Genetic interaction between Russian and Japanese small mammals.

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The fauna of Japanese small mammals is thought to be complex because frequent migration events might have occurred during the last several million years from three different routes through Sakhalin, the Korean Peninsula, and Taiwan. Here we examined the Sakhalin route to elucidate the evolutionary history of the fauna of small mammals of Hokkaido, using molecular phylogenetic tools including mitochondrial and nuclear DNAs. We observed considerable extent of difference in the levels of genetic endemism and geographic variation among the species examined. Hokkaido's small rodents possessed relatively low species endemism. The levels were relatively, high in Clethrionomys rex and low in Apodemus peninsulae. The levels of geographic variation were high in Clethrionomys rufocanus and C. rutilus and low in A. peninsulae and C. rex. Our data imply that Hokkaido had played an important role in increasing the levels of the biodiversity in East Asia during the past one or two million years. The patterns of speciation and geographic variation of small mammals in East Asia were considered to be affected by the Quaternary environmental changes, such as expansion of permafrost and emergence of land bridges