Evolutionary and environmental determinants of heat tolerance and acclimation capacity in herpetofauna

Exploring heat tolerance and acclimation capacity can provide an effective approach to evaluating species' sensitivity to extremely high temperatures due to climate warming. Despite some work on amphibian and reptile thermophysiological adaptation, related questions remain. We reviewed the literature to provide a synthesis of worldwide data on heat tolerance and to determine the relative importance of common evolutionary and environmental thermal variation in amphibians and reptiles in shaping species' heat tolerance and acclimation capacity. The phylogenetic conservatism in amphibian and reptile heat tolerance arose from distinct phylogenetic properties and thermal habitat variables, potentially attributable to their different environmental sensitivities and contrasting life-history characteristics. The heat tolerances of amphibians and reptiles showed significant correlations with thermal habitat variations, which is consistent with the climate variability hypothesis that species inhabiting thermally fluctuating environments develop broader environmental tolerance ranges. No significant association was detected between species' thermal habitat variation and acclimation capacity in these 2 taxa. This finding confirmed that the interaction between maintenance cost (i.e., overall external environments) and production cost (i.e., specific environmental variables) underlaid the evolution of thermal acclimation capacity. Our results showed the importance of adaptive evolution and phylogenetic conservation in molding thermophysiological traits in amphibians and reptiles. Future studies should focus on intraspecific associations between thermophysiological traits and phylogenetic factors in species across various environmental gradients.