Behavioral thermal variation across phylogenetic and environmental gradients in neotropical ectothermic terrestrial tetrapods

Behavioral thermoregulation is a primary way in which ectotherms avoid overheating, but whether these behavioral limits adjust to climate across broad spatial scales remains poorly understood. Here, we measured the voluntary thermal maximum (VTMax), the temperature at which animals retreat from heat, across 130 species of Neotropical amphibians and reptiles. Comparative analyses were conducted using the subset of 126 species for which complete climatic, geographic, morphological, and phylogenetic information was available. We combined VTMax measurements with species distributions, ERA5 climate records from 1940 to 2024, and time-calibrated phylogenies to test whether behavioral thermal responses are shaped by geography, climate, or evolutionary history. Despite strong climatic contrasts among Neotropical ecoregions, VTMax did not differ significantly among them. Broad-scale climatic and macroecological predictors explained little variation in VTMax after accounting for lineage-level random effects. Amphibians, but not reptiles, showed a modest positive association between VTMax and geographic range size. Overall, VTMax exhibited weak associations with broad-scale climatic and macroecological gradients, while mixed models indicated that part of its variation remained associated with lineage-level structure. These findings suggest that behavioral upper thermal limits respond weakly to broad climatic gradients, supporting the hypothesis that behavioral thermoregulation and local thermal buffering may reduce the coupling between behavioral thermal thresholds and atmospheric conditions.