Phylogeography of the bitterling Tanakia lanceolata (Teleostei: Cyprinidae) in Japan inferred from mitochondrial cytochrome b gene sequences

The bitterling Tanakia lanceolata is a primary freshwater fish with wide distribution range in Japan; therefore, analysis of this species will yield much information on the formation of Japanese freshwater fish fauna. However, populations of this species are threatened by several human activities. To reveal the genetic population structure of T. lanceolata and the process of its formation, as well as its genetic status, we conducted phylogenetic analyses and estimated divergence times based on partial sequences of the mitochondrial DNA cytochrome b gene, using specimens collected across the distribution range. The results of the analysis showed that Japanese T. lanceolata is monophyletic and consists of seven local population groups that diverged from the Late Pliocene to the Middle Pleistocene. The population structure in western Japan was similar to that of other freshwater fishes (e.g., separation by the Suzuka Mountains), although there were several differences in population boundaries and the presence/absence of a secondary contact zone. The Central Highlands in central Honshu are the primary, or at least the most effective, geological barrier responsible for population divergence in Japanese freshwater fish species. However, the small genetic differentiation of the T. lanceolata population between the western and eastern sides of the Central Highlands suggested recent dispersal and gene flow across the region after uplift of the highlands. The genetic population structure indicated extensive genetic disturbance in the Kanto Region. Our results provide information on the formation process of the Japanese freshwater fish fauna, which could aid conservation efforts toward T. lanceolata.