Thermal biology research compares field with laboratory data to elucidate the evolution of temperature-sensitive traits in ectotherms. The hidden challenge of many of these studies is discerning whether animals actively thermoregulate, since motivation is not typically assessed. By studying the behaviours involved in thermoregulation, we can better understand the mechanisms underlying body temperature control. Using an integrative approach, we assessed the thermoregulatory and thermotactic behaviours of two sympatric snake species with contrasting life histories: the generalist Eastern Garter Snake (Thamnophis sirtalis sirtalis ( Linnaeus, 1758 )) and the semi-fossorial Northern Red-bellied Snake (Storeria occipitomaculata occipitomaculata ( Storer, 1839 )). We expected that thermoregulatory behaviours would be optimized based on life history, in that T. s. sirtalis would show higher evidence for thermally oriented behaviours than S. o. occipitomaculata due to its active nature. Thamnophis sirtalis sirtalis actively thermoregulated, had higher thermal preferences (29.4 ± 2.5 vs. 25.3 ± 3.6 °C), and was more active than S. o. occipitomaculata, which showed relatively low evidence for thermotaxis. Our results build on the notion that evaluating movement patterns and rostral orientation towards a heat source can help ascertain whether animals make thermally motivated choices. Our data provide insight into the thermoregulatory strategies used by snakes with different life histories and maximize the information provided by behavioural thermoregulation experiments.

No abstract

Interspecific variation in metabolic rates may be associated with climate, habitat structure, and resource availability. Despite a strong link between ecology and physiology, there is a dearth in the understanding of how the costs of body maintenance change during ecological transitions. We focused on an ecologically diverse group of neotropical lizards (Tropidurinae) to investigate whether and how resting metabolic rate (RMR) evolved under divergent micro‐ and macrohabitat conditions. Using a phylogenetic framework, we tested whether species from hot and dry habitats had lower RMRs in relation to those from cooler and mesic habitats, and investigated whether microhabitat usage had an effect over body mass‐adjusted RMRs. Our results suggest that RMRs are not phylogenetically structured in Tropidurinae. We found no correlation between metabolism, precipitation, and microhabitat usage. Species from warmer habitats had lower RMR compared to those from cooler habitats, supporting a mechanism of negative compensation in metabolic responses to temperature. Ectotherms from warmer habitats can limit energetic demand and expenditure through reduced RMR, whereas those from cooler habitats may sustain activity despite thermal constraints via increased RMR. Our work highlights the role of temperature in shaping metabolic responses in lizards, giving additional support to the notion that physiology and ecological contexts are intertwined.

No abstract