The origin and population divergence of Parabotia curtus (Botiidae: Cypriniformes), a relict loach in Japan

Parabotia curtus is the only botiid species in Japan, where its range is restricted to two small regions, Kinki and Sanyo. In this study, we performed molecular phylogenetic and population genetic analyses to reconstruct the evolutionary history of this species. A time tree constructed based on mitochondrial genome data revealed that P . curtus was one of the earliest species derived from the most northward range-expanding botiid group ( Parabotia ) during the Late Miocene. A reduction in its distribution and population size during the Late Pleistocene was inferred from shallow but clear regional population divergence, as verified by mitochondrial sequence and microsatellite data. These results provide evidence that this species is a relict of an old layer of Japanese freshwater ichthyofauna and emphasize the need to conserve the Kinki and Sanyo populations as distinct evolutionary units.