Data from: Unexpected pathway for intercontinental movement into the Nearctic revealed by phylogenetic analyses

Much of North America’s freshwater biodiversity is derived from Palearctic
lineages. Isopods of the Holarctic family Asellidae are among the most
widespread and diverse freshwater crustaceans, but Nearctic species are
poorly studied. We examined the evolutionary history of the family,
utilizing Sanger sequencing of mitochondrial and nuclear DNA, and both
Maximum-Likelihood and Bayesian Inference. The genera Calasellus
and Salmasellus from the western United States are shown to be basally
derived, suggesting they have only distant affinity to other Nearctic taxa
and represent relictual lineages taht likely diverged in the Jurassic.
Remaining Nearctic asellids formed a monophyletic group sister to the Lake
Baikal endemic genus Baikalasellus, which diverged during the Early
Cretaceous. Our results show a close connection between Nearctic and
eastern Palearctic asellids, with an Early Cretaceous divergence
consistent with limited connections between Asia and North America. We
propose that asellids used a Beringian route to colonize the Nearctic from
west to east, in contrast to Europe-to-North America routes hypothesized
for other freshwater crustaceans. Many of the genera we analyzed were
non-monophyletic; taxonomic revision may shed further light on the route
and timing of asellid diversification in the Nearctic and on the processes
by which freshwater taxa colonized this realm.