The functional significance of panting as a mechanism of thermoregulation and its relationship to the critical thermal maxima in lizards.

Because most desert-dwelling lizards rely primarily on behavioral thermoregulation for the maintenance of active body temperature, the effectiveness of panting as a thermoregulatory mechanism for evaporative cooling has not been widely explored. We measured changes in body temperature (T b) with increasing air temperature (T a) for 17 species of lizards that range across New Mexico and Arizona and quantified the temperatures associated with the onset of panting, and the capacity of individuals to depress T b below T a while panting, and estimated the critical thermal maxima (CTmax) for each individual. We examined these variables as a function of phylogeny, body mass and local acclimatization temperature. We found that many species can depress T b 2-3°C below T a while panting, and the capacity to do so appears to be a function of each species' ecology and thermal environment, rather than phylogeny. Panting thresholds and CTmax values are phylogenetically conserved within groups. Understanding the functional significance of panting and its potential importance as a thermoregulatory mechanism will improve our understanding of the potential for species' persistence in an increasingly warmer world.