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 (Bufo gargarizans). 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.

代谢可塑性（Metabolic Plasticity）是动物应对气候变化的关键生理性状。理论上，栖息于热环境稳定区域的陆生外温动物，其代谢驯化（Metabolic Acclimation）能力优于来自热环境波动区域的类群，但该假说从未沿海拔梯度得到验证。此外，当存在短期热波动时，不同海拔种群间的代谢可塑性会发生何种变化，目前仍知之甚少。本研究以中华蟾蜍（Bufo gargarizans）为研究对象，探讨了海拔与驯化前热波动对其静息代谢率（Resting Metabolic Rate, RMR）和最大代谢率（Maximum Metabolic Rate, MMR）驯化能力的影响。研究结果显示，RMR与MMR的驯化能力对短期及空间热波动的响应模式存在差异。就RMR而言，高海拔种群的可塑性低于低海拔种群；且当蟾蜍接受驯化前热波动处理后，这一差异会进一步放大。与之相反，不同海拔种群间，以及是否经历驯化前热波动处理的组别间，MMR的可塑性均无显著差异。但经热驯化后，MMR的热敏感性会显著升高。此外，实验所使用的代谢底物类型，取决于热驯化前的热暴露经历。综上，本研究表明，代谢基础水平的可塑性而非代谢上限的可塑性，会随海拔梯度发生分化，且该可塑性受热驯化前的热环境所调控。本研究结果为与全球变暖相关的宏生理学研究提供了全新视角。