Hybridisation between Podarcis siculus and Podarcis raffonei. Hybridisation between Podarcis siculus and Podarcis raffonei

Interspecific hybridisation can be consequential for rare and insular endemic species. The Critically Endangered Aeolian wall lizard, Podarcis raffonei, severely declined due to interactions with the invasive Italian wall lizard, Podarcis siculus. The largest population of P. raffonei survives on a narrow peninsula (Capo Grosso) that is mildly connected to the island of Vulcano, which has been entirely invaded by P. siculus. Recent observation of individuals with an intermediate phenotype raised concern over the risk that hybridisation might swamp this last stronghold. We genetically characterised lizards from Vulcano using genome-wide SNPs, considering individuals showing multiple phenotypes (native, invasive, and "intermediate"). Hybridisation rate was low (~3%), with just two F1 hybrids and two backcrosses. We cautiously suggest that hybridisation does not currently represent the major threat for P. raffonei in Capo Grosso. However, we identified extremely low genetic diversity, a small effective population size, and a low NE/NC ratio. Management strategies are urgently needed to control invasive species and maintain the genetic diversity of P. raffonei.