Flightless beetles crossed the Pacific Ocean: phylogeny and biogeography of the intertidal genus Diaulota Casey (Coleoptera: Staphylinidae: Aleocharinae)

The North Pacific distribution of coastal staphylinids may be explained as the result of either dispersal or vicariance. The intertidal rove beetle genus Diaulota is a submarine group that occurs on the Pacific coasts of the Northern Hemisphere. We performed a phylogenetic analysis of Diaulota using molecular characters (3241 bp) to investigate their biogeographic history and patterns. The data were analysed by parsimony, Bayesian, and maximum likelihood methods. Model-based analyses showed the same pattern of Diaulota species relationships, but parsimony analysis resulted in different species relationships for the unresolved clade B. Biogeographical analyses suggested that the common ancestor of Diaulota occurred widely along the East Asian coast with repeated dispersal to the north-eastern Pacific from the north-western Pacific. According to the reconstruction of the ancestral areas, both dispersal (seven events) and vicariance (four events) were important in shaping its current distribution. Although most species underwent stepwise colonization from East Asia via Kamchatka and Alaska to North America along the coast, a single lineage (Diaulota fulviventris and Diaulota harteri) crossed the Pacific Ocean directly from the north-western Pacific to the north-eastern Pacific, possibly via sea surface currents.