Thermal Variability Modulates Altitudinal Differences in Metabolic Plasticity of the Asiatic Toad

Physiological plasticity is crucial for survival in fluctuating environments. The climate variability hypothesis (CVH) proposes that physiological plasticity scales with climatic variation across geographical gradients, yet its generality remains debated. Furthermore, the mediating role of prior thermal history is largely unexplored. This study examines how altitude and thermal variation shape phenotypic plasticity in resting metabolic rate (RMR) and maximum metabolic rate (MMR) of Asiatic toads (Bufo gargarizans). We found that RMR plasticity, but not MMR plasticity, varied altitudinally and was influenced by thermal conditions. Compared to low-altitude toads, high-altitude individuals exhibited reduced RMR plasticity, contradicting the CVH. This difference was amplified under higher thermal variability. In contrast, MMR plasticity showed no altitudinal variation or response to thermal variability. However, warm acclimation significantly increased MMR thermal sensitivity. Metabolic substrate choice depended on pre-acclimation thermal experience. Our results indicate that RMR plasticity, rather than MMR plasticity, primarily underpins altitudinal adaptation, and increased thermal fluctuation may disrupt this adaptive pattern. This research provides novel insights into macrophysiological responses to global warming.