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Author:Poole, Chris

Title:Investigating the Interactions between Social Behaviour and Habituation to a NovelEnvironment in Sticklebacks (Gasterosteus aculeatus)

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InvestigatingtheInteractionsbetweenSocialBehaviourandHabituationtoaNovelEnvironmentinSticklebacks(Gasterosteusaculeatus)

ByChrisPoole

AdissertationsubmittedtotheUniversityofBristolinaccordancewiththerequirementsforawardofthedegreeofMastersbyResearchin

BiologicalSciencesintheFacultyofScience.

SchoolofBiologicalSciencesSeptember2018

WordCount:18,404

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AbstractThisthesisaimstoinvestigatetheinteractionsbetweenthecollectivebehaviourofsticklebacks(Gasterosteusaculeatus)andtheratetowhichtheyhabituatetoanovelenvironment.Thefirstdatachapterisagroup-basedstudy,whichinvestigatestherateatwhichgroupsofvaryingcohesivenesshabituatetoanovelenvironment.Groupsofeightindividualswereintroducedintoatankcontainingtworefugesandanopenarea,whichwasassumedtocarryahigherperceiveddegreeofpredationriskthantherefuges.Therewasfoundtobeapositivecorrelationbetweengroups’cohesivenessandthedegreetowhichtheyhabituatedtothenovelenvironment,suggestingthatbehavingcollectivelymayconveyasignificantfitnessadvantagethroughfacilitatingfasterenvironmentalhabituation.Theseconddatachapterusedanindividual-basedapproachtoinvestigatetheeffectofindividualpersonalitytraits(intermsofboldnessandsociability)onthehabituationrateofindividualsoverconsecutivedays.Individualswereintroducedintoanovelenvironmenteachdayforthreeconsecutivedays.Theirsociabilitywasquantifiedbythetimethattheychosetospendincloseproximitytoavisibleshoalofconspecifics,andtherateatwhichtheyhabituatedtotheenvironmentoverthecourseofthetreedayswasmeasured.Thisstudyfoundnosignificantcorrelationbetweenanindividual’ssociabilityandthedegreetowhichtheyhabituatedtotheenvironment.However,thisstudydidprovideevidenceforboldnessbeingapersonalitytraitinsticklebacks.Therewasevidenceacrossbothofthestudiesthatsuggestedthatseveralindividualsdidnothabituatetotheirenvironmentstoasignificantdegreeoverthecourseofthetrials.Thismaybeduetosomelimitationsinthemethodsusedinthesetwostudies.Recommendationsforfurtherstudytopreventadesensitizationeffectfromoccurring(aswassuspectedinthisstudy)havebeendiscussed.

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DedicationandAcknowledgementsIwouldliketoparticularlythankmysupervisor,Dr.ChristosIoannou,forhissupport,guidanceandpatiencethroughoutthisresearchproject,andforkeepingmeontrack.ThankyoualsotoeverybodyfromtheUniversityofBristolinvolvedinthetrainingcourses,administrationanddeliveryoftheMastersbyResearchcourse.Thankyoutothelaboratorytechniciansforlookingafterthesticklebacks,andbeingsohelpfulandwelcomingtomewhenIfirststartedthecourse.ThanksalsotoAndrewSzopa-Comleyforhissupportduringthedatacollectionphaseoftheproject,andforhelpingtocatchthesticklebacks!AfinalthankyoutoTomClarksonandeverybodyatClarkson&WoodsEcologicalConsultantsLtd,whohavebeenincrediblysupportiveinthepastsixmonths,andforallowingmetimetowriteupthisthesis.

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AuthorsDeclaration

Ideclarethattheworkinthisdissertationwascarriedoutinaccordancewiththe

requirementsoftheUniversity'sRegulationsandCodeofPracticeforResearch

DegreeProgrammesandthatithasnotbeensubmittedforanyotheracademic

award.Exceptwhereindicatedbyspecificreferenceinthetext,theworkisthe

candidate'sownwork.Workdoneincollaborationwith,orwiththeassistanceof,

others,isindicatedassuch.Anyviewsexpressedinthedissertationarethoseofthe

author.

SIGNED:

DATE:

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TableofContentsTableofContents..................................................................................................5

Introduction...........................................................................................................7TheMechanismsofGroupBehaviour.......................................................................................................8PersonalandSocialinformation..................................................................................................................9Habituation........................................................................................................................................................11

DataChapter1:Investigatinginteractionsbetweenthecollectivebehaviourofgroupsandhabituationtoanovelenvironmentinsticklebacks(Gasterosteusaculeatus)

Introduction.........................................................................................................15

Methods...............................................................................................................19ExperimentalSubjects...................................................................................................................................19ExperimentalTank.........................................................................................................................................19ExperimentalProtocol..................................................................................................................................20DataAnalysis.....................................................................................................................................................20

Results..................................................................................................................25Theinteractionbetweencollectivenessandenvironmentalhabituation..............................27Discussion.............................................................................................................30Evidenceofconsensusdecisionmaking...............................................................................................30TheInteractionBetweenCollectiveBehaviourandEnvironmentalHabituation...............30

DataChapter2:Investigatingtheinteractionbetweensociabilityandenvironmentalhabituationinindividualsticklebacks(Gasterosteusaculeatus)

Introduction.........................................................................................................35

Methods...............................................................................................................40ExperimentalSubjects...................................................................................................................................40ExperimentalTank.........................................................................................................................................40ExperimentalProtocol..................................................................................................................................42Day1andDay3................................................................................................................................................42Day2......................................................................................................................................................................43

DataAnalysis.....................................................................................................................................................43Day1andDay3................................................................................................................................................43Day2......................................................................................................................................................................44MeasureofIndividualBoldness.................................................................................................................44

Results..................................................................................................................45Testingthekeyassumptionofhigherperceivedriskinopenareas.........................................45Wasanindividual’ssociabilityagoodpredictoroftheirdegreeofhabituation?...............45Evidenceofboldnessbeingapersonalitytraitinsticklebacks...................................................48

Discussion.............................................................................................................50TestingtheKeyAssumptionofOpenAreasBeingAssociatedWithaHigherPerceivedRiskofPredation.............................................................................................................................................50TheInteractionBetweenIndividualSociabilityandHabituation..............................................50Evidenceforboldnessasapersonalitytraitinsticklebacks........................................................53

Conclusion............................................................................................................55

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References............................................................................................................58

TableofFiguresFigure1:ExperimentalTankSetup..........................................................................................20Table1:Initialandtransformedvalueswhenthe'folding'transformationis

applied,toproducethe‘InitialCollectiveness’,‘EndCollectiveness’and‘WithinRefugeCollectiveness’terms.............................................................................23

Figure2:Histogramsshowingthedistributionsofthenumberoffishintheleftrefugewhenallindividualswereusingarefuge,foreachtrial..........................25

Figure3:Scatterplotshowingthecorrelationbetween‘initialcollectiveness’andthe‘withinrefugecollectiveness’ofeachgroup.......................................................26

Figure4:Scatterplotshowingtherelationshipbetweenagroup’scollectivenessatthestartofthetrialandthedegreetowhichgroupshabituatedtotheenvironment.............................................................................................................................28

Figure5:Boxplotcomparingthecollectivenessofallgroupsbetweenthebeginningandendofthetrials.........................................................................................29

Figure6:Stillimagestakenfromtrialvideos......................................................................42Figure7:Illustrationdetailingthesetupoftheexperimentaltankthroughoutthe

trials..............................................................................................................................................43Figure8:ThechangeintimespentoutsideoftherefugebetweenDay1andDay

3,relativetothesociabilityofeachindividualonDay2.......................................46Figure9:Boxplotshowingthevariationintheproportionofthetotaltrialtime

thatindividualsspentoutsideoftherefugesonDay1andDay3,andsocializingwiththeirconspecificsonDay2...............................................................47

Figure10:ScatterplotshowingthecorrelationbetweentheproportionoftimeindividualsspentoutsideoftherefugesonDay1andDay3..............................49

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IntroductionLivingingroupsisahugelywidespreadtrait,whichisfoundacrossmanyanimal

taxa.Wilson(1975)definedagroupas‘anysetoforganisms,belongingtothe

samespecies,thatremaintogetherforaperiodoftimeinteractingwithone

anothertoadistinctlygreaterdegreethanwithotherconspecifics’.Groupscan

belargelystableovertime–suchasprimategroups,wherethecompositionof

groupscanchangeverylittleoveranindividual’slifetime(Krauseetal.2014)–

orcanbevolatileandchangeinsizeandcompositionfromminutetominute.For

example,shoalingfishhavebeenfoundtoaltertheirgroupsizeinresponseto

dynamicenvironmentalcontexts,includingtheriskofpredationandavailability

offood(Hoareetal.2004).

Inorderfornaturalselectiontofavourtheevolutionofsocialbehaviour,thenet

fitnessbenefitsavailabletoanindividualremaininginagroupmustoutweigh

thefitnessbenefitsofanindividuallivingsolitarily.Therearemanyadvantages

anddisadvantagestogrouplivingthatarewelldocumentedintheliterature.An

advantageofgrouplivingisthatmembersofagroupmaybenefitfroman

increasedabilitytofindresourcessuchasfoodpatches(Pitcheretal.1982).This

isparticularlybeneficialwhenfoodexistsinbountiful,butscarcepatcheswithin

anenvironment,whichindividualsmaystruggletolocateindependently.

However,thesepotentialbenefitsareopposedbyanincreasedcompetitionfor

resourceswheninagroup,asafoodpatchmaynotholdenoughfoodforthe

entiregroup.Thiscanforcealargegrouptoincreasetheirforagingeffort,

spendingmoreenergyfindingfoodpatchesthansmallergroupsorsolitary

individuals(Janson1988).

Oneofthekeydriversofgroupbehaviouristhatindividualsingroups

experienceareducedriskofpredation(Lima&Dill1990)relativetosolitary

individualsinasimilarenvironment.Thisisachievedbyacombinationof

‘dilution’,‘detection’,and‘confusion’effects.Dilutioneffectsrefertothesharing

ofpredationriskacrossmembersofagroup,statisticallyreducingtheriskof

predationforeachindividualinthegroup(Foster&Treherne1981;Morgan&

Godin1985).

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Detectioneffects,alsoknownasthe‘many-eyes’effect,statesthatagrouphasa

higherlikelihoodofdetectingpredatorsthanasolitaryindividual,duetoa

highernumberofindividualsthatcanbevigilantforpredators(Elgar&Catterall

1981).Thishighersharedvigilanceallowsgroupedindividualstoreducetheir

ownvigilanceeffort(Quenette&Gerard1992;Roberts1996;Childress&Lung

2003),whichinturnenablesindividualstospendmoretimeexhibitingother

behaviours,suchasforaging(Lianetal.2007;Rieucau&Martin2008),without

sufferingfromanincreasedpredationriskasaresult.

Theconfusioneffectreferstothereductioninsuccessrateofpredatorattacks

thatcanbeattributedtothedifficultyoftrackingandattackingonetargetwhen

manytargetsareavailablesimultaneously(Ruxtonetal.2007).Theaccuracyof

predatorattackstendstoreducewithlargerpreygroupsizes,ashighnumbers

ofavailabletargetsinducepoorneuralmappingofpreylocationsbypredators

(Ioannouetal.2008).Thisreducesthepredationriskexperiencedbymembers

ofalargegroup.

TheMechanismsofGroupBehaviour

Manyspeciesacrossmultipletaxashowatendencytoformsocialgroups(Shaw

1978),suggestingthatthistraithasevolvedindependentlymanytimes,albeitto

varyingextents,acrosstheanimalkingdom.Itisclearthatbehavingsociallyhas

astrongevolutionaryfunction;byreducingtheriskofpredationofindividuals,

groupingcanprovidestrongpotentialfitnessbenefits.Althoughtheeffectsthat

providethisevolutionaryfunctionarerelativelycomplex,themechanismsthat

underpincollectivebehaviourarefairlysimple,andoccurlargelyatthelocal

level.

Individual-basedcomputermodelshavedemonstratedthatrealisticcollective

groupmovementcanbereproducedwhenafewsimplebehaviouralrulesdictate

thespatialpositioningofanindividualwithinagroup(Couzinetal.2002).

Firstly,individualsshouldavoidcollisionswithothergroupmembersby

maintainingasmallzoneofrepulsionbetweenthemselvesandneighbours.

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Secondly,individualsshouldbeattractedtowardsotherindividualsinorderto

remainpartofthegroup,andshouldalsotendtoaligntheirdirectionof

movementwiththeirneighbours(Couzinetal.2002).Whenindividualsfollow

thesesimplerulesatthelocallevel,highlycomplexcollectivebehaviouremerges

acrosstheentiregroup,suchasschoolingandshoaling.Thisphenomenonis

knownasself-organization,whereby‘patternsatthegloballevelemergesolely

frominteractionsamonglower-levelcomponents’(Camazineetal.2003).

