Geographic variation in the endemic skink, Ateuchosaurus pellopleurus fromthe Ryukyu Archipelago, Japan

Variation in 28 quantitative characters and one qualitative character in th e endemic Ryukyu skink Ateuchosaurus pellopleurus was analyzed. Multivariat e analysis of the quantitative characters revealed extensive variation amon g the insular populations. Branching topology in the neighbor-joining pheno gram deriving from Mahalanobis distances among island samples coincides wel l with their geographic arrangement, suggesting a great contribution of geo history to the branching pattern. By contrast, branch length in the phenogr am does not seem to reflect the paleogeography well, presumably due to nois e from rapid morphological changes in small island populations. None of our analyses demonstrated distinct divergence between populations on islands n ortheast and southwest of the Tokara Tectonic Strait. Accepting the current paleogeographical hypothesis that this strait has consistently existed sin ce its initial formation in the Pliocene, we interpret this result as indic ative of recent oversea dispersal across the strait. Results of the analyse s also suggested that in A. pellopleurus primary divergence occurred betwee n populations of the Okinawa Group and the remainder. Nevertheless, because of the absence of even a single discriminant character between these two g roups, we reject taxonomic subdivision of the species proposed by a few pre vious authors.