spatial heterogenity, evolutionary diversification, mutation and strong dynamics

spatial heterogenity, evolutionary diversification, mutation and strong dynamics

Evolution instructuredpopulations:
beyond thekinversusgroupdebate
Se´ bastien Lion1*, VincentA.A.Jansen1 and TroyDay2
1 School ofBiologicalSciences,RoyalHollowayUniversityofLondon,EghamTW200EX,UnitedKingdom
2 Departments ofMathematics,StatisticsandBiology,JefferyHall,Queen’sUniversity,Kingston,ON,K7L3N6,Canada
Much oftheliteratureonsocialevolutionispervadedby
the olddebateabouttherelativemeritsofkinandgroup
selection. Inthisdebate,thebiologicalinterpretationof
processes occurringinrealpopulationsisoftenconflat-
ed withthemathematicalmethodologyusedtodescribe
these processes.Here,wehighlightthedistinctionbe-
tween thetwobyplacingthisdiscussionwithinthe
broader contextofevolutioninstructuredpopulations.
In thisreviewweshowthatthecurrentdebateoverlooks
important aspectsoftheinterplaybetweengeneticand
demographic structuring,andarguethatacontinued
focus ontherelativemeritsofkinversusgroupselection
distracts attentionfrommovingthefieldforward.
It’s likewhatLeninsaid. . . you lookfortheperson
who willbenefit,and,uh,uh. . .
–The Dude
Kin versusgroupselection
Recentyearshaveseenarevivalofinterestintheevolution
of structuredpopulations,withastrongemphasisonthe
evolutionofsocialtraitssuchasaltruisticandcooperative
behaviours [1–5]. Thishasreignitedthedebateonkin
versusgroupselectionandhasgeneratedmuchdiscussion
abouttheprocessesunderlyingtheevolutionofsuchtraits,
as wellasthemostappropriatemodellingformalism [6–9].
Muchofthisrecentdiscussionhasdivertedattentionfrom
importantbiologicalissues,andourgoalhereisthereforeto
placethisdebatewithinthebroadercontextofevolutionin
structuredpopulations.Insodoingwehighlightthefact
thatinastructuredpopulation,virtuallyalltraitscanbe
thoughtofassocial,includingdispersal [10], life-history
traitssuchasreproductiveeffort,senescenceandsexallo-
cation [11], andvirulenceorresistancetraitsinhost–para-
siteinteractions [12,13].Withinthisbroaderperspectivewe
pointoutpossibleavenuesforfutureresearch.
What isthedebateabout?
Thecurrentdebateseemstostem,inpart,fromafailure
to clearlydistinguishbetween thebiologicalinterpreta-
tion ofprocessesoccurringinrealpopulationsand
the mathematicalmethodologyusedtodescribethese
processes.Thetwoarenecessarilyintertwined,butit
cansometimesbeusefultodistinguishbetweenthem.
To thisend,weusethetermskinselection(KS)and
multilevel selection(MS)todescribetwodifferentbiologi-
calinterpretationsoftheevolutionaryprocessesoccurring
instructuredpopulations,andthetermsinclusivefitness
(IF) methodologyandmultilevelselectionmethodologyto
describe themathematicalapproaches typicallyusedwith
each.
General background
Whenever anindividual’sreproductivesuccessisaffected
by traitsexpressedbyotherindividuals,weneedtoac-
count forthewayinwhichgenotypesaredistributed
among individualstopredictevolutionarychange.The
IF andMSmethodologiesaredifferentwaysbywhich
theoreticians accountforthisgeneticstructure.
As anexample,consideracaseinwhichallindividuals
in thepopulationprovidesomelevelofhelpto n other
individuals, andsupposethatamutantallelearisesthat
causes itsbearertoprovideanincreasedlevelofhelpata
cost toitself.Todetermineiftheallelewillspread,weneed
to calculatetheselectioncoefficient,whichisthedifference
between theaveragereproductiveoutputsofindividuals
carrying themutantversuswild-typealleles.Theaverage
reproductive outputsaredifficulttocalculatebecauseof
the spatialstructureofthepopulation.Infact,thisdiffi-
culty arisesfortworeasons:(i)whencalculatingtheaver-
age reproductiveoutputsforbearersofeitherallele,we
need toknowtheprobabilitythatitsneighbourscarrythe
same allele;and(ii)theprobabilitythatitsneighbours
carry thesameallelewilltypicallydependontheactionof
the allele.Forexample,iftheallelecausesahigherlocal
level ofreproductiveoutput,thenitsneighboursmightbe
very likelytocarrythisalleleaswell.Thesecomplications
typically precludeanalyticalprogressunlessfurthersim-
plifying assumptionsaremade.
IF andMSmethodologies
The IFmethodology(Box 1 and online appendix S1) parti-
tions theselectioncoefficientintoadirectandanindirect
selection component [14–17]. Thedirectselectioncompo-
nent accountsfordifferencesinthedirecteffectsofthe
allele onitsbearers’reproductivesuccess.Inourexample
this isnegativebecausethemutantallelecausesitsbearer
to providemorehelpthanthatofthewild-type,atacostto
itself. Theindirectselectioncomponentaccountsfordiffer-
ences betweenmutantandwild-typeindividualsinthe
Review
Corresponding authors: Lion, S.(lion@cefe.cnrs.fr); Jansen,V.A.A.
(Vincent.Jansen@rhul.ac.uk); Day,T.(tday@mast.queensu.ca)
* Present address:Centred’E´ cologie FonctionnelleetE ´ volutive, UMR5175,CNRS
1919 routedeMende,34293MontpellierCedex5,France
TREE-1342; No.ofPages9
0169-5347/$ – see frontmatter  2011 ElsevierLtd.Allrightsreserved.doi:10.1016/j.tree.2011.01.006 Trends inEcologyandEvolutionxx(2011)1–9 1

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