Groupsoffishtendtospendthemajorityoftimeinoneofthreestablecollective

states–asapolarizedschool,atorus,orashoal(Pitcher&Parrish1993).Shoals

arediscrete,cohesivegroups,butarerelativelydisorderedattheindividual

level,asindividualsarenothighlyaligned(or,polarized)intheirdirectionof

movement.Individualsinaschooloratorusaligntheirdirectionofmovement

withtheirneighboursandarethereforepolarized;however,groupsinatorus

formationrotateaboutanemptycore(thusdisplayinglittletononetmovement

acrossaspace),whereasindividualsinaschooldoshownetmovementacross

space.Boththeoreticalmodels(Couzinetal.2002)andstudiesusingreal

subjects(goldenshiners,Notemigonuscrysoleucas)(Tunstrømetal.2013)have

demonstratedthatintermediatestatesbetweenthesethreeformationsare

relativelyunstable,andasaresult,groupstendtospendthemajorityoftimein

oneofthesethreestablestates.

PersonalandSocialinformation

Inordertofollowthesesimplelocalrules,anindividualmustconstantlymonitor

andprocessinformationregardingthebehaviourandmovementsofits

neighbours.Atanygiventime,anindividualwithinagroupisobtaining

information–bothprivatelyfromsensoryinformationaboutitsenvironment,

andsociallyfromothergroupmembers.Socialinformationcanbeacquiredin

twoways:throughsignals,wherebyinformationisintentionallytransferred

betweenindividualswithinagroup(i.e.analarmcall,alertingconspecificstoa

potentialattack);orthroughunintentionalcues,wherebythebehaviourof

otherscanunintentionallytransferinformationtoanindividual(Dalletal.

2005).Socialcuesthatmaybeusefultoanindividualinclude:theflightresponse

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ofotherconspecifics,revealingthelocationofapredatorattack;feedingby

conspecifics,revealingthelocationofafoodpatch(GalefandGiraldeau2001);

andmatingbehaviours,indicatingthepresenceofapotentialmateforthefocal

individual(Nordell&Valone1998).

Socialcuesalsoplayacriticalroleinsociallearning,particularlywithregardto

learningwhere,when,andwhat,toforage(GalefandGiraldeau2001).Thisis

demonstratedinstudiessuchasFryday&Greig-Smith(1994),wherebyred-

wingedblackbirds(Agelaiusphoeniceus)preferentiallyfedonthesamecoloured

foodastheywitnessedtheirconspecificsfeedingon.Inthisexample,observing

conspecificsfeedingonfoodofaparticularcolouractsasabehaviouralcue,

unintentionallytransmittinginformationfromthefeedingindividualtothe

observingindividual,regardingthepalatabilityoffoodofaparticularcolour.

Socialcuesarealsousedbyindividualstoacquireinformationaboutpredators,

andtolearncertainantipredatorbehaviours(Griffin2004).Forexample,

juvenileBelding’sgroundsquirrels(Spermophilusbeldingi)observingadults

respondtoanalarmcallaffectstherateatwhichtheythemselvesdevelopan

antipredatorresponsetoanalarmcall(Mateo&Holmes1997).

Beinginacoordinatedandcohesivegroupallowseachindividualtobenefitfrom

socialcuesandsignalstransmittedbyothermembersofthegroup(Couzinand

Krause2003;Wardetal.2008).Thistransferofsocialsignalsandcuesbetween

groupedindividualscanallowuninformedmembersofgroupstomakecorrect

decisions(thedecisionthatmaximisestheirfitness)approximatelyasoftenas

well-informedindividualsofthegroup(Magurran&Higham1988;King&

Cowlishaw2007).Forexample,often,onlyafewindividualsinashoalinitially

detectapredator,butthisinformationistransferredtootheruninformed

membersofthegroupbytheutilisationofsocialcues.Krause(1993)

demonstratedthatthiskindofinformationtransferoccursusingmixedshoalsof

chub(Leuciscuscephalus)andthree-spinedsticklebacks(Gasterosteusaculeatus).

Afterintroducingashoaltoanalarmsubstancethatchub,butnotsticklebacks,

aresensitiveto,Krausedemonstratedthatsticklebacksrespondtothepredator

avoidancebehaviourofthechubbyalsodisplayingpredatoravoidance

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behaviour.Thissuggeststhatthesticklebacksusedsocialcuesfromtheir

neighbours(thefrightresponseofthechubtothealarmsubstance)togather

informationabouttheirenvironment,andusedthisinformationtoinformtheir

decisiontoalsoexhibitantipredatorbehaviour.Furthermore,whengrouped

withchubthatwerehabituatedtothealarmsubstance(andthereforedidnot

produceafrightresponsetoit),thesticklebacksalsoproducednoresponse,

confirmingthatitwasthesocialcueproducedbythechub’sfrightresponseto

thesubstancethatwasguidingthestickleback’sbehaviour.

Whenobservingahighlycoordinatedgroupofanimals(e.g.astarling

murmurationoraschooloffish)reacttoapredatorattack,itisclearthatsocial

cues,intheformofpredatoravoidancebehaviour,aretransferredrapidly

betweenindividuals,spreadinginwavesthatpropagateincrediblyfastacross

theentiregroup(Hemelrijketal.2015).Sometimes,thespeedatwhichpredator

avoidancebehaviourspreadscanbefasterthanthespeedatwhichthepredator

attacksagroup(Treherne&Foster1981;Marrasetal.2012),resultingina

reducedpredatorsuccessrate(Procaccinietal.2011).Thisphenomenonis

knownastheTrafalgarEffect.

Informationcanbetransferredmoreefficientlywithinahighlypolarisedgroup

(Dayetal.2001),asanychangesintheorientationofneighbours(forexample,

inresponsetoapredator)canbedetectedmoreeasilywhenallindividualshave

similarorientations.Therefore,thetorusandschoolformationsbothallow

individualstoreceivethebenefitsassociatedwithahighdegreeofgroup

alignment.However,ifagroupiscohesive,butnotpolarised(i.e.moreofa

swarm/shoalformation,wheregroupmembersarenotalignedintheir

orientation),cuessuchaspredatoravoidancemanoeuvresaretransmittedless

efficiently(Couzinetal.2002).

Habituation

Whenanindividualfindsitselfinanovelorchangingenvironment,available

informationabouttheenvironment(i.e.thepresenceorlocationofpredators)is

minimal.WelkerandWelker(1958)demonstratedthatfishintroducedto

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noveltyinitiallyrespondbyretreating,andsuspendingtheiractivity(i.e.

freezing).Thisinitialbehaviouralresponseisknowngenerallyasa‘fright

response’.Thesebehaviouralresponsestonoveltysuggestthatindividualsmay

associatenovelenvironmentswithahigh-perceivedriskofpredation.

MillerandGerlai(2012)foundthatgroupsofzebrafish(Daniorerio)introduced

toanovelenvironmentinitiallytendedtobehaveverycollectively,forming

polarizedschools,butreducedtheirdegreeofcollectiveness(tendingtomore

oftenexistinshoals,ratherthanschools)followingseveralexposurestothe

environment,aswellasoverthedurationofasingleexposure.Thisinitialpeak

incollectivebehaviourfurthersuggeststhatindividualsassociatenovel

environmentswithahighpredationrisk,andrespondtothisbyexhibiting

antipredatorbehaviour-formingapolarizedschooloveralooseshoalinthese

high-risksituations.Schoolsmayreduceeachindividual’sriskofpredation,

relativetoalooseshoal,byconfusingapproachingpredatorstoagreaterdegree

(Bodeetal.2010;Ioannouetal.2012),andbyincreasingtheeaseof

transmissionofbehaviouralcues(suchassuddenchangesindirectionby

individualsinresponsetothelocationofapredator)betweenconspecifics,

potentiallyresultinginanincreasedabilitytoavoidpredators.Forthesereasons,

schoolingisconsideredanantipredatorbehaviour(Magurran1990).

However,asgroupsdonotindefinitelyexistinahighlypolarisedschool,itis

likelythattherearecostsassociatedwithbeingamemberofaschool.Schooling

maysimplybemoreenergeticallycostlythanshoaling.Forexample,studies

havefoundthatschoolstendtotravelfasterthanlessorganisedshoals(Parrish

etal.2002;MillerandGerlai2012).However,itisworthnotingthatthiseffectis

likelyaresultofshoalmembershavingunpolarizedorientationsandthus

travellingacrossspaceslowly,ratherthanpolarizedgroupsactivelyfavouring

fastertravelspeeds.

Theremayalsobeothercostsassociatedwithschooling,suchasareduced

potentialforindividualstoforagewhenpartofacoordinatedschool.Thiscould

occurasaresultofintensecompetitionbetweengroupmembersforfood

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resources,particularlyasthefieldofviewofanindividualwithinapolarised

groupislikelytooverlapwithmanyofitsneighbours’fieldsofview(Eggers

1976).Giventhatfoodpatchesareoftenonlyavailableforalimitedperiodof

time,itmaybemorebeneficialundercertaincircumstancestoindependently

forage,becauseafoodpatchmaybedepletedbythetimetheentiregroup(and

thussomeindividualswithinagroup)reachesthefoodpatch.Therefore,an

individualmayobtainagreaterenergeticbenefitfromafoodsourceifitis

discoveredindependentlyfromagroup(Dechaume-Moncharmontetal.2005).

Thisindicatesthatthereisatrade-offassociatedwithbeingamemberofa

polarisedgroup.Groupmembersmayreducetheirriskofpredation,but

potentiallyatanenergeticcost,throughthelossofforagingopportunities.

Asaresult,itisoptimalforindividualstoonlyformpolarisedschoolswhenthe

perceivedriskofpredationishigh.Whentheperceivedpredationriskislow(for

example,followinghabituationtoanovelenvironment),thecostsofschooling

mayoutweightherequirementforantipredatorbehaviour;thereforeindividuals

mayobtainthegreatestbenefittofitnessbyreducingtheircollectiveness,and

exploringorforagingalone,orinalesspolarisedgroup.Theprocessofbecoming

accustomedtoanovelenvironment,andtheequalisationoftheperceivedrisk

andactualriskoftheenvironmentisreferredtointhisstudy,andothers(Miller

andGerlai2012),asenvironmentalhabituation.Notethatthedefinitionusedin

thisstudyslightlydifferstotheclassicaldefinitionofhabituation,wherebythe

responseofanindividualtoanon-threateningstimulusreducesoverrepeated

exposures.Inthisstudy,environmentalhabituationisessentiallythereduction

ofantipredatorbehaviourasanindividualbecomesaccustomedtoanovel

environmentovertime,asthereisnoactualriskofpredationinthe

experimentalsetups.

Environmentalhabituationisexpectedtooccuronceanindividualhasmadean

accurateassessmentofthepredationriskofaparticularenvironment.Ifan

individual’sperceivedriskofpredationishigherthantheactualpredationriskof

agivenenvironmentforaprolongedperiod,individualsmaywastetimeand

energyinvestinginantipredatorbehaviours(suchasusingrefugesorschooling

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withconspecifics),whentheycouldbeexhibitingotherbehavioursthatbenefit

fitness,suchasforaging.Thus,habituatingtoanovelenvironmentasquicklyas

possiblemayhaveanimportantpotentialbenefittoanindividual’sfitness.This

isdemonstratedinRodriguez-Prietoetal.(2010a),whereIberianwalllizards

(Podarcishispanica)thathabituatedfastertoafrequentlyencounteredlow-risk

predatorhadbetterbodyconditionthanindividualswhohabituatedtothe

predatortoalesserextent.

Ifthesharingofsocialinformationbetweengroupmemberscanincreasean

individual’srateofenvironmentalhabituation,thismayprovideindividualswho

behavecollectivelyafitnessbenefitbyoptimizingtheirenergyusage.Ifthiswere

thecase,thiswouldsuggestthatinformationtransfermayhaveanimportant

roleinincreasingthefitnessofcollectiveindividuals,andthusmayalsobea

driveroftheevolutionofsocialbehaviour.

Thisthesisaimstoinvestigatetheinteractionsbetweencollectivebehaviourand

environmentalhabituation.Thefirstdatachapterisagroup-basedstudywhich

investigatestherateatwhichgroupsofvaryingcollectivenesshabituatetoa

novelenvironment,inordertoassesswhethermoreefficientinformation

transferbetweenmorecollectivegroupscanfacilitateafasterrateof

environmentalhabituation.Theseconddatachapterusesanindividual-based

approachtoinvestigatetheeffectofindividualpersonalitytraits(intermsof

boldnessandsociability)onthehabituationrateofindividualsoverconsecutive

days.

Bothofthedatachapterswithinthisthesisuseagroup’scohesiveness(thatis,

thetendencyforindividualsinagrouptoremaincloselyassociatedwitheach

otherinspace)asameasureoftheircollectiveness.Grouppolarisation(thatis,

thetendencyforindividualsinagrouptoaligntheirdirectionoftravelwitheach

other)wasnotmeasuredinthesestudies.Thereforewhenreferringtogroups’

collectivenesswithinthisthesis,thisonlyreferstogroupcohesion.For

simplicity,groupcohesivenesswillbereferredtothroughoutthisthesisas

‘collectiveness.’

