Inttra-and interspecific genetic exchanges in Japanese small mammals through the Quaternary environmental fluctuations

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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. The fauna is also complex because Japan is long in a south to north direction and potentially has many geographic borders. To understand the organization of Japanese small rodents, we examined intra- and interspecific genetic variation in Japanese small mammals, such as dormice, murine and voles, from three geographic domains of Hokkaido, Honshu-Shikoku-Kyushu and Ryukyu Islands, using nucleotide sequences for the mitochondrial cytochrome b and nuclear IRBP genes and compared them with those of species collected from the Asian continent, Genetic divergence indicated that Japanese small rodents possess relatively high species endemism, especially in the Honshu and Ryukyu domains. Levels of genetic variation differ among species from the same geographic domains : however, suggesting a complex evolutionary history that is species-specific. High levels of genetic diversity were observed among geographic populations of Glirulus japonicus, Eothenomys andersoni, Apodemus speciosus. and Tokudaia osimensis as well as between Japanese and continental populations of Clethrionomys rufocanus and C.rutilus. These data imply that the Japanese islands had played and important roll in increasing the levels of genetic and species diversity in East Asia. Moreover, considering the molecular phylogenies and distribution patterns, it is probable that frequent interspecific and interpopulational genetic exchanges have taken place during the course of speciation in many small mammalian species.