Complex Historical Biogeography of the Eastern Japanese Skink, (Scincidae, Squamata), Revealed by Geographic Variation in Molecular and Morphological Characters.

We investigated the geographic diversification of , which occurs in the central to northern parts of the Japanese Islands, based on a time-calibrated mitochondrial DNA (mtDNA) phylogeny and external morphological characters. The mtDNA phylogeny suggests that diverged from its sister species in western Japan 2.82-4.63 million years ago (MYA), which can be explained by geographic isolation due to the spread of sedimentary basins in the Pliocene. The primary intraspecific divergence was that between lineages in central and northeastern Japan 1.58-2.76 MYA, which could have been caused by the upliftings of major mountain ranges. In the northeastern lineage, mtDNA and morphological characters suggest a geographic differentiation between sub-lineages of the northwestern Tohoku District (α) and other areas (β). Although the sub-lineage β occurs in a disjunct geographic range, consisting of Hokkaido and the central to south of Tohoku, these areas are bridged by populations with intermediate characteristics along the Pacific side of northern Tohoku. Overall, the geographic variation in in northern Japan can be explained by an initial allopatric divergence of the sub-lineages α and β at 0.71-1.39 MYA, a recent northward expansion of the sub-lineage β, and subsequent secondary introgressive hybridization between the sub-lineages.