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DataChapter1:Investigatinginteractionsbetweenthecollectivebehaviourofgroupsandhabituationtoanovelenvironmentinsticklebacks(Gasterosteusaculeatus)

Introduction

Thereareseveralantipredatorbenefitsassociatedwithbeingamemberofa

group,ashasbeenpreviouslydiscussed(Elgar&Catterall1981;Foster&

Treherne1981;Morgan&Godin1985;Lima&Dill1990;Ruxtonetal.2007;

Ioannouetal.2008).Inordertoremainpartofacohesiveandcoordinated

group,individualsmustsynchronisetheirdecisionmakingwiththatofother

groupmembers.However,ifindividualsblindlyfollowthedecisionsofother

groupmembers,thiscanleadtoaninformationalcascade,andresultinapoor

decisionbeingtakenbyallmembersofagroup(Dalletal.2005).Ifindividuals

neverbiastheirdecision-makingtowardthatofothergroupmembers(i.e.only

makedecisionsbasedonprivateinformation),theyfailtoexploitthepotential

fitnessbenefitsavailablefromeffectivelyutilisingsocialinformation,andthe

groupmayundergofission.

Therehavebeenanumberofmechanismsproposedtoexplainhowindividuals

withinagrouputilisepersonalandsocialinformation,andcometoadecision

thatmaximisestheirfitness.Themechanismsthatunderlieconsensusdecision-

makingcanvarybetweenspeciesandcontexts.Forexample,groupsmaymake

‘unshared’decisionstocometoaconsensus,throughmechanismssuchas

despotism(whereindividualscopythedecisionsofleaders)(Conradt&Roper

2003).Ontheotherhand,groupsmaymake‘shared’decisions,wherebyall

individualscontributetothedecision(forareviewseeConradt&Roper2005;

King&Cowlishaw2009).Severalstudieshaveshownthatingroupsoffish(and

manyotherorganismsthatformgroups),aformofshareddecisionmaking

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tendstooccur,knownasquorum-decisionmaking.Thisisasimplerule,

wherebyanindividual’stendencytomakeaparticularbehaviouraldecision

increaseswiththeproportionofotherconspecificswhohavemadethesame

decision(Wardetal.2008).

Whenmakingamovement-baseddecision,usingquorumdecision-making

allowsgroupstocometoaconsensus,andpreventsthegroupfromsplitting.

ThisisseeninHalloyetal.(2007),wherecockroachestendedtoreacha

consensuswhenchoosingwhichoftworefugestoshelterunder,thereby

preventingthefissionofthegroupbetweentworefuges.Furthermore,Halloyet

al.(2007)andothers(Wardetal.2008)havedemonstratedthatthisdecision

makingprocesscanbemanipulatedbythe‘decisions’ofman-madereplica

conspecificsthatarecontrolledbytheresearcher,providinganeffectivemethod

ofstudyingtheseaspectsofcollectivedecisionmakinginthefuture.Thisstudy

willinvestigatewhethergroupsofsticklebacksshowevidenceofconsensus

decisionmakingwhentraversingthenovelenvironment,byexaminingwhether

groupstendtoallutiliseonerefugeatthesametime,orwhethertheyshowno

preferenceforcomingtoaconsensus,andtendtoutilisetwoseparaterefugesat

thesametime.

Usingarefugemaybenefitanindividualbyreducingtheirimmediateriskof

predation(Cowlishaw1997;Sih1997);however,therearealsocostsassociated

withusingrefuges.Individualsmayloseoutonfeedingopportunitiesasaresult

ofspendingtimewithinarefuge,ratherthanforaging(Krauseetal.1998).

Therefore,ifanindividualspendsaprolongedperiodoftimewithinarefuge

whentheactualpredationriskislow(andtherefore,thedefenceprovidedbya

refugeisnotrequired),thatindividualsuffersapotentialcosttofitness,through

thelossoffeedingopportunities.Thissuggeststhatanindividualshouldonlyuse

arefugewhenthereisahighriskofpredation,inordertooffsetthecostsof

usingarefugewiththeantipredatorbenefitsthattheyprovideinhigh-risk

situations.Asanindividual’sdecisiontousearefugeatanygiventimetendsto

reflectitsperceivedriskofpredationwithinanenvironment,manystudieshave

usedrefugeuseasaproxytoestimateanindividual’sperceivedriskofpredation

17

(Krauseetal.1998;Martin&Lopez2005),orhaveassumedthatleavingarefuge

isanactionthatanindividualperceivesashigh-risk(McDonaldetal.2016).This

studyalsousestheassumptionthatanindividual’stendencytousearefuge

reflectsitsperceivedlevelofpredationriskatanygiventime.Forexample,asan

individualhabituatestothetestenvironmentovertime,itsperceivedriskof

predationwilldecrease,andasaresult,wewouldalsoexpectitstendencyto

occupyarefugetoalsodecrease.Thischangeinrefugeuseformsthe

quantitativemeasureofagroup’srateofhabituationinthisstudy.

In1999,LimaandBednekoffcreatedthePredationRiskAllocationHypothesis

(Lima&Bednekoff1999,forareviewsee:Beauchamp&Ruxton2011).This

modelrecognisesthattheriskofpredationinanenvironmentvariestemporally

andspatially.Thiscanbeduetoseveralfactors,suchastheactivitypatternsof

predators(FennandMacdonald1995),thedistancetonearbyrefugia,andthe

sizeofthegroupofprey(Creel&Winnie2005).ThePredationRiskAllocation

Hypothesisstatesthatinordertomaximisetheirfitnesswhilstalsomeeting

theirenergydemands,individualsinhighrisksituationsshouldexhibitstrong

antipredatorbehaviours,andallocatelesstimetoforaging;whereasinsituations

withalowriskofpredation,individualsshouldallocatemoreefforttoforaging,

andlesstoantipredatorbehaviours.Thismodelshouldalsoapplytosituations

wheretheperceivedriskofpredationishighorlow,regardlessofwhetherthere

isarealthreatofpredationornot(forexample,inanovelenvironmentwhere

thepresence/absenceofpredatorshasnotbeenestablished).

ByadaptingthepredictionsofthePredationRiskAllocationHypothesistothis

experiment,wecanreachourhypothesisforthisstudy:atthebeginningofthe

trials(whentheperceivedpredationriskisatitshighestandgroupsarenot

habituatedtothenovelenvironment),theexhibitionofantipredatorbehaviour

shouldbeatitspeak,asthegroupholdslittletonoinformationregardingthe

predationriskofthenovelenvironment.Inthecontextofthebehaviours

measuredinthisstudy,thiswillfacilitateasgroupsmovingaroundthenovel

environmenthighlycollectivelyandexhibitingahighlevelofrefugeuse.

However,asthegroupshabituatetotheenvironmentoverthecourseofthetrial,

18

wehypothesisethatindividualswillreducetheirexpressionofantipredator

behaviours,resultinginareductioninoverallcollectivenessandlessfrequent

refugeuse.AlthoughthePredatorRiskAllocationHypothesispredictsthat

individualsshouldforagemorefrequentlyinlowrisksituations,theforaging

rateofindividualswillnotbemeasuredinthisstudy,astherewillbeno

availablefoodresourcesintheexperimentalsetup.

Ascollectivebehaviourfacilitatesthetransferofsocialinformationbetween

groupmembers,oursecondhypothesisisthatgroupsthatbehavemore

collectivelyatthebeginningofthetrialswillhabituatetotheirenvironment

fasterthanlesscollectivegroups,duetotheadvantagethatsharingsocial

informationprovidestogroupsthatbehavecollectively.

19

Methods

ExperimentalSubjects

Three-spinedsticklebacks(Gasterosteusaculeatus)werecaughtfromtheRiver

CaryinSomersetbetweenSeptemberandNovember2016.Thesubjectswere

heldin90Ltanks(70cmx40cmx35cm)inatemperature-controlledroom

(watertemperaturewas15-17degreescentigrade),withcontrolleddaily

photoperiodsof12hours.Thepopulationwerefedamixofbloodworm(Glycera

sp.),andcrustaceans(Mysissp.andArtemiasp.)oncedailyinthemorning,before

thetrialstookplace.Thisexperimentused160individualsfromalargerwild-

caughtpopulation.

ExperimentalTank

Theexperimentalsetupconsistedofanarrowtrialarea(70cmlengthx20cm

width)withinalargertank(90L,70cmx40cmx35cm)forthetrialtotakeplace

(seeFigure1).Thetrialareawasbuiltbyfixingafalsewallwithinthetank,

paralleltothelongestsideofthetank,creatinganarrowareaatthefrontofthe

tank.Thetrialswerefilmedfromthefrontofthetank,usingaPanasonicHC-

X920videocamera(1080p,50fps).Withinthetrialarea,therewasanidentical

refugeoneitherend(18cmdeep,10cmhigh,20cmwide)madefromblack

plasticmesh,andanopenarea(length32cm)betweenthetworefuges.These

refugeswerestaple-shaped,withmeshcoveringbothofthesidesandthetop.

Thebackoftherefugewasformedbythesidewallofthetank,andthefrontof

therefugewasleftopentofacilitatethefreemovementoffishbetweenthe

refugesandtheopenarea.Thisformedtwoshadedareasinthetank,whichwere

consideredtoofferareasofrefugeforthefish.Studieshaveshownthatfish

utiliseshadedareasasrefugesfrompredation(Helfman1981;McCarttetal.

1997),andshadedareashavebeenassumedtoactasrefugesinseveralother

studies(Reebs2000;Sumpteretal.2008).

Atthebeginningofatrial,apartitionmadefromopaquePerspexwasfixedin

placeatthemidpointoftheopenarea(whichwasmarkedusingpermanent

markerpenontheoutsideoftheglass)usingsmallmagnets.Thisbarrierwas

20

removedfollowinganacclimatisationperiodof150secondsafterthefishwere

introducedtothetank.

Figure1:ExperimentalTankSetup.Inthisphoto,thePerspexbarrierisinplaceinthe

centreofthetank.

ExperimentalProtocolGroupsofeightrandomlyselectedindividualsweretestedineachtrial.The

groupwereintroducedtoarandomlyselectedsideofthetrialarea(whichwas

selectedusingarandomnumbergenerator),andlefttoacclimatizefor150

secondsbeforethecentralpartitionwasremoved,andthetrialbegan.Eachtrial

lasted30minutes,duringwhichtimethesubjectswerelefttofreelymove

betweenthetworefuges,andaroundtheopentrialarea.Twentytrialswere

conductedintotal.

DataAnalysis

Thestatisticaltestsconductedwithinthisdatachapteruseasymptoticp-values

unlessotherwisestated.

ThetrialvideoswereanalysedusingBehaviouralObservationResearch

InteractiveSoftware(BORIS).Thisisasoftwareprogrammethatallowstheuser

towatchatrialvideo,andrecordeachoccurrencethatthefocalindividualsin

thevideoexhibitspecificbehavioursofinterest.Thisallowstheusertoanalyse

videofootageinrealtime,andproducequantitativedataofthebehaviours

observedduringthevideo.Thisdatacanthenbedownloadedintheformofa

spreadsheet,andthenanalysedusingstatisticalsoftware.

21

Twosetsof‘behaviours’wererecordedusingtheBORISprogramme.Thefirst

wasthenumberoffishoutsideoftherefuges(i.e.withintheopenarea)atany

giventime.Thisvariablehadaminimumvalueof0andamaximumvalueof8.

Eachtrialwasobservedinrealtime,andthenumberoffishthatcouldbe

observedoutsideoftherefugeswascontinuouslyrecorded,withanychangesin

thenumberoffishoutsideoftherefugesrecordedbypressingthecorresponding

numberonthekeyboard.

Thesecondvariablerecordedwasthenumberoffishineachofthetworefuges,

whenalleightindividualswerewithintherefuges(i.e.whennoneofthefish

wereintheopenareaofthetank).Inordertocreatethisvariable,thetrial

videoswereviewedinrealtimeasecondtime,andeachtimealleight

individualswerewithintherefuges,thevideowaspaused,andthenumberof

individualswithintheleftrefugewascountedandrecordedbypressingthe

correspondingnumberonthekeyboard.Thisvariablemadeitpossibleto

determinewhethergroupstendedtoreachaconsensus,wherebyallindividuals

wouldoccupythesamerefuge,orwhethergroupstendedtosplitbetweenthe

tworefuges.Collectiverefugeusewouldmanifestasextremevaluesofthis

variable(0or8individualsintheleftrefuge,dependingonwhetherall

individualswereusingtherightorleftrefuge,respectively).Weaklycollective

refugeusewouldmanifestasvaluesinthemiddleoftherangeofthevariable

(around4individualsineachrefuge),suggestingthatindividualsdonothavea

strongpreferenceforusingrefugescollectivelywiththerestofthegroup.

Asremovingthecentralpartitionmayhavecausedafrightresponseinthefish,

influencingthemovementandbehaviourofindividualsatthestartofeachtrial,

thefirstfiveminutesofeachtrialwasdiscountedfromanyanalysis.Thiskindof

omissionwasalsoconductedinIoannouetal.(2017),inordertoremovethe

influenceoffrightresponsesontheanalysisoftherestofthetrialdata.

DegreeofHabituation

UsingthedataacquiredfromtheBORISsoftware,themeannumberoffish

outsideoftherefugeswascalculatedforthefiveminutesatthestartofeachtrial

22

(05:00-10:00,asthefirstfiveminuteswasomittedfromallanalyses),andthe

finalfiveminutesofeachtrial(25:00-30:00)foreachgroup.

