Systematics And Biogeography Of The Primitively Segmented Spiders,Liphistiidae (Araneae:Mesothelae)

The primitively segmented spider family Liphistiidae(Araneae:Mesothelae)is a species-poor and ancient lineage containing species with restricted,disjunct geographical distributions confined to Southeast and East Asia.Liphistiids are widely recognized as "living fossils"among spiders since they have retained plesiomorphic arachnid traits such as the abdominal tergites and spinnerets located in the middle of abdominal venter.Moreover,their sedentary,slow and cryptic life history may preclude their colonization ability,making them poor dispersers.Due to their antiquity,high level of endemism,disjunct distribution,and poor dispersal ability,liphistiids are important for the study of spider tree of life,including insights of spider origin and evolutionary history,as well as for testing biogeographic hypotheses as they relate to plate tectonics,dispersal routes,and physical barriers to speciation.However,the acute absence of a liphistiid molecular phylogeny has so far prevented testing any evolutionary and biogeographic hypotheses.The overall aim of the thesis is therefore to use molecular data to explore the phylogenetic relationships and to clarify the systematics of the family Liphistiidae with a focus on the subfamily Heptathelinae.Specifically,I aim to:(1)provide the first species level phylogeny of liphistiids using original molecular data,and thereby testing the monophyly of the family and genera;(2)investigate the origin,divergence times,dispersal route,and historical biogeography of liphistiids,as well as test the role of plate tectonics and potential geographical barriers for speciation;(3)integrate the molecular phylogeny,genetic data and morphological characters to complete a taxonomic revision of the family;and(4)study phylogeography and population genetics of East Asian margin(EAM)island liphistiid genera and species.1776 specimens at 167 localities were sampled,primarily with focus on East Asia to amplify and sequence five genes(two mitochondrial genes:cytochrome c oxidase subunit 1(CO1)and 16S rRNA,and three nuclear loci:28S rRNA,histone 3(H3)and internal transcribed spacer 2(ITS2)).Using these molecular data,I first performed maximum likelihood(ML),maximum parsimony(MP)and Bayesian analyses(BI)under four partition schemes to reconstruct the phylogeny of liphistiids and to test the monophyly of the family and genera.The extensive field work over their present range discovered numerous new localities and species and,albeit emphasizing heptathelines,secured a taxon sample needed for the first comprehensive species level phylogeny of Liphistiidae.This phylogeny strongly supports the monophyly of Liphistiidae and of eight genera,which contain six known and two new genera(Ganthela gen.nov.,Heptathela,Liphistius,Qiongthela gen.nov.,Ryuthela,Sinothela,Songthela,Vinathela),thus rejecting the current three-genus classification of the family.I also performed dating analyses and ancestral distribution reconstruction to estimate the divergence times,reconstruct the biogeographic history of the family,genera and species.While extant liphistiids indeed possess arachnid plesiomorphies not shared with any other spiders,and the Mesothelae lineage traces back as far as the late Permian,my analyses uncover that their origin and diversification are surprisingly much more recent than once thought,repeating the patterns recently detected also in other textbook living fossils.I traced the origin of the family in Southeast or East Asia to the late Paleogene and Eocene(39-58 Ma),and the origins of all eight genera to the late Oligocene and Neogene.However,I found that liphistiids do belong to a very long evolutionary branch that connects them with the only mesothelean fossil known from Eurasia,and consequently,some of their phenotypic traits resemble the hypothetically ancestral spiders.With these analyses,I tested three alternative hypotheses of the origin of Liphistiidae:i)'Out of Gondwana' hypothesis,ii)'Stepping-on Middle East' hypothesis,and iii)'Silk road' hypothesis.Interestingly,the reconstructed ancestral areas and dispersal versus vicariant events do not require any explanations of over water dispersal in liphistiid biogeographic history.Apparently,effective water barriers include not only bodies of ocean,but also major rivers,notably Yangtze.To resolve the taxonomy of the new genus Ganthela,I employed five species delimitation methods(DNA barcoding gap,species delimitation plugin(P ID(Liberal)),automatic barcode gap discovery(ABGD),generalized mixed Yule-coalescent model(GMYC),and statistics parsimony(SP))based on the single-locus COl.My results reveal that DNA barcoding gap,P ID(Liberal),and ABGD agree with morphology,while GMYC and SP indicate several additional species.I used the consensus results to delimit and diagnose six Ganthela species:one known species:G.cipingensis(Wang,1989)and five new described species:G.jianensis,G.qingyuanensis,G.wangjianensis,G.xianyouensis,and G.venus,which in addition to the type G.yundingensis Xu,2015,completes the genus revision.These results indicate that even single-locus analyses based on CO1 barcode,if integrated with morphological and geographical data,provide sufficiently reliable species delimitation for sessile and range restricted spiders.Finally,I investigated phylogeography,population genetic structures and demographic history of the two liphistiids genera inhabiting the EAM(Heptathela and Ryuthela)using COl data.The dating analyses suggest that i)the clade Heptathela + Ryuthela originated well before the EAM islands became separated from the continent;ii)the ages of Ryuthela and Heptathela coincide with the opening of Japan Sea and the formation of the Ryukyu Trench;iii)a clade within Ryuthela coincides with the opening of the Kerama Gap;iv)species of Ryuthela and Heptathela are relatively young.Population genetics and demographic results suggest interrupted gene flow within and among the islands,strong population differentiation among and within populations,and most species exhibiting stable past populations.In sum,my thesis provides the first time-calibrated phylogeny of the primitively segmented spider family Liphistiidae and EAM island liphistiid spiders.The results do not support the current three-genus classification of liphistiids,but instead suggest eight genera in two subfamilies.Fossil evidence and calibration dating analyses show that the lineage traces back as far as the late Carboniferous and the early Permian,and postulate a long eastward over-land dispersal towards Asia.Their origin and diversification are surprisingly much more recent than once thought.Restricted gene flow and geographical barriers may have shaped their current-day disjunct geographical distributions.Both the reconstructed biogeographic history of Liphistiidae and their natural history namely suggest that these spiders are very poor and slow dispersers that,rather than ever move over water or over short lived land bridges,prefer to maintain their restricted ranges,or ride vicariantly on drifting continents.Because of their ancient origins and limited dispersal abilities,liphistiids retain their genetic imprint and biogeographic signal,and should thus join other ancient litter or soil dwelling arthropods as excellent models for biogeographic research.