<国立科博専報>対馬の爬虫両生類相小記

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The reptiles and amphibians of the Islands of Tsushima have repeatedly been studied by previous workers, because of their biogeographic importance as a stepping stone between the Korean Peninsula and West Japan. At least eighteen terrestrial and freshwater species of these animals have been recorded from these islands, but the number was reduced to twelve by GORIS (1965), who himself made a herpetological survey of the islands in the summer of 1965. Two of the twelve species, Bufo bufo japonicus and Rana catesbeiana, were proved to have been artificially introduced from West Japan, so that the number of the native species became ten according to his investigation. On the other hand, the occurrence of Rana chensinensis dybowskii and of Takydromus amurensis in the Tsushimas was subsequently reported by UEDA (1969) and SHIBATA (1966) respectively, and was confirmed by the zoolgists who participated in the collecting trips made in 1968 and 1969 as a part of the Natural History Research Project of the National Science Museum, Tokyo. No specimen of the other problematical species was obtained by the research project, their occurrence in the Tsushimas still remaining to be confirmed in the future. Thus, the number of the reptiles and amphibians native to the Islands of Tsushima amounts to twelve so far as we have confirmed up to the present. Their names are given at page 194 of the present articale. Of these, the four species, Hyla arborea japonica, Geoclemys reevesii, Gekko japonicus and Agkistrodon halys, occur both in the Korean Peninsula and in the Japanese main islands, and seem to have immigrated from the former into the latter through the ancient Tsushimas, with the exception of the gecko which no doubt invaded Tsushima from West Japan and then immigrated into Korea. The two species, Clemmys japonica and Elaphe climacophora, are endemic to the Japanese Islands and show little geographical variation. Their immigration into the Tsushimas seems to have taken place in rather a recent period, since there exists no perceptible difference between the Tsushima and the mainland populations of these species. Both of them are primarily lowland inhabitants, have rather a high tolerance for the change of environmental factors, and can easily cross small barriers. Hynobius tsuensis is the unique salamander endemic to the Islands of Tsushima. Its affinity and derivation were discussed by OYAMA (1930), SATO (1943) and others, though no definite opinion has been established. Morphologically, it is somewhat closer to H. nebulosus of West Japan than to H. leechii of Korea and Manchuria. As all the Japanese salamanders of the nebulosus group seem to have been derived from the mother stock of the Asiatic Mainland, the Tsushima population can be regarded as a relict that was left in that area during the southeastward dispersal of the ancestral forms of the species-group. The remaining five species are common between the Tsushimas and Korea, but do not occur in the Japanese main islands. Most of them become differentiated into geographical races, and though two of the five are much more widely distributed and seemingly older in derivation than the others, all can be regarded as "old" species which are less dominant than newly developed ones. They had probably reached Tsushima at an earlier period, ever since settled there, and in certain cases differentiated into endemic subspecies. Their southward dispersal has been barred by the Tsushima Straits, which have, on the other hand, not constituted an effective barrier against the dispersal of more dominant species.
国立科学博物館の論文
1970-10-20

<国立科博専報>対馬の爬虫両生類相小記

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