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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55N
110E
105E
00.285.0201.036.0100.285.01
00.350.0400.346.05
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±0 100 20050Kilometers
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bathymetry (250 m interval)
orography (500 m interval)
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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
73
86
86
49
100
85
100
49
60
100
100
47
63
87
47
93
97
83
100
50
100
100
67
84
100
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
100
60
86
97
100
100
95
42
40
81
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
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