Few amphibians from the Chugoku District, including Chugoku Mountains (western Honshu, Japan), have been the focus of taxonomic attention. However, recent studies using molecular phylogenetic approaches have revealed that this region is a center of speciation for some amphibian species. The region is particularly important for the speciation of a salamander, Hynobius nebulosus. This species normally inhabits lowlands, but in the Chugoku Mountains, it has invaded montane regions and acquired unique ecological and morphological traits. Other salamanders show unusual traits, including H. naevius, which is morphologically highly variable, and H. kimurae which has extremely large body sizes in this region. Morphological variations found in these species in the Chugoku Mountains seem to be affected by their ecological relationships. The Chugoku District, including Chugoku Mountains, is also regarded as a boundary between genetic groups of other amphibians including the newt, Cynops pyrrhogaster, toad, Bufo japonicus, and frog, Rhacophorus arboreus.
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