First Record of Lineage IV of Rattus tanezumi (Rodentia: Muridae) from the southern Ryukyus, Japan

Based on mitochondrial cytochrome b gene sequences, we report representatives of the Lineage IV of Rattus tanezumi (Rodentia: Muridae) from Miyakojima, Taramajima, and Yonagunijima Islands in the southern Ryukyus as the first record of the lineage from Japan. The new record of Lineage IV provides an addition to the mammal fauna of Japan essentially at the species level. Accordingly, the genus Rattus in Japan consists of five species: R. rattus, Lineage II of R. tanezumi, Lineage IV of R. tanezumi, R. norvegicus, and R. exulans. The Miyakojima–Taramajima and Yonagunijima samples of the Lineage IV had discernible genetic differences, suggesting different origins. From Miyakojima Island and Kojima Island (an islet close to Miyakojima Island). We also found Lineage II of R. tanezumi, indicating that the two lineages coexist on Miyakojima Island. Morphological comparisons of these Lineage IV and Lineage II specimens suggest a greater molar length in Lineage IV than in Lineage II, and differences in the foramen magnum shape. Future detailed studies on genetic structures, morphological characteristics, and distribution of Lineage IV and Lineage II rats in the southern Ryukyus are needed to clarify their evolutionary history.