Alborán island, a small meeting point for three invasive lizards, whose geographic origin is uncovered by molecular analysis

Abstract

Alborán is a small volcanic island located in the center of the Alborán Sea, W Mediterranean, 85 km from the Iberian Peninsula (Europe) and 55.5 km from the NW African coast line. Despite its small size (605 × 265 m), four distinct exotic lizard species have already been reported there, one of them presumably extinct (Saurodactylus mauritanicus). Throughout history, the island has maintained an intermittent human presence, being now permanently occupied by a military detachment connected to the Iberian Peninsula mainly by means of cargo shipments. Hence, this communication between the island and the continent has fuelled human-mediated species introductions. Populations of the geckos Tarentola mauritanica and Hemidactylus turcicus and the most recently reported wall lizard Podarcis vaucheri still remain in the island. Here, we used molecular tools to assess species identity and putative invasion pathways. As expected, results confirm the initial species assignement and indicate southern Iberia as the source area. However, surprisingly, two clades of T. mauritanica were found, the European clade commonly introduced elsewhere, and the Iberian clade, reported here for the first time outside its native distribution. Moreover, the reported southern Iberian lineage of P. vaucheri in Alborán, represents the third case of introduction of this species. This amazing concentration of alien species in such a reduced territory highlights how prone small islands are to be sucessfully invaded, and that these should not be neglected in invasion biology. The effects of these alien reptile species over native taxa are yet unknown, although an impact over several endemic invertebrates cannot be ruled out. As such, regular monitoring should be implemented to prevent they act as hubs for future new introductions.