Predicted sea-level changes and evolutionary estimates for age of isolation in Central Mediterranean insular lizards

Rates of biological evolution on islands are often presumed to exceed rates on the mainland. We tested this postulation by computing the evolutionary rate of head shape in Italian wall lizard Podarcis siculus, occurring on four islands off the coast of Southern Italy. We calculated the evolutionary rate using a phylogenetic tree whose node ages were derived from Lambeck et al. predicted ages of geographic isolation of the islands. Such ages are based on a relative sea-level change model for the late Pleistocene–Holocene. Through a likelihood optimization procedure, our method allows computing, besides the evolutionary rate, biological estimates of the ages of insular populations, with this indirectly testing Lambeck et al.’s model estimates. We found that the rate of evolution in Podarcis head shapes on islands is not statistically different from the mainland rate, although insular lizards have distinctive head shapes. Overall, the insular phenotype took 1–4000 years to arise (differing among islands). The estimated ages of insular populations are lower than Lambeck et al.’s estimates and fall in the 5- to 6-ka interval.