Inordertoassessthedegreetowhichagrouphabituatedtothenovel

environmentoverthetrialperiod,themeannumberoffishoutsideofthe

refugesbetween05:00-10:00miniuteswassubtractedfromthemeannumberof

fishoutsideoftherefugesbetween25:00-30:00minutes.Thismeasureallowed

ustoexaminethechangeineachgroup’sexplorationoftheopenareaoverthe

trialperiod,andthusprovidesaquantitativemeasureforthedegreeof

habituationexhibitedbyeachgroup.Ifhabituationhadoccurredthroughthe

trial,wewouldexpectanincreaseinboldnessbetweenthestartandtheendof

thetrial,wherebyindividualsshowagreatertendencytooccupytheopenarea

ofthetank(whichislikelyperceivedtocarryahigherriskofpredationthanthe

refuges)asthetrialsprogressed.Thiswouldmanifestitselfasahigh‘degreeof

habituation’value.

InitialCollectivenessandEndCollectiveness

Threemeasuresofcollectivenesswerecalculatedforeachtrial.Thefirst,‘Initial

Collectiveness’,wasproducedtoassesshowcollectivelyeachgrouputilisedthe

refugesandtheopenareabetween05:00and10:00,relativetoallothergroups

thatwereobserved.

Thenumberoffishoutsideoftherefugesatanygiventimebetween05:00and

10:00wastransformedseveraltimesinordertoproducearelativemeasureof

collectiveness.First,thedatawasfolded,sothatallvalueslaybetween0and4,

ratherthan0and8(seeTablexfordetails).Beforethistransformation,acount

of0wouldindicatethatalleightindividualswerewithintherefugesatthatgiven

time,whereasacountof8wouldindicatethatalleightindividualswerewithin

theopenareabetweenthetworefugesatthatgiventime.Asbothofthese

situationsindicateahighdegreeofgroupcohesion,thisfoldingtransformation

removedthedifferencebetweenthesevalues.Thisresultedinascalebetween0

and4,wherebycountsindicatingahighdegreeofgroupcohesionwereallgiven

23

avalueof0,andhighercountsindicatedthatthegroupwassplitbetweenthe

refugesandtheopenspace.

Themeanofthesevalueswastakenandthensubtractedfrom4toreversethe

valuessothatahighermeanvaluewouldindicatestronger,ratherthanweaker,

collectiveness,andthesevaluesforeachtrialwerethennormalisedtorange

from0to1.Thismeasureofcollectivenesswasusedtodeterminewhethera

group’srateofhabituationtoanovelenvironmentcouldbepredictedbyhow

collectivelythegroupbehaveswhenfirstintroducedtothenewenvironment.

Themethodthatwasusedtoproducetheinitialcollectivenessmeasurewas

repeatedonthedatainthefinalfiveminutesofeachtrial(25:00–30:00)in

ordertoproducetheterm‘endcollectiveness’.Thistermwasproducedinorder

toassesswhethergroupcollectivenessincreasedordecreasedoverthecourseof

eachtrial.

Table1:Initialandtransformedvalueswhenthe'folding'transformationisapplied,to

producethe‘InitialCollectiveness’,‘EndCollectiveness’and‘WithinRefugeCollectiveness’terms.Theinitialvaluerepresentsthenumberoffishoutsideoftherefugesatanytimeduringtheperiodofinterest(05:00-10:00forinitialcollectivenessand25:00-30:00forendcollectiveness).Valuesthatchangeaftertransformationarehighlighted.Formulafor

‘folding’transformation:Ifx1>4,x2=abs(x1-8)

InitialValue(x1) ‘Folded’TransformedValue(x2)

0 0

1 1

2 2

3 3

4 4

5 3

6 2

7 1

8 0

WithinRefugeCollectiveness

Thethirdmeasureofcollectivenesswascalculatedfrom05:00-30:00ofthetrial

(duetotheomissionofthefirstfiveminutesofthetrialfromallanalyses).

24

Whenalleightindividualswerewithineitheroftherefuges,thenumberoffish

intheleftrefugewascounted.Thesecountswerethenfolded,usingthesame

methodologyasthatusedinTable1.Eachoccurrenceofalleightindividuals

utilisingtherefugesatthesametimewasgivenaweight,basedontheduration

thatallindividualsremainedwithintherefuges.Theweightedmeannumberof

fishinsidetheleftrefugewhenallindividualswereutilisingtherefugeswasthen

calculatedforeachtrial.Theseweightedmeanswerethenflippedand

normalisedusingthesameprocessasin‘InitialCollectiveness’.These

transformationsproducedatermthatindicatedhowcollectivelyeachgroup

usedtherefugesthroughoutthetrial,wherebyalower‘withinrefuge

collectiveness’valueindicatedthatthegroupwereweaklycollectivewhenusing

therefuges(i.e.thegroupwasoftensplitbetweenthetworefuges),andahigher

valueindicatesthatthegroupbehavedverycollectivelywhenusingtherefuges

(i.e.alleightindividualstendedtousethesamerefugeatthesametime).

25

ResultsFigure2showsthedistributionofthenumberofindividualsintheleftrefuge

duringeachoccurrenceofwhenallfishwereusingarefuge,foreachtrial.The

distributionswerelargelyeitherunimodal(withapeakateitherx=0orx=8),or

bimodal(withpeaksatx=0andx=8)acrossgroups.Thissuggeststhatgroups

tendedtocometoaconsensusregardingwhichoftheidenticalrefugestouse,

withallindividualstendingtousethesamerefugeatthesametime.

Figure2:Histogramsshowingthedistributionsofthenumberoffishintheleftrefuge

whenallindividualswereusingarefuge,foreachtrial.Notethatwhenx=0,allindividualswereusingtherightrefuge,andwhenx=8,allindividualswereusingtheleftrefuge.

ASpearman’srankcorrelationtestwasconductedonour‘initialcollectiveness’

and‘withinrefugecollectiveness’measures.Thetwomeasureswerepositively

correlatedwithstatisticalsignificance(n=20,rs=0.547,p=0.013,seeFigure3

below).Thisindicatesthatgroupsthatshowedagreatertendencytomove

aroundthenovelenvironmentasacohesivegroupduringthefirstfiveminutes

ofthetrialalsotendedtousetherefugesmorecollectivelythroughoutthe

durationofthetrial,relativetogroupsthatinitiallywerelesscohesive.Thatisto

say,thatthoseindividualswithingroupsthathadahigher‘initialcollectiveness’

26

valuechosetohideunderthesamerefugeastheirconspecificsmoreoftenthan

groupsthatinitiallybehavedlesscollectively,andthusremainedamore

cohesivegroupthroughoutthetrials.

Thefactthattherewasasignificantcorrelationbetweenthesetwomeasuresof

collectivenessalsosuggeststhattherewasadegreeofvariabilitybetween

groupsinhowcollectivelytheybehavedinthetrials.Thisisimportant,as

withoutanyvariabilityincollectivenessbetweenthetrialgroups,itwouldbe

impossibletomakeinferenceswithregardtotheinteractionsbetweenhow

collectivelyagroupbehavesandthedegreetowhichtheyhabituatetothenovel

environmentoverthecourseofatrial.

Figure3:Scatterplotshowingthecorrelationbetween‘initialcollectiveness’(collectivenesswithintheinitialfiveminutesofthetrial)andthe‘withinrefugecollectiveness’(tendencyofindividualswithinagrouptocometoaconsensuswhenchoosingarefuge)ofeachgroup.

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

Initial Collectiveness

With

in R

efug

e C

olle

ctiv

enes

s

27

Theinteractionbetweencollectivenessandenvironmentalhabituation

Theinitialcollectivenessofeachgroupwasfoundtobepositivelycorrelated

(Spearman’srank:n=20,rs=0.474,p=0.036)withthedegreeofhabituation

(thatis,thechangeinthemeannumberoffishoutsideoftherefugesbetween

theinitialfiveminutesandfinalfiveminutesofeachtrial,or,thechangein

explorationofthe‘risky’openareaasthetrialprogressed)ofeachgroup.This

suggeststhatgroupsthatbehavedmorecollectivelynearthestartofeachtrial

habituatedtothetestenvironmenttoasignificantlygreaterdegreethanless

collectivegroups.Thishabituationwasexpressedasagreaterincreaseinthe

meannumberoffishexploringtheopenareaasthetrialprogressedingroups

thatbehavedmorecollectively.

However,itappearsthatmanygroupsdidnothabituatetotheenvironmentover

thecourseofthetrials(seeFigure4).Sevengroupsshowedsignsofhabituation,

expressinganincreaseintimespentexploringthe‘risky’openareaasthetrials

progressed,howevertheremainingthirteengroupsexhibitedareductioninthe

meannumberoffishexploringtheopenareabetweenthebeginningandendof

thetrials(Figure4).Thisreductionistheoppositeofwhatwouldbeexpectedif

agrouphadhabituatedoverthecourseofthetrial,asonewouldexpectagroup

tospendmoretimeinthe‘risky’openareaastheyhabituatedtothe

environmentoverthecourseofthetrial.Acrossallgroups,therewasfoundtobe

nosignificantdifferencebetweenthemeannumberoffishoutsideoftherefuges

atthebeginning(05:00-10:00)andend(25:00-30:00)ofeachtrial(Wilcoxon

signedranktest:n=20,V=60,p=0.097).However,asthisresultisonly

marginallyabovethesignificancethreshold(asp>0.05),thissuggeststhata

differencebetweenthesevariablesmaystillbepresent.

28

Figure4:Scatterplotshowingtherelationshipbetweenagroup’scollectivenessatthestartofthetrialandthedegreetowhichgroupshabituatedtotheenvironment.Positiveyvaluesindicatethatthegroupshowedsignsofhabituationoverthecourseofthetrial(i.e.thattherewasapositivedifferencebetweenthemeannumberoffishoutsideoftherefugesbetweenthebeginningandendofthetrial).

Similarly,therewasnosignificantdifferencebetweenthecollectivenessof

groupsatthestart(initialcollectiveness)andend(endcollectiveness)ofthe

trials(Wilcoxonsignedranktest:n=20,V=78,p=0.33),althoughthemedian

collectivenesswasslightlylowerattheendofthetrialsthanatthestartofthe

trials(Figure5).Thissuggeststhatgroupsdidnotsignificantlyreducehow

collectivelytheybehavedasthetrialsprogressed.

0.0 0.2 0.4 0.6 0.8 1.0

-0.6

-0.4

-0.2

0.0

0.2

Initial Collectiveness

Deg

ree

of H

abitu

atio

n

29

Figure5:Boxplotcomparingthecollectivenessofallgroupsbetweenthebeginningandendofthetrials.

The‘withinrefugecollectiveness’measurewasnotsignificantlycorrelatedwith

thehabituationrateofeachgroup(rs=0.354,p=0.126),ortheboldnessofeach

group(rs=-0.226,p=0.339).Thissuggeststhatthedegreetowhichgroups

cametoaconsensuswhenutilisingtherefugeswasnotagoodindicatoroftheir

rateofhabituation,ortheirtendencytospendtimeexploringthe‘risky’open

areaofthetank.

Initial 5 minutes End 5 minutes

0.0

0.2

0.4

0.6

0.8

1.0

Collectiveness

30

Discussion

EvidenceofconsensusdecisionmakingTheclearuni-modalandbi-modaldistributionsofthenumberofindividuals

withintheleftrefugewhenallindividualswereutilisingtherefuges(seeFigure

2)suggeststhatmostgroupstendedtocometoaconsensusdecisionwhen

choosingwhichofthetworefugestoenter.Reachingaconsensusdecisionon

whichrefugetousepreventsagroupfromsplittingbetweenthetworefuges.

Groupfissionmayreducetheantipredatoradvantagesassociatedwithbeinga

memberofagroupforallindividuals,aseffectsthatreduceindividuals’

predationrisksuchasthedilution,detectionandconfusioneffectsareallless

effectiveinsmallergroups(Roberts1996;Ioannouetal.2008).Studieshavealso

shownthatlargergroupstendtomakemoreaccuratedecisionsmoreoftenthan

smallergroups(Sumpteretal.2008),soitfollowsthatagroupmaymakemore

accuratedecisions(thedecisionthatbenefitsindividuals’fitness),andreduce

theirriskofpredationmoreeffectivelyifitsmemberscanreachaconsensusand

avoidundergoingfissionwhenmovingaroundanenvironment.

Althoughthisstudyprovidesevidenceforconsensusdecision-makingin

sticklebacks,themechanismdrivingthisconsensusdecision-making(thatis,

whetherindividualsreachedaconsensusthroughfollowingaquorumresponse

rule,whetherthedecisionisunsharedandindividualsfollowparticularleaders,

orgroupsfollowsomeothermechanismtoreachaconsensus)isoutsideofthe

scopeofthisstudy.However,previousstudieshavedemonstratedthatthe

movement-baseddecisionsoffishareconsistentwiththatofaquorumresponse

(Wardetal.2008).Therefore,itislikelythatthisisthemechanismthatdrove

individuals’selectionofrefugiawithinthisstudy.

