Beringian Freshwater Mussel Beringiana beringiana (Unionidae) in Northeast Asia

Abstract

The origin of the fauna of Beringia is a notable biogeographical puzzle. Large mussels of the genus Beringiana inhabit both Northeast Asia and the northwestern part of North America and thus provide an important model to investigate the paleobiogeography of Beringia and the past and current intercontinental species exchanges. Data on Beringiana distribution, morphology, genetics, and taxonomy are fragmentary or questionable. In this study, we summarized the data on its distribution in Northeast Asia, performed genetic analysis (cox1), and studied the variation in the shell morphology in samples from four isolated populations, including the putative sympatric species. Over ten large enclaves of Beringiana are currently known in Northeast Asia (east to the Verkhoyansk Range), mostly in the lower reaches of large rivers in northeastern Yakutia, Kamchatka, Magadan Oblast, and Khabarovsk Krai. These enclaves are far apart (several hundreds of kilometers) because the mussel is associated with muddy sand or pebbly sand bottom substrates and spreads through its glochidia, which are parasitic on the fish. Shell morphology can be highly variable even in a single population, overlapping the diagnoses of several Beringiana species (which are currently not recognized as valid). Our analysis of the cox1 sequence in four populations identified all individuals as B. beringiana. We evaluated the possible current and probable Late Pleistocene–Early Holocene freshwater and marine pathways of B. beringiana dispersal through the area of former Beringia, including the current intercontinental migration of glochidia on fish.