Behavioural attitudes and regulation of temperature in Amphibolurus lizards



The contribution of discrete behavioural attitudes towards temperature regulation has been studied, both in the field and in the laboratory, in five species of Agamid lizards of the genus Amphibolurus. This genus has radiated widely in the arid and semi-arid areas of Australia and the species selected for study were chosen to represent, as closely as possible, the range of habitats occupied by the genus. Behaviour patterns thought to be of significance in temperature regulation have been characterized thermally in terms of the mean body temperature and the set of mean environmental temperatures at which they have been observed. When comparisons are made between the temperature specificities of similar and analogous behaviour patterns displayed by species from different habitats, few significant differences emerge. Thus, desert-living species show no greater tolerance towards grossly elevated body temperatures than do species from less severe habitats, when similarly temperature acclimated, although the former are exposed daily to environmental temperatures much greater than those prevailing in semi-arid and sub-humid habitats. Selection for the ability to tolerate increased body temperatures therefore does not appear to have operated in the genus, due to the efficacy of the thermoregulatory behaviour of these lizards. All species, however, depend upon the presence of thermal refuges for their survival during the hottest periods of the day, and this is especially so for species inhabiting very hot dry habitats. Desert-inhabiting species are also obliged to spend considerable periods of the day in high-temperature avoidance behaviour patterns and are thus forced to endure long daily exposures to body temperatures above those preferred for activity. Short-term acclimatory adjustments in temperature tolerance assist the animals in surviving this exposure. The situation with Amphibolurus contrasts strongly with that found in other desert-living agamids, such as Diporophora, which are unable to avoid effectively the heat of the day and show an ability to tolerate high body temperatures far in excess of the most thermophilic Amphibolurus species.