Download Morphological disparity

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).