Abstract
The Italian wall lizard (Podarcis siculus) living on islets exhibits a melanic skin coloration and a suite of adaptive traits lacking in nearby mainland populations. On islets, the unpredictable environmental conditions and highly fluctuating population densities are believed to have produced reversed island syndrome (RIS). Several physiological, behavioral, and life-history changes based on the RIS could result from positive selection on increased activity of melanocortins. We hypothesize that phenotypes on islets are the product of a plastic variation depending on the regulation of specific genes. Focusing on control systems that determine the insular-adapted phenotype, we demonstrated that reproductive markers, involved in the hypothalamus-hypophysis-gonadal axis, and metabolism markers, flags for hypophysis-melanocortin receptors, are all up-regulated in island lizards under the RIS. This behavior, combined with the observed limited variation in the mitochondrial genome, agrees with the hypothesis that plasticity enables populations to persist in novel environmental conditions and that over time, natural selection will "fine-tune" the population to the environment by modifying the phenotype under selection. We believe that analysis of the transcriptome and the single gene expression, such that all the variations observed in the island populations, can be useful to shed light on evolutionary plasticity as a process affecting animals' populations in general.