The role of island physiography in maintaining genetic diversity in the endemic Tyrrhenian wall lizard (Podarcis tiliguerta)

Sea level oscillations occurred during the Pleistocene have strongly affected islands’ physiography by changing area, elevation, and even the number of islands rising above the sea level. Such changes had direct consequences on island genetic diversity by promoting genetic admixture during glacial marine regressions while fragmentation or even extinctions occurred because of marine transgressions. Here we investigated the effect of islands’ physiographic changes on the mitochondrial diversity of 84 individuals of the Tyrrhenian wall lizard (Podarcis tiliguerta) from different islands and island groups surrounding Corsica and Sardinia. The La Maddalena Archipelago that is the more complex of the studied island groups, showed the highest genetic diversity, while we detected decreasing genetic diversity in island groups with lower number of islands and elevation. The genetic imprint we found seems to have been shaped by eustatic changes occurred in the Mediterranean basin during Mid-Pleistocene times. Indeed, a relevant component of ancient lineages was found on those island groups among which elevation of at least one island allowed populations to survive during the Mid-Pleistocene marine transgressions. In contrast, we found evidence of recent gene flow between populations inhabiting islands or island groups characterized by low elevation. Our results suggest that many features such as number of islands and their elevation, may provide predictive information to identify those islands or “archipelagos” that deserve special attention in terms of conservation priority.