TheInteractionBetweenCollectiveBehaviourandEnvironmentalHabituationThewithinrefugecollectivenessmeasure(howcohesivethegroupremained

whenallindividualswereutilisingtherefuges,wherebygroupsthatcametoa

consensusandallchosetoutilisethesamerefugeweregivenahigh‘within

refugecollectiveness’value)wasfoundtobepositivelycorrelatedwiththeinitial

31

collectivenessmeasure(thegroupscohesionwhenutilisingboththerefugesand

theopenarea),whichsuggeststhatbothweremeasuringsimilaraspectsof

behaviour(i.e.howcollectivelyagroupwasbehaving).Inthiscontext,theseare

howcollectivelyagroupbehavedatthebeginningofatrial,andhowcollectively

thesamegroupbehavedwhenusingtherefugesthroughoutthetrial.

Thepositivecorrelationbetweenhowcollectivelyagroupbehavedatthe

beginningofthetrial(whichwasbasedonthenumberofindividualsoutsideof

therefugesatanygiventimewithintheinitialfiveminutesofthetrial)andthe

degreetowhichtheyhabituatedtothenovelenvironment(whichwasbasedon

themeandifferenceinindividualsoutsideoftherefugebetweentheinitialand

finalfiveminutesofthetrial)suggeststhatbehavingcollectivelydoesoffer

potentialbenefitstoagroup’srateofhabituation.Anindividual’srateof

habituationcanhavefitnessconsequences(Rodriguez-Prietoetal.2010a),

becauseifanindividual’sperceivedriskofpredationishigherthantheactual

predationriskofagivenenvironmentforaprolongedperiod,individualsmay

wastetimeandenergyinvestinginantipredatorbehaviours(suchasusing

refugesorschoolingwithconspecifics),whentheycouldbeexhibitingother

behavioursthatbenefitfitness,suchasforaging.Thisindicatesthatbehaving

collectively(and,consequently,sharingsocialinformationwithothergroup

members)canoffersignificantfitnessadvantages,otherthanthatobtainedfrom

directlyreducingindividuals’predationriskthroughdetection,dilutionand

confusioneffects(Elgar&Catterall1981;Lima&Dill1990;Ruxtonetal.2007;

Ioannouetal.2008),andthereforeinformationtransfermaybeadriverofthe

evolutionofcollectivebehaviour.

However,althoughtherewasconsiderablevariationinhowcollectivelyeach

groupbehaved,therewasfoundtobenosignificantdifferenceinthetimethat

groupsspentoutsideoftherefugebetweenthestartandendofeachtrial.Many

groupsinthestudydidnotexhibitanincreaseinthetimespentintheopenarea

overthecourseofthetrials,andthereforeshowednosignsofenvironmental

habituation.Thiscouldhaveoccurredforanumberofreasons.Firstly,the

durationofthetrials(30minutes,excludingtheacclimatisationperiodof2:30at

32

thebeginningofatrial,beforethepartitionwasremoved)mayhavebeen

insufficientforgroupstohabituatetotheenvironment.Otherstudiessuchas

MillerandGerlai(2012)havedemonstratedasignificanthabituationeffectin

trialsofthirtyminutes,however,focalindividualsweretrialedforthirtyminutes

dailyoveraseriesoffivedays,sotheoveralldurationspentwithinthenovel

environmentismuchhigherinMillerandGerlai(2012)thanthatusedinthis

study.McDonaldetal.(2016)alsoobservedahabituationeffectwhentrialling

groupsovertwotwenty-minutetrialsacrosstwoconsecutivedays,whichagain

resultsinalongerdurationthatindividualsareexposedtothenovel

environmentthantheindividualsusedinthisstudy.Perhapsifthetrialsinthis

studywerelonger,highlycollectivegroupsmayhaveshowedagreaterdegreeof

habituation,demonstratingagreaterpotentialbenefittoenvironmental

habituationfrombehavingcollectively.However,itispossiblethatallgroups

mayhaveexhibitedahigherdegreeofhabituationifthetrialswerelonger,

obscuringthepotentialbenefitofbehavingcollectivelyontherateof

environmentalhabituation.

Anotherpotentialexplanationforthelackofhabituationexhibitedbysome

groupsisthattherewasnoincentiveforgroupstoextensivelyexploretheopen

environment.Astheopenareacontainednoobtainableresources(suchasfood

patches,refugia,orpotentialmates),therewerenopotentialrewardsfor

exploringtheopenenvironmenttowardstheendofthetrials.Onceanindividual

hadsampledtheenvironmenttothepointwhereitcouldbeconcludedthat

therewerenoavailableresourcespresent,themostoptimaluseofenergywas

likelyforanindividualtoabortexploringthatenvironment(Lima1984),andto

reducetheiroverallactivity.Inenvironmentswithfoodpatches,thiswouldbe

similarinmechanismtoanindividualabandoningafoodpatchonceitreaches

themarginalcapturerate,astheenergyreturnsarenolongerworththeenergy

costofforagingwithinthatpatch(Cowie1977).Thatistosay,thatoverthe

courseofthetrials,individualsmayhavebecomedesensitizedtotheopenarea,

andthiscouldexplainthelackofevidenceofhabituationacrossmanyofthe

groupsinthisstudy.Itisalsorationaltoconcludethatthebestareastobe

inactivewithinthetesttankwerewithintherefuges,asindividualscouldstill

33

receivetheantipredatorbenefitsthattherefugeprovides,whilstalsoconserving

energy.

Aswellastherebeingnosignificantdifferenceinthedegreesofhabituation

acrossallgroupsinthestudy,therewasalsonosignificantdifferenceinhow

collectivelygroupsbehavedbetweenthebeginningandendofthetrials.This

suggeststhat,overall,therewerenosignsofdeteriorationincollectivenessas

thetrialsprogressed.Adeteriorationincollectivenesswouldbeexpectedif

habituationhadoccurredoverthecourseofthetrial,inlinewiththefindingsof

MillerandGerlai(2012),wherebyzebrafishtendedtomorefrequentlyform

disorganizedshoalsoverorganizedschoolsastheyhabituatedtoanovel

environment.Asexhibitingantipredatorbehaviourisnotnecessaryfollowing

habituationtoanenvironmentwithnopredatorspresent,individualsmay

benefitthemost(intermsoffitness)bybehavinglesscollectivelyfollowing

habituation,spendingmoretimeforaginginsmallgroups,orevensolitarily,in

ordertoreducefoodcompetition(Hoareetal.2004),however,thisphenomenon

wasnotobservedinthisstudy.

Themostlikelyexplanationforthelackofdeteriorationofcollectivebehaviour

isthatgroupshadnothabituatedtoasignificantenoughdegreewithinthetrial

timeforthecollectivebehaviourofindividualstobeaffected.Itispossiblethat,if

thetrialswerelonger,groupsmayhaveshownsignsofdeteriorationof

collectivenessasthetrialprogressed.

However,anotherexplanationisthat,followinghabituation,groupssimplyspent

lesstimeinahighlycoordinatedschool,andmoretimeinalooselycoordinated,

butequallyascohesive,shoal.ThiswasobservedinMillerandGerlai(2012),

wherebyratherthangroupsundergoingcompletefissionfollowinghabituation,

groupssimplybecamelesspolarised,andspentmoretimeinalooser

configuration.Ourdataonlyallowedustoidentifywhetheragroupwasspatially

separated(i.e.whethergroupsexistedacrossmorethanoneoftheenvironments

withintheexperimentaltank)atanytimeduringthetrial,anddidnotallowusto

differentiatebetweenlevelsofpolarization(e.g.schoolingandshoaling)reliably.

34

Inafurtherstudy,trackingsoftwarecouldbeusedonourtrialvideos(similarto

thatusedinstudiessuchasMcDonaldetal.(2016),inordertoidentifythe

directionthateachindividualwasfacingatanytimethroughoutthetrial.This

wouldallowustocalculateagroup’sdegreeofpolarization,andmayallowusto

reliablydifferentiatebetweenschoolingandshoalingbehaviour.

Insummary,ourdatasupportsthepresenceofconsensusdecision-makingin

sticklebacks,asallindividualswithinagrouptendedtopreferentiallyuseoneof

twoidenticalrefuges.Thisstudysupportsthehypothesisthesharingofsocial

informationfacilitatesgroupsthatbehavecollectivelytohabituatetotheir

environmenttoagreaterdegreethangroupsthatbehavelesscollectively.

However,therewasnoevidenceofdeteriorationingroups’collectivenessasthe

trialsprogressed,andourresultssuggestthathabituationdidnotoccurinover

halfofthegroupstrialed.Somepotentialmechanismsthatmayhaveprevented

groupsfromshowingsignsofhabituationhavebeenidentifiedanddiscussed.

Furtherstudiescouldinvestigatemoresubtlechangestoagroup’scollectiveness

astheyhabituatetoanenvironment,suchasadifferenceinagroup’s

polarization(thatis,theirtendencytoexistasaschoolorashoal)overthe

courseofatrial.

35

DataChapter2:Investigatingtheinteractionbetweensociabilityandenvironmentalhabituationinindividualsticklebacks(Gasterosteusaculeatus)

IntroductionDataChapter1investigatedtheinteractionbetweentheperceivedriskof

predationinanenvironmentovertime,andhowthisinteractedwiththe

collectivebehaviourofagroupofsticklebacks.Thepurposeofthisfirststudy

wastoexaminewhethergroupsthatbehavedcollectivelycouldutilisesocial

informationfromconspecificstohabituatetoanenvironmentfasterthangroups

thatbehavedlesscollectively.However,becauselocalinteractionsbetween

groupmembersarehighlycomplexandoccuratsuchafastratewithinaschool

orshoal,itisverydifficulttoinvestigatetheprocessesbehindinformation

transferbetweengroupmembers,withouttheuseofindividualtracking(e.g.

Strandburg-Peshkinetal.2013)orcomputer-basedmodelling(e.g.Couzinetal.

2005).

Itisalsolikelythattheremaybefactorsthatproducedifferencesinhabituation

ratesnotonlybetweengroups,butalsobetweenindividuals.Thesefactorsare

alsodifficulttoinvestigateusingagroup-basedstudy,suchasthatusedinthe

firstdatachapter,asstudieshaveshownthatindividualdifferencesinbehaviour

(i.e.personalitydifferences)canbesuppressedinagroupsetting(McDonaldet

al.2016).Thissecondstudywillexaminetheseindividualbehavioural

differences,andinvestigatehowbehaviouraldifferencesbetweenindividuals

affecteachindividual’srateofenvironmentalhabituation.

Inter-individualdifferencesinbehaviour,whichareconsistentovertimeand

acrosscontexts,aresaidtoconstituteaspectsofanindividual’spersonality(Bell

36

2005).Evidenceofindividualpersonalityhasbeenfoundinseveralvertebrate

taxa,includingbirds(Dingemanseetal.2002),mammalsincludingprimates,

mustelids,dogs,rodents,andlivestock,andfish(forareview,seeGosling2001).

Onebehaviouraltraitthathasbeenshowntobeconsistentwithinanindividual

overtimeandacrosscontextsisboldness.Boldnesscanbedefinedasthe

willingnessofanindividualtotakerisksinordertopotentiallyreceivegreater

rewards.Thepositionofanindividualontheboldness/shynessaxisislinkedto

itstendencytoexhibitarangeofbehaviours,andthesetendenciesareconsistent

acrosstimeandcontexts(Bell2005).Forexample,studieshavefoundthat

bolderindividualsareconsistentlymorepredisposedtoexploratorybehaviour

thanshyerindividuals(Budaev1997);resumeforagingfasterthanshyer

individualsfollowingapredatorattack(Websteretal.2007);andaremore

aggressivetowardsconspecificsandboldertowardspredators(Huntingford

1976).Studieshavealsodemonstratedthatbolderindividualshabituatefasterto

anovelenvironment,suchasanexperimentaltank(Wilsonetal.1993).

Together,thesebehaviouraltendenciesassociatedwithanindividual’sboldness

areknownasabehaviouralsyndrome(Bergmüller2010).

Wardetal.(2004)investigatedthepresenceofboldnessasapersonalitytraitin

sticklebacks,byexaminingtheirbehaviouracrossfoursocialcontexts.Thestudy

foundthatindividualsthatresumedforagingfasterafterapredatorattackalso

exhibitedlowmotivationtobehavecollectively.Theseindividuals(whowhere

consideredtobebold)exhibitedafastergrowthratethanindividualsthatwere

deemedtobeshy,andconsistentlyoutcompetedshyerindividualsforfood.This

studydemonstratesthatsticklebacksshowevidenceofpersonality,as

individualsvariedintheirpositiononthebold/shyaxis,andboldandshy

individualsexhibitedconsistentdifferencesinbehaviouracrossseveralcontexts.

