A freshwater mussel species reflects a Miocene stream capture between the Mekong Basin and East Asian rivers

Freshwater mussels belonging to the genus Cristaria Schumacher, 1817 (Bivalvia: Unionidae) are widespread from Mongolia to Indochina while the range of one species, C. plicata (Leach, 1814), covers two biogeographic subregions, i.e., East Asian (Amur River to Vietnam) and Sundaland (Mekong River basin). We present here a taxonomic revision of the nominal taxon Anodonta bellua Morelet, 1866 which was described from the Mekong (Lake Tonle-Sap, Cambodia) but is currently considered a synonym of C. plicata. We obtained molecular data for newly collected Cristaria representatives from the Mekong's tributaries in Laos, which were found as a divergent species-level phylogenetic clade within the genus that is distant from C. plicata. Nevertheless, comparative morphological and morphometric studies did not reveal any significant differences between these two congeners. Our time-calibrated biogeographic modeling reveals that the split between Cristaria bellua (Mekong) and C. clessini (East Asia) probably occurred in the mid-Miocene (15.8 Ma) and may reflect an ancient stream capture between the Mekong Basin and East Asian rivers.