Phylogenetic relationships and biogeography of the Japanese clawed salamander, Onychodactylus japonicus (Amphibia: Caudata: Hynobiidae), and its congener inferred from the mitochondrial cytochrome b gene

Using the mitochondrial cytochrome b gene, we investigated phylogenetic relationships between and within the Japanese clawed salamander, Onychodactylus japonicus, and its close continental relative O. fischeri. Monophyly of O. japonicus was well supported, and O. japonicus was clearly distinguished from O. fischeri. However, O. fischeri comprises genetically distinct populations from Russia, NE China, and Korea that do not form a monophyletic group. Within O. japonicus, four major clades were clearly recognized: Clade I from northern Tohoku district, Clade II from southern Tohoku district and the Tsukuba Mountains, Clade III from southwestern Honshu, and Clade IV from Kinki and Chugoku districts in Honshu and from Shikoku. Although genetic distances among these clades were large (5.5–9.6%), relationships among the clades were unresolved. All clades except Clade I contained two or three distinct subclades. In several localities in Kinki and Chugoku, Clades III and IV were sympatric. The estimated divergence times and available geohistorical data suggest that O. japonicus began to differentiate in the Upper Late Miocene and that the pattern of genetic differentiation of this species has been affected strongly by climate changes and geohistorical events such as volcanic activity and mountain formation. Our results suggest that both O. fischeri and O. japonicus comprise multiple cryptic species.