Micro-scale differences in thermal habitat quality and a possible case of evolutionary flexibility in the thermal physiology of lacertid lizards.

We studied the thermal ecology of the lacertid lizards Lacerta oxycephala and Podarcis melisellensis on the Adriatic island of Vis (Croatia) during summer. These species obviously differ in microhabitat use: L. oxycephala climbs on rocks and stone walls, whereas P. melisellensis is mainly ground-dwelling in vegetation. Since theoretical considerations predict a difference in thermal quality between the species' microhabitats, this system seems to present a good opportunity to test the influence of thermal microhabitat quality on body temperature, thermoregulatory behaviour and evolution of thermal characteristics. Data on thermoregulatory behaviour, body temperatures (T ) and habitat quality were collected in the field and selected temperatures (T ) were estimated in a laboratory thermogradient. Accuracy and effectiveness of thermoregulation were quantified. Thermoregulatory behaviour consisted of timing of activity, selection of places in full sun and near sun-shade transitions, and basking. As predicted, L. oxycephala occupied the microhabitat with the lower thermal quality and had on average a lower T . However, L. oxycephala also selected lower temperatures in the experimental thermogradient. Thus, if T can be regarded as the thermoregulatory target, both species proved to be accurate and effective thermoregulators. These results corroborate the "labile view" on the evolution of thermal physiology: both L. oxcephala and P. melisellensis appear to be adapted to their respective thermal microhabitat. This is a surprising conclusion, since earlier studies have found the thermal characteristics of Lacertidae to be evolutionarily rigid.