,buttheoryisusedtopredictphenotypesatequilibrium.

Thatpayoffsreflectthenumberofoffspringforeachallele;Somejargon(derivedfromgametheoryinmathematics):strategy:aprogramofaction;aphenotype;(termdoesn’timplygoal­directedbehaviorwhenappliedtonature)tactic:exercisingtheprograminaparticularsituationpayoff:fitnessApproachassumesthat:Theunderlyinggeneticsisthesimplestpossible;

1)TheESSapproach

WebofStories.WikimediaCommons­http://commons.wikimedia.org/wiki/File:John_Maynard_Smith.jpg#mediaviewer/File:John_Maynard_Smith.jpg

AsinglestrategyisanESSif,whenitisadoptedbymostmembersofthepopulation,itcannotbesupplantedbyamutant(rare)playinganalternatestrategy.DefinitionofESS: 1)TheESSapproach

JohnMaynardSmithwasamajorcontributortodevelopmentofthisapproachinthestudyofbehaviorandevolution(alsoFisher,Parker,HamiltonandMacArthurbeforehim).

H.melpomeneH.erato

postmanrayed

http://en.wikipedia.org/wiki/File:Heliconius_mimicry.png

Example:InHeliconiusbutterflies,100%postmanisanESS.Sois100%rayed.Wheneitherformismostcommon,theotherformcannotinvadewhenrare.The“payoff”(fitness)ofeach“strategy”(phenotype)dependsonitsfrequencyinthepopulation. 2)Frequency­dependentselection

3)TheHawk­dovegameFitnessof HD

WhenplayedagainstHDInventedtohelpdevelopourunderstandingoftheevolutionofaggressioninwildpopulations

Twostrategiesinthegame,HawkandDove;Hawk:fighttowin,retreatonlyifinjuredDove:Postureonly.Retreatifopponentescalates.

V0Fitnessof HDWhenplayedagainstHD

FromRose,M.R.andL.D.Mueller.2006.EvolutionandEcologyoftheOrganism.PearsonPrenticeHall.

3)TheHawk­dovegamePayoffmatrix

V0 V/2Fitnessof HDWhenplayedagainstHD

3)TheHawk­dovegame

(V­W)/2 V0 V/2Fitnessof HDWhenplayedagainstHD

3)TheHawk­dovegame

­25 500 25Fitnessof HDWhenplayedagainstHDExamplecase:V=50andW=100CanleadtoamixedESS:apolymorphismatequilibriuminwhichallstrategieshaveequalfitness3)TheHawk­dovegame

Lessonsfromthoughtexperiment:Aggressionhascostsaswellasbenefits;naturalselectiondoesnotnecessarilyleadtotheevolutionofpureaggression;noneedtoappealto‘thegoodofthespecies’toexplaindove­ishnessinnature.

MixedESSAsinglestrategyisanESSif,whenitisadoptedbymostmembersofthepopulation,itcannotbesupplantedbyamutant(rare)playinganalternatestrategyAmorecomplexpossibilityisamixedESS,inwhicheitheroftwostrategiescaninvadewhenrare.Atequilibriumfrequency,thepopulationispolymorphicandbothstrategieshaveequalfitness.Atequilibrium,neitherstrategyhasafitnessbenefit.

Conover&VanVoorhees(1990)Control

http://filaman.ifm­geomar.de/Photos/PicturesSummary.php?ID=339&what=species

TheAtlanticsilversidehastemperature­dependentsexdetermination

Proportionoffema

les

4)SexratioasamixedESS

Control

Conover&VanVoorhees(1990)Proportio

noffemales

4)SexratioasamixedESSButthetemperaturethresholdatwhichmalesorfemalesareproducedcanevolve.

http://www.eurekalert.org/multimedia/pub/19443.php?from=151980

Whenisaroughly50:50sexrationotobserved?1)Cytoplasmicfactors(e.g.,Wolbachia)2)Spatialstructure(e.g.,Nasonia)3)Sex­specificlifehistories(e.g.,Seychelleswarbler)

4)SexratioasamixedESS

Nasoniavitripennislifecycle Femalesflyoffandlaybroodofeggsinafreshflypupa

Larvalwaspsdevourfly,growbig,pupate

Youngwaspsemergeandmateonthepupabeforeflyingoff.Malesareflightless. ©PeterKoomen

http://www.spektrum.de/alias/interview/gene­lesen­ist­erst­die­halbe­miete/1021808https://www.wageningenur.nl/en/show/Bart­Pannebakker­The­evolution­of­reproductive­modes­in­parasitoid­wasps.htm

