The impact of Pleistocene glaciations on population structure and systematics in five snake species in the Banda Arc islands of southern Wallacea: the views from genes, morphology and species assemblages

Wallacea is a region of geographic overlap in biotas derived from both Asian and Australasian continental plates. Species have also evolved rapidly over the last few (ca. 5) million years, aided by isolation and dynamic changes in island extents during the Pleistocene, to produce high levels of endemism. Vertebrate surveys on 26 islands some 30 years ago confirmed the high diversity of reptiles in the Inner and Outer Banda Arcs of Wallacea and numerous species endemic to the region. Here we assess the genetic relationships of island populations of five snake taxa (Dendrelaphis inornatus, Coelognathus subradiatus, Lycodon capucinus, Psammodynastes pulverulentus, Trimeresurus insularis) that we had previously examined using only morphological variables. Island heterozygosity is within the range generally reported for reptiles, although on the low side, consistent with their island location. One of the five species we examined, Trimeresurus insularis, shows a statistically significant decline in island mean heterozygosity from west to east, a phenomenon we have observed in some mammalian species in the Banda Arcs. Genetic data confirm speciation and endemism in the Banda Arcs within the genus Dendrelaphis. Populations on Kai and Yamdena islands on the Outer Banda Arc are genetically distinct from those on the islands to their west and are closely allied to the recently described D. grismeri from the Maluku islands. Dendrelaphis pictus occurs on Lombok and Nusa Penida, whereas D. inornatus spans the intervening islands of the Lesser Sunda Islands. Within all taxa, aggregations of island populations that are genetically alike are almost always geographically separated from genetically different groups by straits that persisted through the last Pleistocene glaciation. However, genetic differentiation is not invariably associated with these Pleistocene-persistent straits. Several snake species on Alor, on the Inner Banda Arc, are more closely allied to those on Timor and other Outer Banda Arc islands, and some on Sumba, within the Outer Banda Arc, are genetically closest to populations on the nearby Inner Banda Arc islands. The major separation of snake assemblages across Lesser Sunda Islands coincides with a Pleistocene-persistent sea barrier.