Thisstudyalsodemonstratesthatinter-individualdifferencesinbehaviourcan

havefitnessconsequences.Byoutcompetingshyerindividualsforfoodand

exhibitingafastergrowthrate,bolderindividualsobtainedadvantagesover

shyerindividualsthatdirectlybenefittedtheirfitness.Thisposesaquestion:if

37

beingboldconsistentlyprovidedfitnessbenefitsacrosscontexts,onewould

expectnaturalselectiontoconsistentlyfavourbolderindividuals,resultinginthe

boldness/shynessaxisbeingevolutionarilyunstable.However,itseemsthat

boldnessmaybenegativelycorrelatedwithanindividual’ssurvivalrate(Smith

&Blumstein2008),perhapsasaresultofthetendencyofbolderindividualsto

takegreaterrisks.Thereisalsoevidencethatfluctuatingenvironmental

conditions,suchasavailabilityoffoodandvariationinpopulationdensity,

producestemporalandspatialchangesinselectionpressure,whichmayfavour

eitheraboldorshystrategy(Dingemanseetal.2004).Thesestudiesindicatethe

presenceofatrade-offinfitnessconsequencesbetweenboldandshystrategies

thatallowsaboldness/shynessaxistobeevolutionarystable,andhencefor

inter-individualdifferencesinboldnesstobemaintainedwithinpopulations.

Studieshavealsoprovidedevidenceforsociabilitybeingapersonalitytraitin

certainspecies.Forexample,CoteandClobert(2007)investigatedthesociability

ofcommonlizards(Lacertavivipara).Individualsinthisstudyexhibitedinter-

individualvariationintheirsocialtolerance(sociability),whichwasconsistent

overtheirlifetimeandacrosssocialcontexts.

Previousstudieshavedemonstratedthatpersonalitytraitssuchasboldnessand

sociabilityinteractinseveralways.Forexample,theboldnessofanindividual

influencesthespatialpositionthatitmaytakeupwithinagroup(Wardetal.

2004;McDonaldetal.2016).Thepositionofanindividualwithinagroup

conveyscertaincostsandbenefits.Forexample,individualstowardsthemiddle

ofagroupmayreceivethebestantipredatorbenefits,astheyarelessvulnerable

toanattackthanindividualsatthefrontofagroup,buttheysufferintermsof

potentialtoforage,asindividualsatthefrontofagroupwillhavefirstaccessto

discoveredfoodpatches.Bolderindividualstendtotakeuppositionsatthefront

ofagroup(Wardetal.2004),wheretheyreceivepotentiallygreaterrewards

(McDonaldetal.2016),butatthecostofahigherriskofpredation(Bumannet

al.1997).Anotherinteractionbetweenindividuals’boldnessandsociability

traitswasdemonstratedinKurversetal.(2010),wherebybolderbarnaclegeese

(Brantaleucopsis)werefoundtoutiliseavailablesocialinformationtoalesser

38

extentthanshyerindividuals.Previousstudieshavesuggestedthatshyer

individualspaycloserattentiontothebehaviourofnearbyconspecifics,and

thereforemaycollectmoresocialinformationandutiliseittoagreaterextent

thanbolderindividuals(Stowe&Kotrschal2007;Harcourtetal.2009;Kurvers

etal.2010),howeverthisisdisputedbyotherstudies,whichsuggestthat

variationinboldnessdoesnotaffectindividual’suseofsocialinformation

(Harcourtetal.2010).Asstudieshavefoundthatsociabilityandsocialtolerance

isapersonalitytrait(CoteandClobert2007;Rodriguez-Prietoetal.2010b),and

thereissomeevidencethatanindividual’sboldnessisrelatedtotheir

propensitytoutilisesocialinformation(Kurversetal.2010),itisalsolikelythat

anindividual’ssociabilitymayberelatedtotheirpropensitytoutilisesocial

information.

Studieshavealsoshownthatindividualswithinapopulationvaryintheirinnate

abilitytohabituatetostimuli(Runyan&Blumstein2004;Ellenbergetal.2009).

Itislikelythatthishabituationabilityformsanaspectofabehaviouralsyndrome

thatistiedtoanindividual’spersonalitytraits,suchasboldnessandsociability

(Rodriguez-Prietoetal.2010b).Thisseconddatachapterusedanindividual-

baseddesign,withonefocalfishpertrial,inordertoinvestigatetheinteractions

betweenanindividual’ssociabilityanditsrateofhabituationtoanovel

environment.Thisindividual-baseddesignalsoallowedustoinvestigatethe

effectoftheboldnesspersonalitytraitonthesefactors.

Thetrialswithinthisstudyoccurredoverthreeconsecutivedays.Onthesecond

day,asmallgroupofconspecificswasintroducedtoanenclosurewithinthe

openareaofeachtriallane,sothatthefocalindividualcouldseeandapproach

theconspecificswithintheopenarea,butnotdirectlyinteractwiththem.

Althoughthefocalindividualcouldnotinteractwiththeconspecifics,an

individual’ssociabilitycouldbeassessedthroughthetimethatitchosetobein

closeproximitytotheconspecificgroup.

Itislikelythatthepresenceoftheconspecificswithintheopenareawouldalso

producesocialinformationthatthefocalindividualcouldreceiveandinterpret.

39

Forexample,thepresenceofconspecificswithinthe‘risky’openarea

permanentlythroughoutthetrialonDay2mayhaveactedasasocialcue,andbe

interpretedbythefocalindividualasanindicatorofthesafetyoftheopenarea.

Thisisaninterestingaspectof‘informationtransfer’,asthetermisnormally

appliedtoinstanceswhereinformedindividualsgeneratesignalsorcues

(intentionallyorotherwise),whicharethentransferredtouninformed

individuals.Inthiscase,theinformationthatthe‘informed’conspecificswithin

theenclosurepossessed(i.e.thesafetyoftheopenenvironment)wasartificial,

asthegroupwaskeptwithinanenclosureintheopenarea.Thisallowedus,toa

degree,togeneratesocialcuesthatthefocalfishcouldreceiveandinterpret.

Highlysociableindividuals(i.e.individualswhospentthemosttimearoundthe

conspecificshoalonDay2)weremorelikelytobepickinguponandutilisingthe

cuespresentedbythepresenceoftheconspecificshoalwithintheopenarea,as

theywerewithinacloserproximitytotheshoalforagreaterduration.

Ourmainhypothesisforthisstudywasthatindividualswhoexhibitedthe

highesttendencytosocialisewiththeconspecificshoalonDay2ofthe

experimentwouldshowthegreatestdegreeofenvironmentalhabituationover

thecourseofthethreetrials.Thiswouldsuggestthattheinformation

transferredtothefocalindividualwhilstinproximitytotheconspecificshoal

(i.e.thepositionalcueoftheshoalwithintheopenarea)facilitatedafasterrate

ofenvironmentalhabituationthanthatexpressedbyotherfocalindividualswho

exhibitedalessertendencytosocialise,andthereforeutilisedtheavailablesocial

informationtoalesserextent.

Asthisstudywascompletedoverthreeconsecutivedays,thisdesignallowedus

toalsoinvestigatewhetherindividuals’showedconsistentlevelsof

boldness/shynessoverthedurationofthetrials.Aswellasinvestigatingthe

relationshipbetweenanindividual’ssociabilityanditsrateofhabituation,this

studyalsoinvestigateswhetheranindividual’stendencytoexploretheopen

areawasconsistentoverthecourseofthetrials.Ifthiswerethecase,thiswould

providefurtherevidenceforboldnessbeingapersonalitytraitinsticklebacks.

Furthertothis,wealsoinvestigatewhetherbolderindividualstendedto

40

habituatetothenovelenvironmentfasterthanshyerindividuals.Fromthe

findingsofpreviousstudies,wehypothesisethatindividualsthataremeasured

tobebolderwillbesignificantlylesssocialthanshyerindividuals(i.e.spendthe

leasttimearoundtheconspecificsonDay2)inlinewiththefindingsofWardet

al.2004),andwillalsohabituatetotheenvironmenttoasignificantlygreater

degreethanshyerindividualsoverthecourseofthethreetrials(inlinewiththe

findingsofWilsonetal.1993).

Methods

ExperimentalSubjectsThree-spinedsticklebacks(Gasterosteusaculeatus)werecaughtfromtheRiver

CaryinSomersetbetweenSeptember-November2016.Thesubjectswereheld

in90Ltanks(70cmx40cmx35cm)inatemperature-controlledroom(water

temperaturewas15-17degreescentigrade),withcontrolleddailyphotoperiods

of12hours.Thepopulationusedinthisstudywerefedbloodworm(Glycerasp.)

oncedaily,followingthecompletionofalloftheday’strials.Thisexperiment

used40individualsfromalargercaptivepopulation.

ExperimentalTankFivetankswereusedtohousetheexperimentalsubjectseachweek.Abreeding

net(asmallenclosednetthatallowsyoutoisolatespecificindividualswithina

largertank)wassetupatthefrontofeachtank,whichwasusedtohousethe

focalfishforeachweek.Thetanksalsocontainedotherconspecifics(between4

and6),whichwereoutsideofthebreedingnets.Theseconspecificswerenot

trialedduringthisstudy.

Theexperimentaltankwas137cmlongand72cmwide,andwassplitintotwo

identicallanesmeasuring36cminwidth,whichwereseparatedbyanangled

partition.Twoidenticallaneswereusedforefficiencywhenrunningtrials(as

thisallowedustoruntwotrialssimultaneously),andthisdesignwasnot

relevanttotheaimsofthestudy.Thepartitionbetweenthetwolaneswas

opaqueinordertoensurethatindividualscouldnotseeorobtaininformation

fromindividualsintheadjacentlane.Thispartitionwasmadefromtwopiecesof

41

Perspexplastic,whichwerefixedtogetheratanangle,sothatthebaseswere

2cmawayfromthemidlineofthepartition.Thiswasdonetominimizetheblind-

spotsofthesingleoverheadcamerawhenfilmingtrials.Thetankwasina

temperature-controlledroom,andthewaterwasmaintainedatatemperatureof

15-16degreesCelsius.

Onerefugewassetupinacentralpositiononthefarwallofeachlane,11cm

fromeachsidewall.Therefugewasmadefromblackcorrugatedplasticandwas

fixedinpositionbysmallmagnetsonthewallandtherefuge.Therefugeswere

10cmwide,8cmhigh,and10cmdeep.Astherefugeswereremovedonday2of

thetrials,magnetswereusedtoensurethattherefugescouldbefixedinan

identicalpositionwhentheywerereplaced.

Ontheotherendofeachlane,atransparentcylindricalenclosure(11.5cmhigh,

withadiameterof10cm)madefromacrosssectionofa2Lplasticbottlewas

fixedinplacewithtape.Theenclosurewasfixed12cmfromthebackwallineach

lane,inacentralposition.Theseenclosureswerehigherthanthewaterlevelin

ordertopreventfishfromescaping,andwerepiercedwithsmallholesto

facilitatewaterflow(andhenceodourcues)withwaterintheenclosure.Figure

6showsthedesignoftheexperimentaltankwiththerefugesinplace.

Thetankwasonasurfacewithaslightslope,buttherewasaconstantwater

levelof10cmattherefugeendofthetankand7cmatthecylinderend

throughoutthetrials.Theentiretankwasilluminatedbytwotubelights

(Masterlitefluorescent13Wlinkablecabinetlight,585mminlength),which

werefixedinplace12cmaboveeachendofthetank.Trialswererecordedusing

aGoProHeroSessioncamerathatwasfixedinplace80cmabovethetankona

cameramount.

42

Figure6:Stillimagestakenfromtrialvideos.Thefirstimage(left)depictstheexperimentalset-uponDay1andDay3ofthetrialswiththerefugesinplace,andthesecond(right)depictstheset-uponDay2,withtherefugesremovedandconspecificsplacedintheenclosures.

ExperimentalProtocolOnaMonday,individualswererandomlyselectedfromalargerpopulationof

sticklebacks,andpairsoffishwereplacedintoeachofthefivebreedingnets.

Fishwithnoticeabledifferencesinsizewerepairedtogetherwithinabreeding

net,andeachindividualinapairwasassignedeitheras‘L’or‘S’(LargeorSmall),

dependingonitssizerelativetotheotherindividualinitspair,asthismadeit

possibletoidentifyeachindividualwithinthesamebreedingnet.Thiswas

important,asindividualshadtoberecognizableinordertobetrialedoverthree

consecutivedays.Eachpairwasassignedabreedingnetthatwaskeptconstant

overthecourseofthethreedaysthattheyweretrialed.Fishwithinthefive

holdingtankswerefedasnormalonaMonday,butfoodwasonlyprovidedafter

trialshadtakenplaceonthetrialdays(Tuesday,WednesdayandThursday).

Day1andDay3Onthefirstdayoftrials(Tuesday),apairoffishwastakenfromabreedingnet,

andeachindividualwasplacedintooneofthetwolanesintheexperimental

tank.Thelanethateachfishfromapairwasplacedintowasrandomlyallocated

bytheflipofacoin(witha‘heads’resultinginthelargerofthetwofishbeing

placedinthefirstlane).Thefishwereplacedintotheopenareaoftheirlane

usingasmallnet.Therewerenofishpresentwithinthecylindricalenclosureon

Day1andDay3oftrials(SeeFigure7).Screensmadefromcorrugatedplastic

werethenplacedoverthetrialareainordertominimisedisturbancetothefish

forthedurationofthetrial.

