Small Island Effects on the Thermal Biology of the Endemic Mediterranean Lizard Podarcis gaigeae

SIMPLE SUMMARY: As ectotherms that do not produce metabolic heat to regulate their body temperature, lizards largely rely on the thermal quality of the environment for most aspects of their biology. To compensate for geographically induced changes in the thermal environment, different lizard populations within a single species should either regulate their behavior or shift their thermal preferences, responding to directional selection. Here, we studied the thermal ecology of the endemic Skyros wall lizard (Podarcis gaigeae) and assessed the influence of thermal habitat quality on body temperature and preferred body temperatures. Our findings suggest that the species thermoregulate effectively in a wide variety of habitats and support the view that the thermal characteristics of certain species are plastic and respond to environmental changes. ABSTRACT: Ectotherms are vastly affected by climatic conditions as they rely on external sources of heat to regulate their body temperature, and changes in their habitat thermal quality could seriously affect their overall biology. To overcome the problems of a thermally unfavorable habitat, lizards need to either adjust their thermoregulatory behavior or respond to directional selection and shift their preferred body temperatures. To assess the impact of habitat thermal quality on the thermoregulatory profile, we studied multiple islet and ‘mainland’ populations of the Skyros wall lizard Podarcis gaigeae, an endemic lacertid to Skyros Archipelago, Greece. We evaluated the effectiveness of thermoregulation (E) using the three main thermal parameters: body (T(b)), operative (T(e)), and preferred (T(pref)) temperatures. We first hypothesized that the spatial homogeneity, the scarcity of thermal shelters, and the exposure to higher winds on islets would result in more demanding climate conditions. Second, we anticipated that islet lizards would achieve higher E in response to the lower thermal quality therein. As hypothesized, thermal parameters differed between populations but not in the expected manner. Skyros ‘mainland’ habitats reached higher temperatures, had more intense fluctuations, and were of lower thermal quality. As a result, lizards showed higher accuracy, precision, and effectiveness of thermoregulation. Noteworthy, we found that lizards from different populations have shifted their thermal profile and preferred body temperatures to cope with the particular conditions prevailing in their habitats. The latter supports the labile view on the evolution of thermoregulation.