A study in scarlet: incipient speciation, phenotypic differentiation and conservation implications of the Podarcis lizards of the western Pontine Islands, Italy

During the first decades of the last century, an enigmatic extinction was documented to have occurred on the small Mediterranean island of Santo Stefano in the Pontine Archipelago. Although islands are fascinating systems for studying microevolutionary processes, they may nevertheless host unstable communities that make their populations particularly vulnerable to anthropogenic effects and, ultimately, extinction. Here, we investigated the variation of head morphology of 374 individuals of Podarcis siculus from mainland Italy, Sicily and the Pontine Archipelago, using geometric morphometrics. We also included in the analysis samples of the extinct population of Santo Stefano Island, aiming to shed light on the extinction and provide additional information on the historical biogeography of the Archipelago. We found a strong relationship between morphological differences and phylogeographical structure based on previously published genetic data, indicating that the western Pontine populations seem to be a case of incipient speciation. In addition, the extinct population of Santo Stefano Island clustered in all analyses with the western Pontine populations. The results not only provide information on the evolutionary history of P. siculus, but also lead to broader considerations of taxonomy and conservation.