Wide Distribution but Low Differentiation: Phylogenetic Relationships and Phylogeography of Hynobius nigrescens (Amphibia: Caudata).

We surveyed the genetic structure of Hynobius nigrescens Stejneger, 1907, a lentic breeding salamander widespread throughout montane and lowland regions of northeastern Japan. We performed a mitochondrial DNA analysis to explore intraspecific genetic variation and infer the evolutionary population history of H. nigrescens. Complete 1141 bp sequences of the mitochondrial cytochrome b gene were studied for 134 adult and larval individuals collected from 62 localities, encompassing the known range of the species. Hynobius nigrescens proved to be monophyletic, including two major clades (Clade II from southwestern Hokuriku and Clade I from all other localities). The latter clade comprises four well-supported and geographically structured subclades, which show genetic distances smaller than those seen in the widely sympatric species Hynobius lichenatus. Results of population statistical analyses indicated that Clade II of the westernmost range of H. nigrescens seems to have maintained a constant population size, while Clade I from most of the northeastern species range shows a tendency of recent population expansion, which is evident in Subclades I-A from the northernmost range and I-B from southern Tohoku to northern Kanto and eastern Chubu. In contrast, Subclades I-C from northeastern Chubu and Sado Is. and I-D from northwestern Chubu to Hokuriku seem to have been relatively stable in population size. Hynobius nigrescens differs greatly from other salamander species from northeastern Japan in its much more recent periods of genetic differentiation and its pattern thereof, and is suggested to be a young faunal element in this region.

Mitochondrial cytochrome B phylogeny and historical biogeography of the Tohoku salamander, Hynobius lichenatus (Amphibia, Caudata).

The Tohoku salamander, Hynobius lichenatus Boulenger, 1883, is a lentic breeding species widespread throughout montane regions of northeastern Japan. To explore intraspecific genetic variation and infer evolutionary history of H. lichenatus, we performed mitochondrial DNA analysis (complete 1141 bp sequences of the mitochondrial cytochrome b gene) using 215 adult and larval individuals collected from 75 localities, encompassing known distributional range of the species. Hynobius lichenatus proved to be monophyletic, including three well-supported and geographically structured clades (Clade I from northern Kanto, Clade II from southern Tohoku, and Clade III from northern Tohoku). These clades, respectively, comprise several subclades, and show genetic distances as large as those seen between different species of Hynobius. Results of population statistic analyses indicate that all clades and most subclades have maintained high genetic diversity and demographic stability over long periods. Molecular dating indicates divergence in H. lichenatus concords with topographic evolution of northeastern Japan from late Miocene to early Pleistocene, suggesting that paleogeographic events in this region, such as orogenesis, sea level change, and volcanic activity, have been crucial for shaping genetic patterns and diversity in this species. Hynobius lichenatus greatly differs from many other animal species from northeastern Japan in its much older periods and the pattern of genetic differentiation, and is suggested as an old faunal element in this region.