Taxonomic reassessment of salamanders (genus Hynobius) from Tsushima Islands, Japan, with a resurrection of Hynobius tagoi Dunn, 1923 (Amphibia: Caudata).

To clarify the taxonomic status of salamanders from Tsushima Islands, Japan, we examined two species of salamanders, Hynobius tsuensis and Hynobius sp. from Tsushima Islands, and compared them with H. nebulosus from Kyushu. We found that the three taxa differ from each other in nuclear DNA, adult morphology, and egg-sac shape, and consider them to be independent species. Based on the investigation of type specimens of the synonyms, we identified Hynobius sp. as H. tagoi Dunn, 1923 and redescribe it herein. Also, we designate a neotype for H. tsuensis and redescribe H. tsuensis. The distribution areas of the two species partly overlap but they were distinguishable by their body colorations: H. tsuensis has uniformly blackish tail sides and a distinct yellow stripe on the upper tail edge; whereas H. tagoi has brown tail sides with numerous dark stippling and without a distinct yellow stripe on the upper tail edge.

Differentiated historical demography and ecological niche forming present distribution and genetic structure in coexisting two salamanders (Amphibia, Urodela, Hynobiidae) in a small island, Japan.

Background: The climatic oscillations in the Quaternary period considerably shaped the distribution and population genetic structure of organisms. Studies on the historical dynamics of distribution and demography not only reflect the current geographic distribution but also allow us to understand the adaption and genetic differentiation of species. However, the process and factors affecting the present distribution and genetic structure of many taxa are still poorly understood, especially for endemic organisms to small islands. Methods: Here, we integrated population genetic and ecological niche modelling approaches to investigate the historical distribution and demographic dynamics of two co-existing salamanders on Tsushima Island, Japan: the true H. tsuensis (Group A), and Hynobius sp. (Group B). We also examined the hypothesis on the equivalency and similarity of niches of these groups by identity and background tests for ecological niche space. Results: Our result showed that Group A is considered to have undergone a recent population expansion after the Last Glacial Maximum while it is unlikely to have occurred in Group B. The highest suitability was predicted for Group A in southern Tsushima Island, whereas the northern part of Tsushima Island was the potential distribution of Group B. The results also suggested a restricted range of both salamanders during the Last Interglacial and Last Glacial Maximum, and recent expansion in Mid-Holocene. The genetic landscape-shape interpolation analysis and historical suitable area of ecological niche modelling were consistent, and suggested refugia used during glacial ages in southern part for Group A, and in northern part of Tsushima Island for Group B. Additionally, we found evidence of nonequivalence for the ecological niche of the two groups of the salamanders, although our test could not show either niche divergence or conservatism based on the background tests. The environmental predictors affecting the potential distribution of each group also showed distinctiveness, leading to differences in selecting suitable areas. Finally, the combination of population genetics and ecological modeling has revealed the differential demographic/historical response between coexisting two salamanders on a small island.

Discovery of Two Lineages of Hynobius tsuensis (Amphibia, Caudata) Endemic to Tsushima Island, Japan.

The Tsushima salamander, Hynobius tsuensis, is a lotic-breeding species endemic to Tsushima Island, Japan. We investigated genetic variation in this species using samples covering all known localities on the island. Phylogenetic analyses based on mitochondrial cytochrome b gene sequences divided H. tsuensis populations into two genetic groups: true H. tsuensis and an unknown species (Hynobius sp.) showing a closer relationship to Hynobius nebulosus than to H. tsuensis. The genetic distance between the two groups was greater than the genetic distances between different species of Hynobius. Both groups were found to breed in mountain streams, sometimes in the same streams syntopically. Population structure analysis based on several nuclear microsatellite loci strongly indicated reproductive isolation between the two groups in the syntopic localities. This is the first report confirming the syntopic occurrence of two lotic salamanders of Hynobius on a small island. We propose that the lotic breeding habits of the two salamanders were independently acquired.