Taxonomic Status of the Taiwanese Populations of Rhabdophis tigrinus (Squamata: Colubridae)

Taxonomic treatment of the Taiwanese populations of Rhabdophis tigrinus has been controversial. Some authors adopt a subspecific name, R. t. formosanus, whereas others negate taxonomic subdivision of R. tigrinus. We compared external characters and karyotype between the Taiwanese and other populations. Results indicate that the former has a unique W chromosome, which is metacentric and distinctly smaller than the Z chromosome. The Taiwanese populations also differ from others, except for populations of Kyushu, Japan, in having more subcaudals (80≦in males, 77≦in females). From the Kyushu populations, Taiwanese R. tigrinus is distinct in having 15 or more lateral dark blotches between the neck and the 50th ventral (14≧in the former). All these characters, as well as deduced East Asian paleogeography, strongly suggest that the Taiwanese populations have been constituting an independent evolutionary unit by themselves since their entry into this island from the southeastern continent. Thus, we consider that they deserve recognition as a distinct taxon and tentatively retain them at the subspecific status as R. t. formosanus.