Genetic Structure of the Asiatic Black Bear in Japan Using Mitochondrial DNA Analysis

The genetic structure of the Asiatic black bear (Ursus thibetanus) in Japan was studied to understand the events that occurred during its evolution. The left domain of the mitochondrial control region (about 240 bp) was sequenced, defining 27 haplotypes that consisted of 23 haplotypes from 333 bears in Japan and 22 bears in the Asian continent. The network tree of the control region indicated that the Japanese population formed a distinct clade from the continental population. The phylogeographic analysis of the haplotypes indicated that the Shikoku and Kii Hanto populations had diverged during the initial phase from the ancestral population. After the 3 dominant haplotypes were rapidly distributed throughout Japan in the early stage of the population dispersal, the Japanese population diverged into eastern and western populations. Using the entire mitochondrial cytochrome b sequence, divergence time between the Japanese and the Continental populations suggested that the Japanese population might have colonized into Japan through the land bridge from the Korean Peninsula around 500 ka, which is consistent with paleontological evidence. Our finding that bears in western Japan exhibit lower genetic diversity and higher levels of genetic differentiation than bears in eastern Japan provides a vital contribution to conservation policy for these isolated populations.