A barcode-based phylogenetic scaffold for Xysticus and its relatives (Araneae: Thomisidae: Coriarachnini)

Abstract

The phylogenetic relationships and taxonomy of the crab spider genus Xysticus and its closest relatives (i.e., the tribe Coriarachnini, also including, e.g., Ozyptila, Coriarachne and Bassaniana) have long been controversial, with several alternative classifications being proposed, none of which has gained universal acceptance. As Coriarachnini is largely confined to the Holarctic region, the main target area of recent DNA barcoding projects for spiders, a large amount of genetic data for the group is now publicly available. The results of a phylogenetic analysis of this sequence dataset are largely congruent with earlier morphology-based results regarding the evolutionary structure of the group. In particular, they highlight the fact that Xysticus s. lat. is a paraphyletic assembly and that several species groups need to be placed in separate genera to achieve monophyly of Xysticus s. str. Similarly, Coriarachne and Bassaniana appear as independent clades rather than a joined monophyletic Coriarachne s. lat. In contrast, further subdivision of Ozyptila is not supported by the genetic data. Importantly, the analysis also shows that anapophysate members of Xysticus s. lat. form two widely separated groups: a primarily anapophysate division, also including Coriarachne and Bassaniana, at the base of Xysticus s. lat., and a secondarily anapophysate clade deeply nested within Xysticus s. str. This might explain some of the earlier difficulties when trying to define generally accepted subgroups within Xysticus s. lat. The phylogenetic scaffold based on barcode sequences is sufficiently dense and well resolved to attempt the tentative and provisional placement of the majority of species in Xysticus s. lat. in the independent genera Xysticus s. str., Bassaniodes, Psammitis and Spiracme as a starting point for a future more formal revision of the group.