Does hybridisation with an invasive species threaten Europe’s most endangered reptile? Genomic assessment of Aeolian lizards on Vulcano island

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. However, pure P. raffonei showed extremely low genetic diversity, a very small effective population size, and a low N E /N C ratio. Management strategies are urgently needed to control invasive species and maintain the genetic diversity of P. raffonei .