Donoghue Evolution of disparity - University of Bristol · range of designs (morphological...

Patterns,processes,rates,andconstraints,intheevolutionofmorphologicaldisparitySupervisors:PhilipDonoghue(Bristol),MatthewWills(Bath),DavidePisani(Bristol),MariodosReis(QueenMary,London),ThomasGuillerme(Imperial)FromAristotleonwards,ithasbeenapparentthattherearediscontinuitiesinorganismalform,suchthatspeciesareclumpedwithinmorphological‘designspace’[1].Theseclumpsatoncehelpusinattemptstoclassifybutoftenfrustrateoureffortstoresolvephylogeny.Thereisvigorousdebateastowhyorganismsareirregularlydistributedinthisway.Doclustersreflectpeaksinaruggedfitnesslandscape?Aretheinterveningregionsofdesignspaceimpossibletocolonise–eitherbecauseofphysicalordevelopmentalconstraints–oraretheyunoccupiedbecauseinsufficienttimehaselapsed?Weretheyonceoccupiedandsubsequentlyvacatedinthewakeofpastextinctions?Istherangeofdesigns(morphologicaldisparity)realisedprogressivelythroughtime,orinanearlyburstofinnovationfollowedbystasis?Theanswerstothesequestionshaveimportantimplications,particularlywhetherthesameprocessesshapemacroevolutionthroughoutdeeptime(uniformitarianism)orwhethertheseforceschange[2].

Todate,analyseshavebeenbasedlargelyonempiricalcasestudiesofextinctorganisms.Littleattempthasbeenmadetoestablishatheoreticalorempiricalfoundationforinterpretingempiricaldisparityanalyses.Thisisunsurprising,sincemethodsforsimulatingtheevolutionofmorphologicaldatahaveonlyrecentlybecomeavailable[3].Thisprojectwillaugmentthesetoolsinordertosimulatephenotypicevolutionunderthediversityofevolutionarymodelsthatareinferredtohaveshapedthemorphologicaldisparityofrealclades.Theseincludeintrinsicfactors(suchaschangesinratesofcharacterevolutionandthescaleofinnovation,phylogeneticburden,andlineageduration)aswellasextrinsicfactors(suchas

Figure:Competingmodelsfortheevolutionofmorphologicaldisparity-from[4]

competitionandmassextinctionevents).Theseputativedriversandlimitswillbeexaminedinturnandincombinationtodeterminewhethertheyyieldthepatternsofdesignspaceoccupationthatareobservedinrealclades.Thecandidatewillalsoexplorehowthestructuralandphylogeneticrelationshipsamongcharacterscontributestomorphospaceoccupation.WhiletheintentionistosamplebroadlyacrossorganismaldiversityandthroughoutthePhanerozoic.thereisalsoscopetofocusonparticulargroups,dependinguponthesuccessfulcandidate’sinterest.Ultimately,theresultsofthesimulationstudieswillidentifytherelativerolesofdifferentevolutionaryprocessesinshapingtheoccupationofdesignspace,andprovideanewtheoreticalframeworkwithinwhichtoevaluatetheresultsofempiricaldisparityanalyses.Theywillalsospeaktoaseminalcontroversyinmacroevolution,namelytheuniformitarian/non-uniformitariandebate.References1. D.H.Erwin,Disparity:morphologicpatternanddevelopmentalcontext.Palaeontology50,57-73(2007).2. D.H.Erwin,Evolutionaryuniformitarianism.Developmentalbiology357,27-34(2011).3. J.E.O'Reillyetal.,Bayesianmethodsoutperformparsimonybutattheexpenseofprecisionintheestimationofphylogenyfromdiscretemorphologicaldata.BiologyLetters12,20160081(2016).4. J.W.Oyston,M.Hughes,S.Gerber,M.A.Wills,Whyshouldweinvestigatethemorphologicaldisparityofplantclades?Annalsofbotany,(2015).