组会刘媛文献精讲

Geneflowandnaturalselectionshapespatialpatternsofgenesintreepopulations:implicationsforevolutionaryprocessesandapplicationsVictoriaL.SorkAbstractAcentralquestioninevolutionarybiologyishowgeneflowandnaturalselectionshapegeographicpatternsofgenotypicandphenotypicvariation.First,throughstudiesofcontemporarypollenandseedmovement,Sorkhasstudiedhowlimitedgenemovementcreatesfine-scalegeneticstructure,whilelong-distancegeneflowpromotesconnectivity.Second,Sorkresearchonspatialpatternsofgeneticvariationhasinvestigatedtheinteractingimpactsofgeographyandclimateongeneflowandselection.Third,usingnext-generationgenomictools,sheisnowstudyinggeneticvariationonthelandscapetofindinitialevidenceofclimate-associatedlocaladaptationandepigeneticvariationtoexploreitsroleinplantresponsetotheclimate.

IntroductionOverthelasttwentyplusyears,herresearchhasfocusedongeneflowandgeographicalpatternsofgeneticvariationatdifferenttemporalandspatialscales.1.Geneflowandnaturalselectionaretwocentral.Usuallyopposing,evolutionaryforces:geneflowdistributes,homogenizes,andmaintainsgeneticvariationthatcanactasthe‘stuffofevolution’,whilenaturalselection

reducesgeneticvariationtothevariantsthatfavorsurvivalandreproduction.2.Howthedynamicsofgenemovementcreategeneticstructure？

Analyzecontemporarygenemovementthroughpollenandseeds.Numerousstudieshaveusedpaternity（亲本分析）analysistoassessthedistanceofpollen-mediatedgenedispersalandtheshapeofthedispersalkernel.Thisresearchhasgeneratedempiricaldataandnewmethodstoaddresskeyconceptsthroughthreelinesofinquiry:1

Contemporarygeneflowatalandscapescale.

2Geographicpatternsofgeneticvariation.3Landscapegenomicsofadaptivegeneticvariation.IntroductionFigure1(A)PhotoofadultQuercuslobataNee.(B)Landscapeviewoftypicaloaksavanna（稀树草原）habitatwithscatteredlargetreesofQ.lobata(leaflesscanopies)andQ.agrifolia(greencanopies).Backgroundandinitialdrivers1、Whethergeneflowwouldswampadaptivedivergence？Althoughwecannotruleoutmaternaleffectsorotherfactors,thesestrongphenotypicdifferencesonascalelessthanafewhundredmetersindicatethelocalselectionpressuresintreepopulationscouldbesufficientlyintensetoovercomegeneflow,orgenemovementissufficientlyrestrictedthatadaptationcanevolveonalocalscale.2、Impactoflandscapealterationongeneticdiversityofforesttreespecies?（景观改造）Givenevidencethatlandscapefragmentation(破碎)andreductionsinpopulationsizecouldjeopardize（危及）geneflowandconnectivity.Incontrasttotheotherstudiesthatlookedatimmediateimpactsofforest-cuttingpracticesoninsect,bird,andmammalbiodiversity,becauseofthelongevityoftrees,ourprojectwouldnotbeabletomeasurechangesindiversityforatleast50years.Instead,wechosetoinvestigatetheimpactsoncontemporarypollenflowbecauseanychangesingeneflowatthepresenttimewouldshapefuturediversity.ContemporarygeneflowintreesatalandscapescaleIfgeneflowisimpededbylandscapechanges,thenapopulationbecomesisolatedandcandecreaseineffectivesize,whichincreasesriskofinbreedingdepressionandlossofadaptivegeneticvariationthroughdrift.Geneflowwillpromotegeneticdiversitywithinlocalpopulationsandconnectivityamongpopulations.WeeventuallyfocusedourstudiesonthepollenandseeddispersalvectorsofCaliforniapopulationsofvalleyoak,Quercuslobata(Fig.3).Figure3Stagesofplantreproductionofwind-pollinatedandanimal-dispersedQuercuslobatainvolvedingeneflow.Pollenmovement

Pollenmovementinoaksisresponsibleformaintainingconnectivityamongpopulations,yetlocalpollinationissufficientlyfrequentthatitispossibletocreatefine-scalegeneticstructurethatcouldfacilitatelocaladaptation.