Eachtrialwasrecordedfor21minutes;however,thefirstminuteofeachtrial

43

videowasdiscountedfromanalysis,asthefishwereintroducedtothetank

withinthisperiod.Thisalsoallowedsometimeforthefrightresponsesthatcan

beinducedwhenhandlingtheindividualstosubside.Followingcompletionof

thetrial,thepairoffocalfishwastranslocatedbacktotheirassignedbreeding

netwithintheholdingtanks.

Day2OnDay2ofeachweekoftrials,therefugeswereremovedfromeachlane.Three

randomlyselectedfishfromalargerpopulationwereplacedintoeachofthe

cylindricalenclosuresonDay2ofeachweek.Thesewereplacedintothe

enclosuresatthestartofeachday,andwerelefttoacclimatisetothetesttank

foraround30minutesbeforeanyoftheday’strialsbegan.Onetestfishwasthen

introducedtoeachlane,followingthesameprocedureasthatusedonDay1and

Day3.EachtrialonDay2alsolasted21minutes,toallowthefocalfishtobe

introducedtothetankandfortheinitialfrightresponsetosubside.Ten

individuals(fromfivepairs)weretrialedeachweek,withatotalof40

individualsbeingtrialedoverthecourseofthestudy.

Figure7:Illustrationdetailingthesetupoftheexperimentaltankthroughoutthetrials.Format(a.)representsthesetupthatwasusedonbothDay1andDay3oftrials,and(b.)representsthesetupusedonDay2.

DataAnalysisThestatisticaltestsconductedwithinthisdatachapteruseasymptoticp-values

unlessotherwisestated.

44

Day1andDay3Thetrialvideoswereanalysedfollowingthecompletionofalltrials.Thevideos

wereviewedat2xspeedoniMoviesoftwareonalaptop.ForvideosfromDay1

andDay3ofthetrialseachweek,thedurationthateachindividualspentoutside

oftherefugewithintheirlanewasrecorded.Thiswasrecordedbyeye,using

twostopwatchessimultaneously;oneforeachfishineitherlaneofthetesttank.

Toproduceaquantitativemeasureofanindividual’sdegreeofhabituationover

thecourseofthethreetrials,thetimethatanindividualspentoutsideofthe

refugeonDay3wassubtractedfromtheirtimespentoutsideoftherefugeon

Day1.

Day2Duringdataanalysis,thedurationthateachfishwaswithinonebodylengthof

thecylindricalenclosure(containingthethreeconspecifics)onDay2was

recorded.Theproximitytothecylindricalenclosurewasestimatedbyeye.This

wasusedasameasureofhowsociableeachindividualwasonDay2ofthetrials,

wherebyfishthatspentmoretimeclosetotheirconspecificswithinthe

enclosureweredeemedmoresociablethanthosethatspentmoretimeinother

areasofthetank,awayfromtheirconspecifics.

MeasureofIndividualBoldness

Theaveragetimespentoutsideoftherefugeswascalculatedforeachindividual,

fromthetimethattheyspentoutsideoftherefugesonDay1andDay3oftrials.

Thiswasusedasabasicquantitativemeasureofanindividuals’relative

boldnessoverthecourseofthetrials,wherebyindividualsthatonaveragespent

moretimeexploringthe‘risky’openareaonDay1andDay3weredeemedtobe

bolderthanthosethatspentmoretimewithintherefugesonthesedays.

45

Results

TestingthekeyassumptionofhigherperceivedriskinopenareasTheassumptionthatsticklebacksfindopenareasinherentlymore‘risky’than

refugiawasakeyassumptionofthisstudy,aswellasinthefirstdatachapter.

Thisassumptionwastestedbyinvestigatingthemeanproportionofthetotal

trialthatindividualsspentinbothenvironmentswithinthetesttank.Themean

percentageofthetrialsthatindividualsspentwithintherefugewas53.4%and

62%forDay1andDay3respectively.Giventhattheareawithintherefugeonly

constitutedasmallproportionofthetotalareaofthetestlanethateach

individualhadaccessto(therestofwhichcomprisedtheopenarea),this

suggeststhatindividualsdidspendadisproportionateamountoftimewithinthe

refugeincomparisontothatwhichwouldbeexpectedifbothenvironments

wereseenashomologous,indicatingthatthefocalfishlikelydidperceivethe

openareasasinherentlymore‘risky’thantherefuge.

Wasanindividual’ssociabilityagoodpredictoroftheirdegreeofhabituation?Therewasfoundtobenosignificantcorrelationbetweenindividuals’degreeof

habituationtotheopenarea(thedifferenceintimespentoutsideoftherefuges

betweenDay1andDay3),andthetimeeachindividualspentincloseproximity

totheconspecificgroupwithintheenclosuresonDay2(Spearman’srank,n=20,

R=-0.006,p=0.973).Thissuggeststhatthesociabilityofindividualswasnota

suitableindicatorofthedegreeofhabituationthattheyexhibitedoverthe

courseofthetrials.

46

Figure8:ThechangeintimespentoutsideoftherefugebetweenDay1andDay3,relativetothesociabilityofeachindividualonDay2.NotethatpositiveyvaluesdenoteanincreaseintimespentoutsideoftherefugesbetweenDay1andDay3(indicatingadegreeofhabituation),andnegativevaluesdenoteareductionintimespentoutsideoftherefugesbetweenDay1andDay3.

Figure8showsthatindividualsthatexhibitedsimilarlevelsofsociability(thatis,

individualswhospentasimilardurationofthetrialonDay2incloseproximity

totheenclosurewiththeconspecificsinside)displayedalargedegreeof

variationinthedegreeofhabituationthattheyexhibitedbetweenDay1andDay

3.Figure9displaysthevariabilityintheresponsevariablesbetweenindividuals

acrossDay1,2,and3ofthetrials.Itisclearthattherewasalargedegreeof

variationintheproportionoftotaltrialtimethatindividualsspentoutsideofthe

refugeonbothDay1andDay3(std(Day1)=0.337;std(Day3)=0.318).

However,itisalsoclearthatthedegreeofvariationintimethatindividuals

spentwiththeirconspecificsonDay2wasmuchsmaller(std(Day2)=0.101).A

Brown-Forsythetestwasconductedtoestablishwhetherthevariabilitybetween

thesociabilityofindividualsandthedifferenceintimethattheyspentoutsideof

100 200 300 400 500 600 700

-500

0500

1000

Time Spent Socialising on Day 2

Diff

eren

ce in

Tim

e S

pent

Out

side

of t

he R

efug

e B

etw

een

Day

1 a

nd D

ay 3

47

therefugesonDay1andDay3,wereequal(Brown&Forsythe1974).The

varianceinthesociabilityofindividualswasfoundtobesignificantlylowerthan

thevariancethatexistedbetweentheboldnessofeachindividualduringDay1

andDay3(F=6.478,DF=2,p=0.002).Thissuggeststhattheindividualssampled

withinthisstudywererelativelyanalogousintermsoftheirsociability,but

variedmuchmoresignificantlyintheirindividualboldness.Itseemsthatthis

combinationofhighvariabilityinindividualboldnessandlowvariabilityin

individualsociabilitymayhavecontributedtothelackofasignificantcorrelation

betweenindividual’ssociabilityandthedegreetowhichtheyhabituatedtothe

environmentoverthecourseofthetrials.

Figure9:BoxplotshowingthevariationintheproportionofthetotaltrialtimethatindividualsspentoutsideoftherefugesonDay1andDay3,andsocializingwiththeirconspecificsonDay2.

ThehighdegreeofvariabilityinthetimespentoutsideoftherefugesonDay1

andonDay3alsosuggeststhatsomeindividualsmaynothavehabituatedtothe

novelenvironmenttoasignificantdegreeoverthecourseofthetrials(assome

individualsspentverylittletimewithinthe‘risky’openareaonbothDay1and

Day3).Apairedt-testwascarriedoutonthetimethateachindividualspent

outsideoftherefugebetweenDay1andDay3oftrials.Thepurposeofthis

analysiswastodiscernwhetherindividualssignificantlyincreasedthetimethat

theyspentoutsideoftherefugesoverthetestingperiod,whichwouldsuggest

thathabituationtothetestenvironmenthadtakenplace.Acrossallindividuals,

therewasnosignificantdifferencebetweenthetimespentoutsideoftherefuges

48

onDay1andDay3(Pairedt-test,t=1.670,DF=39,p=0.103).

Thissuggeststhatsomeofthesampledindividualshadnothabituatedtothetest

environment.ThisissupportedbyFigure8,whichshowsthatfifteenindividuals

spentmoretimeoutsideoftherefugeonDay3thanDay1(suggestingthatthey

mayhavehabituatedtotheenvironmenttosomedegree),buttwenty-five

individualsspenteitherthesameamountoftime(n=1),orlesstime(n=24)

outsideoftherefugesonDay3thanonDay1,demonstratingthatoverhalfof

theindividualstrialeddidnotexhibitsignsofhabituationbetweenDay1and

Day3.

Figure9alsodemonstratesthatthemedianproportionofthetrialspentoutside

oftherefugeacrossallindividualsisloweronDay3thanonDay1.Theopposite

trendwouldbeexpectedifhabituationhadoccurred,asonewouldexpect

individualsto,onaverage,spendahigherproportionofthetrialoutsideofthe

refugeonDay3thanDay1.

EvidenceofboldnessbeingapersonalitytraitinsticklebacksThetimethateachfishspentoutoftherefugeonDay1andDay3wasstrongly

positivelycorrelated(Spearman’srank,n=20,R=0.542,p<0.001).Thissignificant

correlationindicatesthatindividualstendedtoberelativelyconsistentintheir

choiceofwhethertospendtheirtimewithinoroutsideoftherefugesacrossDay

1andDay3.Figure10belowshowstwointerestingpointsthatbothsupportthe

presenceofaboldness-shynesscontinuumwithinthesampledpopulation.

Firstly,therewasconsiderablevariationbetweenindividualsintheproportion

ofthetrialsthattheyspentoutsideoftherefugesonDays1and3,suggesting

thatinherentlyboldandshyindividualsexistedwithinthesamplepopulation

(thisvariabilityisalsoseeninFigure9);andsecondly,thatindividualswere

relativelyconsistentintheproportionofthetrialsthattheyspentoutsideofthe

refugeacrossDay1andDay3,indicatingthatindividualswereconsistentlybold

orshyoverthetrialperiod.

49

Figure10:ScatterplotshowingthecorrelationbetweentheproportionoftimeindividualsspentoutsideoftherefugesonDay1andDay3.

Astheboldnessofindividualswasfoundtobeconsistentovertime,wealso

testedforcorrelationsbetweentheboldnessofindividualsandtheirsociability

(i.e.thetimespentincloseproximitytotheconspecificshoalonDay2);aswell

asbetweenanindividual’sboldnessandthedegreeofhabituationthatthey

exhibited.However,anindividual’saverageboldnessacrossDay1andDay3was

notsignificantlycorrelatedwiththeirsociabilityonDay2(R=0.105,p=0.518),or

withthedegreeofhabituationthattheyexhibited(R=-0.151,p=0.354).

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

Proportion of Day 1 Trial Spent Outside of the Refuge

Pro

porti

on o

f Day

3 T

rial S

pent

Out

side

of t

he R

efug

e

50

Discussion

TestingtheKeyAssumptionofOpenAreasBeingAssociatedWithaHigherPerceivedRiskofPredationFocalindividualsspentonaverageoverhalfoftheirtimewithintherefuge,

ratherthantheopenareasofthetank,onbothDay1andDay3ofthetrials.The

assumptionthatopenareasareperceivedascarryingahigherriskofpredation

thanrefugiaunderpinsmanypreviousstudiesonsticklebacksinbehavioural

ecology.Forexample,McDonaldetal.(2016)usedtheassumptionthattheactof

sticklebackscrossinganopenarenatoreachafoodsourcewouldbeamorerisk-

pronebehaviourthaninitiallyleavingarefuge,asindividualsaremoreexposed

andvulnerabletopredationwithinanopenareathanwhenclosetoarefuge.

Similarly,Harcourtetal.(2009)andIoannouetal.(2008)bothquantifiedthe

boldnessofindividualsticklebacksbytheirtendencytoleavearefugeandenter

anopenarea.Giventhattheuseofrefugiaandopenareasissuchanestablished

conceptinbehaviouralecology,andthattheindividualstrialedinthisstudy

occupiedtherefuges(averysmallproportionofthepotentialareathatcouldbe

occupied)foronaverageoverhalfofthetotaltrialtimeonbothDay1andDay3,

itisconsideredlikelythattheindividualsinthisstudydidfindtheopenspace

moreinherentlyriskythantherefuges,andthereforetheuseofthisassumption

inthisstudywasreasonable.

TheInteractionBetweenIndividualSociabilityandHabituationOurkeyhypothesisstatedthathighlysociableindividualswouldreducetheir

perceivedriskoftheopenenvironmentatarelativelyfasterratethanless

sociableindividuals.Themainmechanismthatwasconsideredwasthathighly

sociableindividualswouldreceiveandutilisethesocialcuesobtainedfromthe

locationoftheconspecificshoalwithintheopenenvironmentonDay2toa

greaterdegreethanlesssociableindividuals,andthuswouldreducetheir

perceivedriskoftheopenenvironmenttoagreaterdegreethanlesssociable

individuals,whowouldnothavehadaccesstothissocialinformationtothe

sameextent.However,thisstudyfoundnosignificantcorrelationbetween

individuals’sociabilityandthedegreetowhichtheyhabituatedoverthecourse

ofthetrials.ThelackofvariabilityinindividualsociabilityonDay2maybea

contributingfactortothelackofasignificantcorrelationbetweenindividuals’

51

sociabilityandtheirrateofhabituation,ascorrelationtestsrequireareasonable

degreeofvariabilityinbothvariablestoproducesignificantresults.

