Context-dependent altitudinal differences in metabolic plasticity of the Asiatic toad

Metabolic plasticity is an essential physiological trait for animal resilience to climate change. Terrestrial ectotherms from thermally stable environments theoretically have a greater capacity for metabolic acclimation than animals from variable environments; however, this has never been tested along an altitudinal gradient. Furthermore, how metabolic plasticity between altitudinal populations may change in the presence of temporal thermal variability remains largely unknown. In this study, we examine the effects of altitude and pre-acclimation thermal variability on the acclimation capacity of resting metabolic rate (RMR) and maximum metabolic rate (MMR) in Asiatic toads (<i>Bufo gargarizans</i>). Our results show that the acclimation capacity of RMR and MMR differs in response to temporal and spatial thermal variability. In terms of RMR, the high- altitude population has lower plasticity than the low altitude population does. Furthermore, this difference increases when the toads experience pre-acclimation thermal variability. In contrast, there is no difference in MMR plasticity between altitude populations or between groups with or without exposure to pre-acclimation thermal variability . However, the thermal sensitivity of the MMR is significantly increased after warm acclimation. In addition, the type of metabolic substrate used depends on the thermal experience prior to thermal acclimation. Overall, our study shows that the plasticity of the metabolic floor but not the metabolic ceiling diverges along altitudinal gradients and is modulated by the thermal context prior to thermal acclimation. Our findings provide new insights into the macrophysiology associated with global warming.