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Altruism in insect societies and beyond voluntary or enforced Francis L Altruism in insect societies and beyond voluntary or enforced Francis L

Altruism in insect societies and beyond voluntary or enforced Francis L - PDF document

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Altruism in insect societies and beyond voluntary or enforced Francis L - PPT Presentation

W Ratnieks and Tom Wenseleers Laboratory of Apiculture and Social Insects Department of Animal and Plant Sciences University of Shef64257eld Shef64257eld S10 2TN UK Laboratory of Entomology Zoological Institute Catholic University of Leuven 3000 Leuv ID: 35321

Ratnieks and Tom Wenseleers

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Altruismininsectsocietiesandbeyond:voluntaryorenforced?FrancisL.W.RatnieksandTomWenseleersLaboratoryofApicultureandSocialInsects,DepartmentofAnimalandPlantSciences,UniversityofShefÞeld,ShefÞeld,S102TN,UKLaboratoryofEntomology,ZoologicalInstitute,CatholicUniversityofLeuven,3000Leuven,BelgiumThealtruismofinsectworkershaspuzzledresearchers :asituationwherebycoercionfavoursindividualstocomplywiththesocialnormsofthegroup,evenifthisisnottheirfirstchoice[7].:anactionthat,onaverage,decreasesthelifetimedirectfitnessofanactorandbenefitsoneormorerecipients[4].:socialpressureintheformofthepunishmentorpolicingofgroupmembers,usuallytopreventthemfromactingselfishlyandtherebyharmingthegrouporcolonyasawhole;thewordsenforcementandsanctionhavesimilarmeanings[5].Enforcedaltruism:altruism,orthelevelofaltruism,favouredbynaturalselectionactingonindividualsinsocialgroupswithcoercion[14].:socialgroupsinwhichsomeindividualsspecialiseinworkorhelpingtoenhancethedirectreproductionofothers.HamiltonÕsrule:theinequalityarisingfromW.D.HamiltonÕsinclusivefitnesstheory[4]thatpredictswhenasocialaction,suchasaltruism,is Correspondingauthor:Ratnieks,F.L.W.(F.Ratnieks@Sheffield.ac.uk0169-5347/$Ðseefrontmatter2007ElsevierLtd.Allrightsreserved.doi:10.1016/j.tree.2007.09.013 societies,includingvertebrateandhumansocieties,andinterspeciÞcmutualisms.FamilylevelsofrelatednessareinsufÞcientforcompletevoluntaryaltruismHamiltonÕsruleshowsthathigherrelatednessfavoursgreateraltruismaltruism.Inhymenopteraninsectsocietiesheadedbyasingle,once-matedqueen,sistersarehighlyrelated,by0.750.75.However,aretheobservedlevelsofrelatednesssufÞcienttoexplaintheextremeworkeraltru-ismobservedinmanyinsectsocieties?Forexample,intheApismellifera,queensmatewithabouttenmales,andworkersarerelatedbyonly0.30.3.Howcanthislowlevelofrelatednessresultinsocietiesinwhichfewerthanonein1000workersattemptstolayeggseggsoronein10000femalelarvaedevelopsintoaqueenqueen?Recenttheorysuggeststhat,intheabsenceofcoercion,itit.Thereasonbecomesclearwhenweconsideregglayingbyworkersworkers.InthesocialHymenoptera,workerscanlayhaploid,male-destinedeggs(Figure2).Theyareselectedtodosobecausetheyaremorerelatedtotheirownsonsthantosonsofeithertheirmotherqueenorsistersister.Nevertheless,notallworkersareselectedtoreproduce.Ifallworkerslaideggs,therebyleavingnonetowork,thecolonywoulddieandtheinclusiveÞtnessofeveryindividual,includingtheegglayers,wouldbezerozero.Theequilibriumproportionofworkersthatshouldreproduce,intheabsenceofcoercion,canbedeterminedfromHamiltonÕsrulerule(Box1)andis14%forspeciessuchasstinglessbeesorbumblebees,inwhichqueensmatewithasinglemalemale,and54%forthehoneybee.Importantly,theseÞguressuggestthattheintermediaterelatednesslevelsfoundininsectsocietiescannotcausetheextremealtruismfoundinthehoneybeeandmanyotherspecies,inwhichveryfewworkersreproduce.Theory,however,alsoshowsthatthesehighlevelsofworkeraltruismcanoccurifthepotentialaltruistsarecoerced,thatisifaltruismisenforced.Inthehoneybee,workersselectivelykillorpoliceeggslaidbyotherworkersworkers.Theoryshowsthatsuchpolicingcanreducetheincen-tiveforworkerstolayeggstosuchanextentthatfew,orevennone,shouldevenattempttodososo.Evidenceforenforcedaltruism:egg-layingbyworkersAlthoughworkerpolicingwasÞrstdiscoveredinthehon-[6],ithassincebeenfoundinseveralotherant,beeandwaspspecies[5,18].Thekillingofworker-laideggsbythequeen(queenpolicing)isalsowidespreadandisparticularlycommoninspecieswithsmallcoloniesolonies.Ifpolicingdoescoercealtruismbyreducingtheopportunityforworkerstoreproduce,wepredictthatfewerworkersshouldlayeggsinspecieswithmoreeffec-tiveeggpolicingg.Recently,acomparativestudyoftenspeciesfoundstrongsupportforthisprediction:speciesinwhichworker-laideggshadagreaterchanceofbeingkilledhadsmallerproportionsofegg-layingng(Figure3Thedeterrenteffectofcoercionhasalsobeenshownbycomparingworkerreproductionincolonieswithandwith-outaqueenqueen(Figure3).Inqueenlesscolonies,policingisabsent,andalastbatchofworker-derivedmalesisrearedbeforethecolonydiesout.Inqueenlesshoneybee40%oftheworkerslayeggseggs.ThisproportionisclosetotheinclusiveÞtnesstheorypredictionbasedonvoluntaryaltruismalone(54%,Box1)andgreaterthanthe0.01Ð0.1%thatreproduceincolonieswithaqueenqueen.Queenlesscoloniesgiveanideaofwhatinsectsocietieswouldbelikeifenforcementwereabsentandaltruism Figure1.EnforcedcooperationininsectandvertebratesocietiesandinterspecificWorkerpolicingpreventsworkersfromreproducingintheApismelliferamellifera;(b)queenpolicing(inset)preventsmostworkersfromreproducingsuccessfullyinthebumblebeeBombusterrestristerrestris;(c)aworkerwithactiveovariesisaggressedinthequeenlessantHarpegnathossaltatorsaltator;(d)inthehoneybee,differentialfeedingforcesmostlarvaetodevelopasworkers;onlylarvaerearedinroyalcells(arrow)candevelopasqueensqueens;(e)subordinateworkersfromtheallodapinebeeExoneurabicolorareevictedfromthenestwhentheyhavebeenincontactwithaforeignmalemale;(f)aworkerthatattemptedtooverthrowthebreederfemaleispunishedinthequeenlessantDinoponeraquadricepsquadriceps;(g)inthecooperativelybreedingcichlidNeolamprologuspulcher,subordinatesthatdonothelplookaftertheeggsandfryareevictedevicted;(h)rhesusmonkeys(Macacamulatta)whodonotsharefoodarepunishedpunished;(i)inmeerkats(Suricatasuricata)dominantfemalespreventsuccessfulbreedingbysubordinatessubordinates;(j)soybeanplants(Glycinemaxsanctionrootnodulebacteriathatdonotfixnitrogen,asshownbythissplitrootexperimentexperiment.Reproduced,withpermission,fromF.L.W.Ratnieks(a,d),theBBCNaturalHistoryUnit(LifeintheUndergrowthseries)(b),J.Liebig(c),M.Schwarz(e),T.Monnin(f),J.Desjardins(g),M.Hauser(h),A.Young(i)andB.Rousseau(j). TRENDSinEcologyandEvolutionVol.23No.1