4)SexratioasamixedESS

Whenonlyonefemalelayseggsonasinglehostpupa Whenmultiplefemaleslayeggsonasinglehostpupa

Shelaysmoremanydaughtersthensons Sexratiooftheiroffspringiscloserto50:50

4)SexratioasamixedESS

Theleadinghypothesistoexplainthisphenomenonislocalmatecompetition(LMC).Whenmatingtakesplacelocally,brotherscompeteforfemales.Thisreducesthefitnessbenefitstofemalesfromproducingmaleoffspring.

http://www.eurekalert.org/multimedia/pub/19443.php?from=151980

Proportionmalese

merging waspsper10hosts

waspsper20hosts

Wylie(1965)

Velthuisetal(1965)

4)SexratioasamixedESS

SexratioadjustmentintheSeychelleswarbler

Komdeuretal(1997)Nature

Proportionmalene

stlings

Territoryquality

Hypothesis:femaleoffspringremainonterritoryandhelpparentsraisenextbroods.Thisisanetbenefittoparentswhenterritoryqualityishighbutnotwhenqualityislowbecauseofgreatercompetitionforfood.

5)Alternativereproductivephenotypes

Gross(1996)TREE

http://en.wikipedia.org/wiki/Bluegill

Polymorphisminbluegillsunfish5)Alternativereproductivephenotypes

ParentalmorphMalebuildsnest,attractsfemalesRemainsatnestafterspawningYellow­orangebreast.ExhibitspaternalcareAggressive,large5)Alternativereproductivephenotypes

Small,nobreastcolorDartsinduringspawning,releasesspermInLakeOpinicon,fertilizesanaverageof89%ofeggsinthe8%ofspawningeventsinwhichtheyparticipateSneakermorphHidesnearnestofparentalmale

5)Alternativereproductivephenotypes

SatellitemorphHoversabovetheparentalmaleandspawningfemaleSlowlydescendsnextto(oftenbetween)theparentalmaleandfemale,mimickingfemalebehaviorbutreleasingspermMimicsafemaleincolorandbehavior5)Alternativereproductivephenotypes

IsitamixedESS?Notknown.Twobasicstrategies:Parentalandcuckold(sneakersandsatellites)SneakersdevelopintosatelliteswithageButneitherparentalnorcuckoldmorphdevelopsintotheother.RelativenumbersinLakeOpinicon:64%sneakers21%satellites15%parentalmales85%!!

5)Alternativereproductivephenotypes

5)Alternativereproductivephenotypes~3.8MYAAncestralchromosome

~InversioneventAccumulationofgeneticchangesincludingthreedeletionsaroundSDR17B2andHSD42E1AccumulationofgeneticchangesFurtheraccumulationofgeneticchangesRecombinationevent(s)(~520,000yearsago)FurtheraccumulationofgeneticchangesSatelliteIndependent Faeder

Furtheraccumulationofgeneticchanges

Lamichhaneyetal.(2016)NatureGenetics;Taylor&Campagna(2016)Science

Asupergeneunderliesthemalepolymorphisminruff.Theinversionbreakpointdisruptsagene,withtheresultthatindividualshomozygousfortheinversiondie.ThishasastrongeffectontheESS.Doweneedtoknowthegenes?

Alternativemalereproductivephenotypesinnatterjacktoad

www.ecologyservices.org/images/DANoothSB0051.jpg

AverageObservedfrequencymatings67%80.5%33%19.5%CallersSatellites

ApparentlynotamixedESS–conditionalstrategyinstead6)Conditionalstrategies

Arak(1988)AnimalBehaviour

7)Titfortatandtheevolutionofcooperation[intentionallyleftblank]

8)ExampleexamquestionsProvideanexampleoffrequencydependentselection.Howmightyoutestwhetherfrequency­dependentselectionisoccurringonapolymorphicpopulations?Whymightweexpectnaturalselectiontoresultinanequalsexratio(1:1forsons:daughters)inarandomly­mating,diploidpopulations?Underwhatcircumstancesmightnaturalselectionfavorasexratiothatisbiasedinfavoroffemales?Explain.Amarinepopulationofcuttlefishhastwomalereproductivemorphs,“territorial”and“femalemimic,”occurringatfrequency60%and40%respectively.DesignanexperimenttotestwhethertheobservedfrequenciesrepresentamixedESS.HowmighttheunderlyinggeneticbasisofanESSaffecttheequilibriumfrequenciesofalternativemorphs?

Givethedefinitionofanevolutionarilystablestrategyandprovideanexample.