Surviving on a Rock, but for How Long? Deviations in the Thermoregulatory Strategy of the Milos Wall Lizard (Podarcis milensis)

Abstract

Reptiles are unable to generate metabolic heat and regulate body temperature behaviorally depending on environmental conditions. The thermal quality of their habitat is therefore of pivotal importance for their survival. Lizards render themselves as ideal ectothermic models, and their thermal biology has been extensively studied. In this work, we focused on the thermoregulatory performance of the endemic Milos wall lizard (Podarcis milensis) (Milos Archipelago, Aegean Sea, Greece). Applying the same standard methodology, we estimated the effectiveness of thermoregulation (E) taking into account the three main thermal parameters: body (Tb, the temperature of active animals in the field), environmental (Te, the temperature that animals would achieve in the field if passively conform to the environment) and preferred temperatures (Tpref, the temperatures an animal achieves in a laboratory thermal gradient). Here, we compare the thermoregulatory profile of two remote rocky islet populations, Falconera and Velopoula, with the Milos Island population. We collected Tb values from active lizards as well as Te from specially designed copper models, which were appropriately placed in the field so as to cover all possible microhabitats. Lizards were then transported to the laboratory where we assessed their Tprefs. Falconera and Velopoula populations showed the same high thermoregulatory effectiveness as that of Milos Island (EFalconera = 0.97, EVelopoula = 0.95, EMilos = 0.89). However, when we used an alternative evaluation of the thermoregulatory strategy, the E values outlined a much more effective thermoregulation for the islets: de-dbFalconera = 6.97, de-dbVelopoula = 11.54, de-dbMilos = 4.27. The adverse conditions on the islets outline a demanding habitat of low thermal quality that dictates effective thermoregulation. However, the trend of increasing temperatures depicts an even harsher environment for the years to come. Could lizards that have already achieved the highest thermoregulatory effectiveness and cannot escape from the isolated islets they dwell cope with these new conditions? This is the kind of questions to which conservation biology will be called upon to respond.