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Patterns,processes,rates,andconstraints,intheevolutionof morphologicaldisparity Supervisors:PhilipDonoghue(Bristol),MatthewWills(Bath),DavidePisani(Bristol), MariodosReis(QueenMary,London),ThomasGuillerme(Imperial) FromAristotleonwards,ithasbeenapparentthattherearediscontinuitiesin organismalform,suchthatspeciesareclumpedwithinmorphological‘designspace’ [1].Theseclumpsatoncehelpusinattemptstoclassifybutoftenfrustrateour effortstoresolvephylogeny. Thereisvigorousdebateastowhyorganismsareirregularlydistributedinthisway. Doclustersreflectpeaksinaruggedfitnesslandscape?Aretheinterveningregions ofdesignspaceimpossibletocolonise–eitherbecauseofphysicalordevelopmental constraints–oraretheyunoccupiedbecauseinsufficienttimehaselapsed?Were theyonceoccupiedandsubsequentlyvacatedinthewakeofpastextinctions?Isthe rangeofdesigns(morphologicaldisparity)realisedprogressivelythroughtime,orin anearlyburstofinnovationfollowedbystasis?Theanswerstothesequestionshave importantimplications,particularlywhetherthesameprocessesshape macroevolutionthroughoutdeeptime(uniformitarianism)orwhethertheseforces change[2]. Figure:Competingmodelsfortheevolutionofmorphologicaldisparity-from[4] Todate,analyseshavebeenbasedlargelyonempiricalcasestudiesofextinct organisms.Littleattempthasbeenmadetoestablishatheoreticalorempirical foundationforinterpretingempiricaldisparityanalyses.Thisisunsurprising,since methodsforsimulatingtheevolutionofmorphologicaldatahaveonlyrecently becomeavailable[3].Thisprojectwillaugmentthesetoolsinordertosimulate phenotypicevolutionunderthediversityofevolutionarymodelsthatareinferredto haveshapedthemorphologicaldisparityofrealclades.Theseincludeintrinsic factors(suchaschangesinratesofcharacterevolutionandthescaleofinnovation, phylogeneticburden,andlineageduration)aswellasextrinsicfactors(suchas competitionandmassextinctionevents).Theseputativedriversandlimitswillbe examinedinturnandincombinationtodeterminewhethertheyyieldthepatterns ofdesignspaceoccupationthatareobservedinrealclades.Thecandidatewillalso explorehowthestructuralandphylogeneticrelationshipsamongcharacters contributestomorphospaceoccupation. Whiletheintentionistosamplebroadlyacrossorganismaldiversityandthroughout thePhanerozoic.thereisalsoscopetofocusonparticulargroups,dependingupon thesuccessfulcandidate’sinterest. Ultimately,theresultsofthesimulationstudieswillidentifytherelativerolesof differentevolutionaryprocessesinshapingtheoccupationofdesignspace,and provideanewtheoreticalframeworkwithinwhichtoevaluatetheresultsof empiricaldisparityanalyses.Theywillalsospeaktoaseminalcontroversyin macroevolution,namelytheuniformitarian/non-uniformitariandebate. References 1. D.H.Erwin,Disparity:morphologicpatternanddevelopmentalcontext. Palaeontology50,57-73(2007). 2. D.H.Erwin,Evolutionaryuniformitarianism.Developmentalbiology357,2734(2011). 3. J.E.O'Reillyetal.,Bayesianmethodsoutperformparsimonybutatthe expenseofprecisionintheestimationofphylogenyfromdiscretemorphological data.BiologyLetters12,20160081(2016). 4. J.W.Oyston,M.Hughes,S.Gerber,M.A.Wills,Whyshouldweinvestigate themorphologicaldisparityofplantclades?Annalsofbotany,(2015).