Phylogene)cinves)ga)onoftheBaikalodrilusspeciesflock(Clitellata,Naididae)endemictoLakeBaikal,SiberiaPatrickMar)n1,GontranSonet2,NathalieSmitz3,SophieGombeer4,ThierryBackeljau1,2,4,5

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AbstractBackground:LakeBaikalisthedeepestandmostvoluminouslakeintheworld,withauniqueenvironment(ultraoligotrophicandwell-oxygenatedwatersatalldepths),andislocatedinaregionthatisexperiencingrapidclimatechange.Itispopulatedwithanendemicgenusofoligochaetes(Baikalodrilus),whichcurrentlycomprises21morphospecies.However,thevalidityofmanyspeciesisques)onable;thegreatsimilarityintheirdescrip)onandthelackofunequivocaldiagnos)ccharactersoTenleadspeciesiden)fica)ontoanimpasse.Inordertoclarifythesystema)csofthisgenus,weanalysedonenuclear(ITS)andtwomitochondrial(COIand16S)markersof33BaikalodrilusspecimensandfourspecimensofthegeneraSpirosperma,Embolocephalus,RhyacodrilusandHaberasanoutgroup.Results:Phylogene)cinferencesbasedonparsimony,maximumlikelihoodandBayesiananalysesshowedanearlysepara)onbetweentwogroupsofspeciesthatbelongtotwodis)nctsizeclassesandhelpedtore-evaluatethevalidityofsomemorphologicalcharactersasspecificdiagnos)ccharacters.Threespeciesiden)fiedpriortomolecularanalyseswereconsistentwithclusteringbasedonDNAsequences.Afourthmorphospeciesprovedtobeactuallyanassemblageoftwodis)nctspecies.Itwasalsopossibletoisolateagroupofspecimensthatcouldbeconsideredasanewspecies.Otherclustersremainedambiguous,notonlyintermsofmolecularclusteringbutalsoofmorphologicaldis)nctness.Significance:Theseresultswillbeusefulforataxonomicalrevisionofthegenusandabe[erassessmentoftheoligochaetespeciesdiversityinalakeenvironmentfacingcontemporaryclima)cchanges.

TheBaikalodrilusspeciesflockBaikalodrilusisanendemicgenusofoligochaetestoLakeBaikal,whichcurrentlycomprises21morphospecies.Byitsmonophyly,endemicity,andspeciosity,thegenuscanbeconsideredasa“speciesflock”.However,thevalidityofmanyspeciesisques)onable;thegreatsimilarityintheirdescrip)onandthelackofunequivocaldiagnos)ccharactersoTenleadspeciesiden)fica)ontoanimpasse.

Evolu=onaryhistoryPhylogene)cinferencesshowedanearlysepara)onbetweentwogroupsofspeciesthatbelongtotwodis)nctsizeclasses(seeB.digitatusandB.werestschaginivs.allothers).Thegene)cvariabilitywithintheflockislow,sugges)nga“recent”radia)onofBaikalodrilus,possiblycontemporarywithdrama)cclima)cchangesinBaikalenvironmentthatoccurredatthebeginningofthePleistocene(±2Mya).

Phylogene=cinferencesInordertoclarifythesystema)csofthisgenus,phylogene)canalyseswerecarriedoutusingonenuclear(ITS)andtwomitochondrial(COIand16S)markers,andcomplementaryphylogene)creconstruc)onsmethods(parsimony,maximumlikelihoodandBayesiananalyses).Thethreemethodsgavecongruentresults.

Speciesdelinea=onThreespeciesiden)fiedpriortomolecularanalyseswereconsistentwithclusteringbasedonDNAsequences.Afourthmorphospeciesprovedtobeactuallyanassemblageoftwodis)nctspecies.Itwasalsopossibletoisolateagroupofspecimensthatcouldbeconsideredasanewspecies.Otherclustersremainedambiguous,notonlyintermsofmolecularclusteringbutalsoofmorphologicaldis)nctness.Morphologicalcharactersprovedtobeofvariableusefulnessasspeciesdiagnos)ccharacters.Ataxonomicalrevisionisbadlyneededbutmosttypesareseeminglylost…sothatthevalidityofmanyspeciesisqueried(speciesinquirenda).

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LakeBaikalisthedeepest(1,637m),themostvoluminous(23,000km3)andthemostancient(25–30Myr)lakeintheworld,withauniqueenvironment(ultra-oligotrophicandwell-oxygenatedwatersatalldepths).Itislocatedinaregionthatisexperiencingrapidclimatechange.Thelakeharboursabout192oligochaetespecies,ofwhichmorethan70%areendemicandspeciesflocksarerecognizableorsuspected.

Auniqueenvironmentfacingcontemporaryclima=cchanges

FIGURE1:Phylogene)ctreebasedontheconcatena)onofCOI,16Sand18S-ITS1-5.8S-ITS2-28Sandreconstructedusingthemaximumlikelihoodmethodwith1000bootstrappseudoreplicates.

100.0

PA0905102-Papillate juvenile

EY0805112-Embolocephalus yamaguchii

0228503-Embolocephalus nikolskyi

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86

86

49

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100

49

60

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100

47

63

87

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93

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67

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0016502

0028505-B_discolor

0034602

0034604

0107604

0035004-B_digitatus

0103608-B_discolor

0033401-B_malevici

0103601-B_werestschagini

0106502

0107606-B_discolor

0103609

0107608

0016104

0028502-B_cf_digitatus

0107603

0033402

0034605-B_digitatus

0131206

0031307

0107609

0028501-B_werestschagini

0106509

0107607

0034601-B_discolor

0034603

0103603

0106504

0103606-B_malevici

0107602

0016101

0107601

0107605

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Affilia)ons1  TaxonomyandPhylogeny,RoyalBelgianInsEtuteofNaturalSciences,rueVauEer29,

1000Brussels,Belgium2  JEMU,RoyalBelgianInsEtuteofNaturalSciences,rueVauEer29,1000Brussels,Belgium3  JEMU/BopCo,RoyalMuseumofCentralAfrica,Leuvensesteenweg11-17,3080Tervuren,

Belgium4  BopCo,RoyalBelgianInsEtuteofNaturalSciences,rueVauEer29,1000Brussels,Belgium5  EvoluEonaryEcologyGroup,UniversityofAntwerp,Groenenborgerlaan171,2020Antwerp,

Belgium

FIGURE2:Loca)onwhereindividualsweresampled.Colourcodesareusedinordertomatchloca)onsandhighlightedclustersofFig.1