Formosttreepopulations,geneflowoccursprimarilythroughpollen.

pollenpooleffectivenumberofpollendonorslong-distancegeneflowriskofgeneticdriftlocaladaptationconservationstrategiesSeedmovementatalandscapescale

Seeddispersalismorelikelytoberestricted,soitaccountsformuchmoreofthefine-scalegeneticstructurethandoeslocalpollenmovement.Dispersalagents,suchaswesternscrubjays(灌丛鸦),facilitatelong-distanceacornmovementthatwouldallowcolonizationofnewsites,butbecausetheyvisitfewtrees,thegeneticdiversityofpatchyseedlingpopulationsisreducedduringthisphasefromthatintroducedthroughpollendispersal.

Formanytreespeciesisthatlocalizedgenemovementofpollenandseedswillcreatesufficientgeneticstructuretoallowtheevolutionoflocaladaptation,whilelong-distancegeneflowwillmaintainhighlevelsofgeneticdiversityandspreadfavorableallelesoverlargespatialscales.GeographicpatternsofgeneticvariationGeographicalpatternsofgeneticvariation:

(1)demographichistoryofpopulationexpansionandcontraction(2)migrationhistory(3)naturalselectionbothspatiallyandtemporally1.SpatialautocorrelationThesimplestformofspatialanalysisofgeneticvariationistoexaminethescaleofspatialautocorrelationofalleles.Mostplantpopulationsshowsomedegreeofspatialgeneticstructure(SGS),suggestingthisshortdistancegeneflowcreatesopportunityforthesurvivaloflocallyadaptedgeneticvariation.Geographicpatternsofgeneticvariation2.Geographicandenvironmentalassociationswithgeneticgradients(梯度)Whenaspeciesiswidelydistributed,itsevolutionaryhistorycanresultin：

geographicmosaic（镶嵌）ofgenotypesthatreflectsthemovementofgenes,theimpactofgeneticbottlenecks,andtheeffectsoflocalselectionpressures.Thisworkpredictsthatthelate21stcenturyclimateconditionscouldleadtoregionalextinctions（灭绝）formanyvalleyoakpopulationsunlesstheyhavepreexistingtoleranceforwarmer,drier,andmoreseasonalclimateenvironments.Infact,forsometreespecies,interventions,suchasassistedmigration,maybenecessary.3.Phylogeography:Phylogeographyisthestudyofgeographicpatternsofgeneticlineages（基因谱系）withthegoalofunderstandinghowthephysicallandscapeandclimatecyclesshapetheevolutionaryhistoryofspecies,theemergenceofnewspecies,andtheextinctionofothers.LandscapegenomicsofadaptivegeneticvariationHerjointlong-termgoalistounderstandthebasicevolutionarybiologyoflocaladaptionintreepopulations,particularlyinresponsetoclimate,andthegeneticcompositionoftreepopulationswillshapetheirresponsetoclimate.1.Climate-associatedcandidategenesIdentified40geneswhinfourfuncionalcategoriesforresponsetoclimatethatcouldbepotentialcandidatesunderselection.First,wefoundthatthetop5%ofFSTestimatesrangedfrom0.25to0.68,whilethemeanFST=0.03.Second,incorrelationanalysesofthe195single-nucleotidepolymorphisms(SNP)frequencieswithclimategradients,wefoundthreeSNPswithinbudburstandfloweringgenesandtwoSNPswithintemperaturestressgenesthatweresignificantlyassociatedwithmeanannualprecipitation(Fig.4).Theseanalysesrevealedthat10ofthe40candidategenesshowedevidenceofspatiallydivergentselection.Landscapegenomicsofadaptivegeneticvariation2.EpigeneticdifferentiationinvalleyoakEpigeneticvariationhasthepotentialtoshapephenotypicplasticity(表型可塑性)andadaptationtotheenvironment,eachofwhichcouldbeparticularlyimportantforthepersistenceoflong-livedorganismssuchastrees.ThispotentialisillustratedbystudiesofnaturalpopulationsofArabidopsis

thaliana（拟南芥）thatrevealpatternsofDNAmethylationwhichvaryacrossenvironmentsandmayprovideamechanismtoenhancetheadaptationtothelocalenvironment.ToassesswhethertheSNP(single-nucleotidepolymorphism)andSMP(singlemethylatedsitepolymorphism)variationdiffersacrosspopulations,wecalculatedpopulationdifferentiation,FST.Plattetal.(2015)foundthatmeanepigeneticdifferentiationamongthreepopulationsatvariablymethylatedCGsites(CG-SMPs)washigherthanthatbasedonSNPs(FST=0.28versusFST=0.19