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 and Sherlock Holmes was jokingly evoked to solve the mystery. Although islands are fascinating systems where to study microevolutionary processes, they may, on the other hand, host unstable communities that make their populations particularly vulnerable to anthropogenic effects and even to extinctions. Here, we investigated the variation of head morphology of 374 individuals of Podarcis siculus from mainland Italy, Sicily and the Pontine Archipelago, using the geometric morphometric approach. We also included in the analysis samples of the extinct population of Santo Stefano Island aiming to contribute to shed light on the “mystery” and to provide additional information on the historical biogeography of the Archipelago. We found strong relation between the morphological differences and the phylogeographic structure basing 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. This result not only involves the evolutionary history of P. siculus, but also entails broader taxonomic considerations and conservation aspects .