Extant primitively segmented spiders have recently diversified from an ancient lineage

Abstract

Living fossils are lineages that have retained plesiomorphic traits through long time periods. It is expected that such lineages have both originated and diversified long ago. Such expectations have recently been challenged in some textbook examples of living fossils, notably in extant cycads and coelacanths. Using a phylogenetic approach, we tested the patterns of the origin and diversification of liphistiid spiders, a clade of spiders considered to be living fossils due to their retention of arachnid plesiomorphies and their exclusive grouping in Mesothelae, an ancient clade sister to all modern spiders. Facilitated by original sampling throughout their Asian range, we here provide the phylogenetic framework necessary for reconstructing liphistiid biogeographic history. All phylogenetic analyses support the monophyly of Liphistiidae and of eight genera. As the fossil evidence supports a Carboniferous Euramerican origin of Mesothelae, our dating analyses postulate a long eastward over-land dispersal towards the Asian origin of Liphistiidae during the Palaeogene (39-58 Ma). Contrary to expectations, diversification within extant liphistiid genera is relatively recent, in the Neogene and Late Palaeogene (4-24 Ma). While no over-water dispersal events are needed to explain their evolutionary history, the history of liphistiid spiders has the potential to play prominently in vicariant biogeographic studies.

A genus-level taxonomic review of primitively segmented spiders (Mesothelae, Liphistiidae)

“…These vouchers, deposited at the Centre for Behavioural Ecology and Evolution (CBEE), College of Life Sciences, Hubei University, Wuhan, China, were the basis for our morphological examinations (reported here) and for molecular analyses (Xu et al submitted). Examined and illustrated specimens were labelled with unique codes (Appendix 1; see also Figure legends), which will be reused in the upcoming genus-level revisions.…”

“…In a concurrent paper (Xu et al submitted), we report on phylogenetic analyses using original five-gene nucleotide data for 75 species. These results, summarized in Figure 2, form the phylogenetic basis for a revised classification of the family.…”

“…Despite being large and morphologically distinct, they are rarely encountered, making it difficult to secure taxonomically meaningful samples. Their natural history also suggests that liphistiids are confined to their burrows and that the spiders rarely move around, and phylogenetic and biogeographic analyses confirm that they are dispersal-limited and highly genetically structured (Xu et al submitted). …”

“…In a sister paper (Xu et al submitted), we used molecular data from our original extensive sampling to test the monophyly of the family Liphistiidae and the genera within. Based on a species-level multi-locus phylogeny reported in that paper, and on morphological and natural history diagnostic characters provided here, we revise below the higher level systematics of the family.…”

Two new species of the purse-web spider genus Atypus Latreille, 1804 from Hainan Island, China (Araneae, Atypidae)

“…All molecular procedures on extraction, amplification and sequencing followed standard protocols (see Xu et al 2015). …”