Ourresultsalsosuggestthatmanyoftheindividualstrialeddidnothabituateto

thenovelenvironmentoverthecourseofthetrials.Thiswasindicatedbythe

lackofasignificantdifferencebetweenthetimethatanindividualspentoutside

oftherefugebetweenDay1andDay3,aswellasthefactthattwenty-fiveofthe

fortyindividualsinthisstudyeitherspentthesameamountoftime(one

individual),orlesstime(twenty-fourindividuals),outsideoftherefugesonDay

3thanonDay1.Thismakesitdifficulttodrawconclusionsaboutthe

relationshipbetweenindividual’ssociabilityandtheirrateofenvironmental

habituation,asthenumberofindividualswhodidshowsignsofhabituationin

thisstudywastoofewtoproducestatisticallysignificantcorrelationsand

analysesbetweenourvariables.However,itisworthnotingthatthedifference

betweenthetimethatindividualsspentoutsideoftherefugeonDay1andDay3

hadarelativelylowp-value(pairedt-test,p=0.103),whichmayindicatethata

trendispresent,butwasnotstatisticallysignificantinthisstudy.Giventhatour

dataisrelativelynoisy,itispossiblethatastudywithalargersamplesize,for

example,wouldrevealasignificantdifferencebetweenthesetwovariables.

Onepotentialreasonforthelackofhabituationtothenoveltrialenvironmentis

thatthedurationofeachtrialwastooshort,attwentyminutespertrial.

Althougheachindividualwasexposedtothreetwentyminutetrials(resultingin

eachindividualhavingsixtyminutestotalwithinthenovelenvironment)over

threeconsecutivedays,itispossiblethat,wereeachofthetrialslonger,ahigher

degreeofhabituationwouldhavebeenobservedoverthedurationofthestudy.

Forexample,MillerandGerlai(2012)observedahabituationeffectinzebrafish

(Daniorerio)overtheperiodofacontinuoustrialthatlastedfourhours,aswell

asoveraseriesoffivedailytrials,whichlastedforthirtyminuteseach.Inbothof

thesemethodologies,thefocalfishwereexposedtothenovelenvironmentfora

longerdurationthanthefocalfishusedinthisstudy,andthushadmoretimeto

habituatetotheenvironment.AlthoughMillerandGerlai(2012)usedadifferent

speciesoffishwithadifferentexperimentalprocedure,itisstilllikelythat

52

individualsinthisstudymayhaveexhibitedagreaterdegreeofhabituationover

alongertrialperiod,andfurtherstudiesshouldtakethisintoaccount.The

groupsofindividualstrialedinthefirstdatachapterdidshowsomesignsof

habituationoverasingletrialperiodofthirtyminutes;however,these

individualsweretestedingroups(ratherthansolitarily,asinthisdatachapter),

andassuch,itisdifficulttodeduce,withanycertainty,whetheratriallengthof

thirtyminuteswouldhaveproducedahigherdegreeofhabituationinthisstudy.

Anotherpotentialexplanationforthelackofanincreaseinexploratory

behaviouroverthecourseofthetrials(and,indeed,theobservedreductionin

exploratorybehaviouracrossthecourseofthetrialsintwenty-fouroftheforty

individualstrialed)isthattheindividualshadexploredthenoveltank

sufficientlyonDay1andDay2todeducethattheopenareacontainedno

availableresources.Asnofoodstimuliwerepresentedwithinthetankatany

timeduringthetrials,adesensitizationeffectsimilartothatpotentiallypresent

inourfirstdatachaptermayhaveoccurred,wherebyindividualsexploredthe

openareauntiltheyhadconcludedthattheenvironmentwasbareofresources,

atwhichpointtheyreducedtheiractivitywithintheopenareainordertoavoid

inefficientuseofenergy(Lima1984).

Infuturestudies,alarger,stochasticenvironmentwithexploitableresources,

suchasfoodpatches,couldbeusedinordertoprovidearewardforexploratory

behaviourofthe‘risky’openareaoverthecourseofthetrial.Asimilar

methodologywasusedinMcDonaldetal.2016,wherebybloodwormswere

releasedintotheopenareaoftheexperimentaltankoncethefocalindividuals

hadleftarefugeandcrossedtheopenarea,thusprovidingafoodrewardto

incentivizeexploratorybehaviour.Theinclusionofafoodincentiveforforaging

individualswouldreducethepossibilityofadesensitizationeffectoccurring,

suchasthatexploredabove,anditispossiblethatindividualswouldincrease

theirexplorationoftheopenareaastheybecamehabituatedtothetest

environment,aswasexpectedinthisstudy.Nevertheless,thisstudyprovides

littleevidencetosupportthehypothesisthatsociableindividualscanutilise

socialinformationtohabituatetoanenvironmentfasterthanlesssociable

53

individuals.

EvidenceforboldnessasapersonalitytraitinsticklebacksThedatacollectedwithinthisstudydoesprovidesomesupportforboldness

beingapersonalitytraitinthree-spinedsticklebacks.Thestrongpositive

correlationbetweenthetimethateachindividualspentoutsideoftherefugeon

Day1andDay3demonstratesthatindividualsexhibitedpersonalities,defined

asinter-individualvariationsinbehaviourthatareconsistentovertimeand

acrosscontexts,overthecourseofthethreedays.Someindividualstrialedwere

consistentlybolderthanothers,exhibitingagreatertendencytospendtimein

theriskyopenenvironmentacrossbothDay1andDay3.Thisresultsuggests

thatanindividual’spositiononthebold-shycontinuumwasrelativelyconsistent

overtime,undersimilarexperimentalconditions.Thisisinlinewiththefindings

ofotherstudies(Wardetal.2004;Ioannouetal.2008),andindicatesthat

boldnessisapersonalitytraitinsticklebacks.

Otherstudieshavefoundthattheboldnessofanindividualislinkedtoits

tendencytoexhibitarangeofotherbehaviours,andthesetendenciesmakeupa

behaviouralsyndromethatislinkedtoboldness.Forexample,inCroftetal.

2009,individuals’boldness(definedasanindividualspropensitytoinspecta

predator)andsociability(thetimeanindividualspentshoaling)werenegatively

correlated,indicatingthatbolderindividualshadconsistentlylowersociability

thanshyerindividuals(Wardetal.2004).Studieshavealsoshownthatbolder

individualsutilisesocialinformationtoalesserdegreethanshyerindividuals

(Kurversetal.2010),andhabituatefastertonovelenvironments(Wilsonetal.

1993).However,inthisstudy,anindividual’sboldnesswasnotcorrelatedwith

theirsociabilityonDay2oftheexperiment,orwiththeirdegreeofhabituation.

Thisstudythereforeprovidesnoevidenceoftheseaspectsofthebehavioural

syndromethatisassociatedwithanindividual’sboldness.

Associabilitywasonlytestedononeday,thisdataisinsufficienttodeduce

whetherthesociabilityofanindividualwasconsistentoveraperiodoftimeor

acrosscontexts,andthuswecan’tdeducewhethersociabilitywasapersonality

traitfromourdata.However,therehasbeenpreviousworkthatsuggeststhatan

54

individual’ssociabilityisconsistentovertime,andisthereforeapersonalitytrait

insometaxa,ashasbeenpreviouslydiscussed(Dalletal.2004;CoteandClobert

2007;Coteetal.2010;Rodriguez-Prietoetal.2010b).Futurestudiescouldtest

individual’ssociabilityoveranumberofdays,inordertoestablishwhether

sociabilityisapersonalitytraitinthree-spinedsticklebacks.

55

ConclusionThedatachaptersinthisthesisusedtwodifferentapproachestoinvestigatethe

samequestion:doesbehavingcollectivelyaffectindividuals’ratesof

environmentalhabituation?Thefirstdatachapterusedagroup-baseddesign,

whereindividualswithinashoalwereabletofreelyinteractwithoneanother.

Thisallowedustostudyaspectsofcollectivebehaviour,suchashowcohesive

groupsarethroughouttheprocessofhabituatingtothenovelenvironmentthat

theyareplacedin.Wehypothesizedthatgroupsthatbehavedmorecollectively

andthatremainedmorecohesivethroughoutthetrialwouldexhibitagreater

degreeofhabituationtothenovelenvironment,andthatthiswouldmanifestas

agreaterincreaseinthedurationthatgroupsspentoutsideoftherefuge,

relativetolesscollectiveandcohesivegroups.

Thisstudyfoundapositivecorrelationbetweengroups’collectivenessandthe

degreetowhichtheyhabituatedtotheopenenvironment.Therateatwhich

individualsorgroupshabituatetoenvironmentscanimpacttheirfitness

(Rodriguez-Prietoetal.2010a),asinvestingtimeandenergyexhibiting

antipredatorbehaviours(suchasshelteringwithinrefugesandforming

polarizedschools)inenvironmentswithnorealthreatofpredationresultsinthe

lossofpotentialforagingtime.Thereareseveralmeansbywhichbehaving

collectivelycanbenefitanindividual’sfitness,withmostoftheseeffectsrelating

toreducingindividuals’predationrisk(forexample,throughdetection,dilution

andconfusioneffects(Elgar&Catterall1981;Lima&Dill1990;Ruxtonetal.

2007;Ioannouetal.2008)).However,thisstudyprovidesevidenceforanother

meansbywhichbehavingcollectivelycanbenefitfitness.Byreducing

individuals’ratesofenvironmentalhabituation,behavingcollectivelycan

increaseindividuals’energyandtimeefficiency,andresultinapotentialbenefit

totheirfitness.Themainmechanismthatwasconsideredtodrivethistrendwas

thatofinformationtransfer,wherebygroupsthatbehavecollectivelycould

transferandutilisesocialinformationtoagreaterdegreethanlesscollective

groups,facilitatingafasterassessmentoftheactualriskofanenvironment.

However,duetothecomplexinteractionsthatoccurbetweenindividualsina

56

freelymovinggroup,thisdesigndidnotallowustotestwhetherinformation

transferwasthekeymechanismthatdrovethecorrelationbetweengroups’

collectivenessandtheirrateofhabituation.Agroup-basedstudyalsodidnot

allowustoinvestigatetheeffectsofindividualpersonalitytraitsontherateat

whichindividualshabituatetonovelenvironments.

Theseconddatachapterusedanindividual-baseddesign,wheretherateof

habituationofafocalindividualwastestedforcorrelationswiththeirtendency

tobehavesocially,aswellaswithanaspectoftheirpersonality(anindividual’s

boldness).Thisstudyallowedustoprovideartificialsocialcuesforthefocal

individualbyplacingagroupofconspecificswithinanenclosureintheopen

area,andinvestigatehowthedegreetowhichanindividualacquiredthis

informationaffectedtherateatwhichithabituatedtothenovelenvironment.

Thisstudyfoundnosignificantcorrelationbetweenanindividual’ssociability

andthedegreetowhichtheyhabituatedtotheenvironment.

Althoughapositivecorrelationbetweengroups’collectivenessatthestartofa

trialandtheirrateofhabituationwasobservedduringthefirstdatachapter,the

majorityofindividualstrialedduringbothofthestudiesdidnotshowsignsof

environmentalhabituationoverthecourseofthetrials.Thismaybeduetosome

limitationsinthemethodsusedinthesetwostudies.Forexample,inboth

studies,nofoodpatcheswerepresentwithintheopenareas.Thisessentially

meantthattherewasnopotentialbenefitassociatedwithexplorationofthe

openarea,whichmayhavedeterredindividualsfromexploringtheopenarea

moreoncetheyhadhabituatedtotheenvironment.Rather,inthesestudies,itis

likelythatthemostoptimaluseofanindividual’senergywastospendmoretime

intherefugesoncetheyhadestablishedthattheenvironmentwasbareof

resources,ratherthanspendmoreenergyexploringthebareenvironment(Lima

1984).Asourmeasuresofhabituationwereallbasedonthetimethatan

individualspentintheopenareaoverthecourseofatrial(wherebygroupswere

consideredtohavehabituatediftheyincreasedthetimespentwithintheopen

areaasthetrialsprogressed),thesemayhavenotbeensuitableindicatorsofan

individual’sdegreeofhabituationintheseenvironments.

57

Thesemethodscanberefinedinfuturestudiesbyprovidingrewardsfor

exploringtheriskyopenarea,suchasfoodpatchesdistributedaroundtheopen

area,orfoodthatisreleasedonceindividualscrosstheopenarea,similartothe

methodusedinMcDonaldetal.(2016).Thiswouldmorecloselyreplicatethe

naturalenvironmentofsticklebacks,wheretherearebenefitstoexploration,in

termsofahigherprobabilitytocomeacrossafoodpatch,aswellascosts,in

termsofahigherriskofpredationinopenareas.

58

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