Geographic variation and sexual size dimorphism in Mauremys mutica (Cantor, 1842) (Reptilia: Bataguridae), with description of a new subspecies from the Southern Ryukyus, Japan

Abstract

The batagurid turtle, Mauremys mutica, is widely distributed in tropical to temperate East Asia. Analyses of morphometric characters and coloration revealed that the southern Ryukyu populations of this species are much diverged from the other populations, presumably as a result of their long geographical isolation. We describe those populations as a new subspecies, M. m. kami. Analysis of geographic variation also suggested that distinctly isolated populations of the central and northern Ryukyus, and Kyoto and Shiga Prefectures of central Japan have originated from animals artificially introduced from the Yaeyama Group, and Taiwan, respectively. We confirmed the absence of "larger female" sexual size dimorphism (SSD) in M. mutica unlike most other aquatic batagurids, and further demonstrated variation in SSD pattern between the subspecies: in M. m. kami, the adult male has a significantly greater carapace length than adult females, whereas the adult carapace length does not differ significantly between sexes in the nominotypical subspecies. It is hypothesized that these dimorphic patterns evolved from the widely prevailing "larger female" condition through epigamic selection involving forcible copulatory behavior.