Deep history of an ancient subterranean crustacean: origins of the Bathynellacea ( Syncarida )

Abstract

Plate-tectonic-mediated vicariance is often invoked to explain global disjunct distributions. However, since the advent of molecular tools, particularly molecular dating, it has become apparent that in many of the taxa, dispersal post-continental break-up better explains their current distribution. Nevertheless, these taxa belong to younger radiations and are less suitable for deep-time biogeographic studies. Here, we target an ancient lineage of subterranean freshwater crustacean of the order Bathynellacea with limited dispersal ability and global distributions to investigate the role of plate-tectonic-mediated vicariance. We investigated the evolutionary relationships among bathynellaceans using phylogenetic analyses of nuclear and mitochondrial markers. For the first time, four outgroup fossils were used to calibrate the time tree to date the origin and significant diversification events of bathynellaceans. Our results reveal deep phylogenetic divergences among Bathynellacean families, suggesting an ancient origin dating back to the Mesozoic or possibly even the Late Palaeozoic. The early branching lineages are geographically distributed across former Gondwanan landmasses and Eurasia, supporting a dual origin scenario and challenging previous views of a single Laurasian ancestry. The taxonomic implications of our phylogeny are also discussed. Overall, this study demonstrates Bathynellacea as a valuable model for understanding deep-time evolutionary processes.