Effects of Climate Warming on Overwintering of Qinghai Toad-Headed Lizards at Two Contrasting Elevations

Increases in temperature associated with global warming have significant implications for organismal fitness. Thermal condition changes of inactive or dormant periods (such as winters) also have important effects on animals, particularly for ectotherms. Neglecting the potential consequences of winter warming can lead to biases in assessing the effect of climate change. The impacts of winter warming on ectotherms may be complex and multifaceted, possibly varying with geographic location including thermal ecological niche, altitude, and latitude. Therefore, we conducted field warming experiments (warmer climate vs. present climate) to investigate the effects of winter warming on the mass loss, body condition, physiological process, and survival capacity of Qinghai toad-headed lizards (Phrynocephalus vlangalii) at two contrasting altitudes (2600 vs. 3600 m) of the northern Qinghai-Xizang Plateau, China. The warming treatment reduced mass loss of the 2600-m-altitude lizard population, enhanced body condition, and increased overwintering survival rate after hibernation, while there was no significant effect on these indicators for the 3600-m-altitude lizard population with warming treatment. The two altitudinal populations showed different regulatory patterns of metabolic pathways in response to warming winters. Under simulated warming, the 2600-m-altitude lizard population mostly downregulated energy metabolism-related pathways (e.g., glycolysis, pyruvate metabolism, fatty acid degradation, TCA cycle, and oxidative phosphorylation) during hibernation. In contrast, under winter warming, the 3600-m-altitude lizard population primarily upregulated amino acid metabolism pathways (including serine and threonine metabolism; alanine, aspartate, and glutamate metabolism; cysteine and methionine metabolism; as well as histidine metabolism), which may be associated with cold stress adaptation. These findings contribute to our understanding of the adaptive effects of winter warming on reptiles and their physiological mechanisms, facilitating a better assessment of vulnerability to climate change.