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