The influence of climatic oscillations during the Quaternary Era on the genetic structure of Asian black bears in Japan.

The Asian black bear (Ursus thibetanus) inhabits two of the main islands, Honshu and Shikoku, in Japan. To determine how climatic oscillations during the Quaternary Era affected the genetic structure of the black bear populations in Japan, we examined their phylogeographic relationships and compared their genetic structure. We analysed an approximately 700-bp sequence in the D-loop region of mitochondrial DNA collected from 589 bears in this study with 108 bears from a previous study. We observed a total of 57 haplotypes and categorized them into three clusters (Eastern, Western and Southern) based on the spatial distribution of the haplotypes. All but 2 of the 41 haplotypes in the Eastern cluster were distributed locally. Genetic diversity was generally low in northern Japan and high in central Japan. Demographic tests rejected the expansion model in northern populations. Haplotypes of the Western and Southern clusters were unique to local populations. We conclude that the extant genetic structure of the Asian black bear populations arose as follows: first, populations became small and genetic drift decreased genetic diversity in the northern area during the last glacial period, whereas large continuous populations existed in the southern part of central Japan. These patterns were essentially maintained until the present time. In western and southern Japan, the effects of climatic oscillations were smaller, and thus, local structure was maintained.