Abstract
The Ryukyu five-lined skink, Eumeces marginatus, is an endemic species of the central and northern Ryukyus, and is composed of two morphologically defined subspecies, E. m. marginatus from the Okinawa Group, and E. m. oshimensis from the Amami and Tokara Groups. A population of the genus Eumeces, recently found on Iotorishima Island (an uninhabited islet located north of the main island chain of the Ryukyus), resembles E. m, oshimensis in having a relatively short median white line on the tail, but is distinct from any population of E. marginatus in having more midbody scale rows. To assess the taxonomic status of the Iotorishima population from a historical viewpoint, we examined its genetic relationships with E. marginatus populations. The degree of genetic differentiation between the Iotorishima population and a population of E. m. oshimensis from Tokunoshima, northern Amami islands, was fairly low (D=0.043). Cluster analysis of genetic data also indicated that the Iotorishima population constitutes one of the two major clusters within E. marginatus together with four E. m. oshimensis populations from the northern Amami and southern Tokara islands. Thus, it is likely that the number of midbody scale rows in the Iotorishima population has increased rapidly after its relatively recent isolation. Taxonomically, the Iotorishima population seems to be most appropriately assigned to E. m. oshimensis.
