Variation and Systematics of the Malayan Snail-eating Turtle, Malayemys subtrijuga (Schlegel and Müller, 1844)

Allometry, sexual dimorphism, and geographic variation were studied in the Malayan snail-eating turtle, Malayemys subtrijuga (Schlegel and Müller, 1844), using regression and discriminant function analyses. Allometry was evident in M. subtrijuga from the Chao Phraya River Basin. Shell shape changed in males as carapace length increased more than shell width and height, whereas females showed proportional changes. This difference in allometric growth yielded sexually dimorphic adults. Females attained larger sizes and had relatively wider and higher shells than males. Discriminant function analysis of shell and head-stripe characters revealed a clear pattern of geographic variation that was consistent with the topography of Southeast Asia and the poor dispersal abilities of these turtles. Two morphologically distinct groups of Malayemys occur allopatrically in lowland areas of mainland Southeast Asia, and each requires recognition as a distinct species. Turtles from the Mekong River Basin retain the name Malayemys subtrijuga (Schlegel and Müller, 1844), whereas those from the Chao Phraya and Mae Khlong basins, coastal areas of southeastern Thailand, and the Malay Peninsula are assigned the name Malayemys macrocephala (Gray, 1859). Both species are potentially threatened by overcollection and habitat destruction, and should be protected separately. Finally, discriminant function analysis of shell and head-stripe characters suggested that M. subtrijuga on Java were derived from the Mekong River Basin.