Abstract
Two invasive lineages of Black Rat (the Rattus rattus species complex) occur in Japan: the newly introduced Rattus rattus (2n=38) of Indian and European origin, and the anciently introduced R. tanezumi (2n=42) of East Asian origin. To assess the current distribution and invasion history of these lineages, we determined the nucleotide sequences of a coat color-related gene, melanocortin 1 receptor (Mc1r, 954 bp), in 36 rats from Japan and conducted phylogenetic analyses for a total of 133 rats mainly from Japan (17 localities). Mc1r haplotypes representing R. rattus were recovered from Otaru, the Ogasawara Islands, and Tokyo, and heterozygous individuals with the R. tanezumi type sequences were detected in these localities. These results imply that introgressive hybridization is currently going on in a variety of places in Japan such as urban and port areas, and on remote islands. In contrast, the R. rattus haplotypes were not detected in the natural forests of the Ryukyu Islands here represented by the islands of Amamioshima and Okinawa, implying the presence of some mechanism preventing the introduction of the invading lineage. We recovered some endemic haplotypes from the Ryukyu Islands, suggesting genetic differentiation between the Ryukyu Islands and other parts of Japan.
