Introduced alien or persecuted native? Resolving the origin of the viperine snake (Natrix maura) on Mallorca

The viperine snake (Natrix maura) is an important agent of decline of the threatened midwife toad (Alytes muletensis) of Mallorca. However, there is a paucity of biological data to support the notion that the viperine snake is an introduced species to the island. Here we compare mitochondrial cytochrome b gene sequences and genomic ISSR-PCR fingerprints from Mallorcan and mainland European viperine snakes. Identical or nearly identical haplotypes and very similar ISSR-PCR profiles provide strong evidence that N. maura arrived only recently to Mallorca. There is no indication of a recent natural colonization of the island by transmarine dispersal. The data therefore support historical information that N. maura was introduced to Mallorca by human agency comparatively recently, and that management measures to reduce the impact of the snake on toad populations are justified.