Thermal acclimation in temperate lizards

Abstract

THERMAL acclimation has been studied most intensively in aquatic ectotherms¹ in which body temperature closely approximates water temperature, which changes slowly with season. As aquatic ectotherms must therefore be active over a range of slowly changing body temperatures, acclimation usually functions as a homeostatic mechanism; following a temperature change in the environment, the organism's metabolic rate is adjusted so that it is returned to near its original level². Some terrestrial animals, particularly reptiles which thermoregulate behaviourally, are subject to considerable daily fluctuations in body temperature³. This difference in the thermal ecology of aquatic ectotherms and terrestrial reptiles, which may cause a difference in the acclimatory responses of the two groups, has not been considered in the work on thermal acclimation in reptiles^4–6. Consequently, this work is of little use in predicting the acclimatory responses of reptiles to seasonal temperature changes in the field. We present here evidence that lizards allowed to thermoregulate behaviourally acclimate only at low body temperatures and that the common pattern of acclimation differs from that of aquatic organisms in being determined by requirements of low temperature energy conservation rather than metabolic homeostasis.