Critical Thermal Tolerances and Heating and Cooling Rates of Lizards from Diverse Habitats

Critical Thermal Maxima and Minima (CTMax and CTMin) were determined for four lizard species which represent a wide range of environmental and behavioral diversity, thereby defining the range of thermal tolerance for each species. Specimens of Anolis carolinensis, Sceloporus occidentalis, and Phrynosoma cornutum, all members of the family Iguanidae, exhibited panting responses during heating. This response was absent in Xantusia vigilis. Living animals heated and cooled more rapidly and more erratically than did dead individuals in all four species. The CTMax of P. cornutum (46.8-48.1? C) was significantly higher than that of the other species at all acclimation temperatures. In X. vigilis acclimated to 15? and 25? C the CTMax (40.1 and 40.7? C, respectively) were lower than those of the other species held at the same acclimation temperatures. The lowest CTMin recorded was that of X. vigilis acclimated at 25? C (4.3? C); the highest was that of A. carolinensis acclimated at 35? C (16.5? C). Acclimation temperature significantly affected the CTMin of all species at some experimental conditions and had a significant effect upon the CTMax of A. carolinensis and X. vigilis. P. cornutum had a range of thermal tolerance of approximately 40? C; other species had thermal tolerance ranges of about 30? C. These ranges are correlated with the distribution and ecology of the species studied.