Microhabitat and ontogenetic variation of thermal tolerance in complex ectotherm life cycles

Thermal tolerances, such as critical temperatures, are important indices for understanding an organism's vulnerability to changing environmental temperature. Differences in thermal tolerance over ontogeny may generate a thermal bottleneck that sets the climate vulnerability for organisms with complex life cycles. However, a species' microhabitat preference and life history can hinder our ability to assess climate change vulnerability in large-scale comparative studies as these reflect local adaptation. Here, we used phylogenetically informed, multi-level models with a global dataset of upper critical temperatures from 438 Anuran species that explicitly included microhabitat preferences and ontogenetic stage to examine variation in upper critical temperatures. We found ontogenetic trends in thermal tolerance were similar across microhabitat preferences. We then used microclimate-driven models of the heat and water budget of a thermoregulating frog to show the contribution of behavioural thermoregulation towards mitigating exposure to thermal stress. Our results suggested thermal bottlenecks are not strongly present in Anurans but instead implied strong developmental or genetic conservatism of thermal tolerance within families and ecotypes, and that behavioural thermoregulation has a strong potential for buffering frogs against extreme temperatures.