Data from: Divergence of thermal physiological traits in terrestrial breeding frogs along a tropical elevational gradient

Critical thermal limits are thought to be correlated with the elevational distribution of species living in tropical montane regions, but with upper limits being relatively invariant compared to lower limits. To test this hypothesis, we examined the variation of thermal physiological traits in a group of terrestrial breeding frogs (Craugastoridae) distributed along a tropical elevational gradient. We measured the critical thermal maximum (CTmax; n = 22 species) and critical thermal minimum (CTmin; n = 14 species) of frogs captured between the Amazon floodplain (250 m asl) and the high Andes (3800 m asl). After inferring a multi-locus species tree, we conducted a phylogenetically informed test of whether body size, body mass, and elevation contributed to the observed variation in CTmax and CTmin along the gradient. We also tested whether CTmax and CTmin exhibit different rates of change given that critical thermal limits (and their plasticity) may have evolved differently in response to different temperature constraints along the gradient. Variation of critical thermal traits was significantly correlated with species’ elevational midpoint, their maximum and minimum elevations, as well as the maximum air temperature and the maximum operative temperature as measured across this gradient. Both thermal limits showed substantial variation, but CTmin exhibited relatively faster rates of change than CTmax, as observed in other taxa. Nonetheless, our findings call for caution in assuming inflexibility of upper thermal limits, and underscore the value of collecting additional empirical data on species’ thermal physiology across elevational gradients.

学界普遍认为，临界热极限（critical thermal limits）与热带山地栖息物种的海拔分布格局存在关联，且相较于临界低温极限，临界高温极限相对恒定。为验证该假说，我们针对沿热带海拔梯度分布的陆生性繁殖蛙类（Craugastoridae）的热生理性状变异展开研究。我们测定了在亚马逊洪泛平原（海拔250米）至安第斯高地（海拔3800米）间捕获的蛙类的临界热最大值（critical thermal maximum, CTmax；n=22种）与临界热最小值（critical thermal minimum, CTmin；n=14种）。在构建多位点物种系统发育树后，我们采用系统发育校正分析，检验了体型大小、体质量及海拔因子是否对该海拔梯度上观测到的CTmax与CTmin变异存在贡献。鉴于临界热极限（及其可塑性）可能沿海拔梯度因温度约束差异而呈现不同的演化路径，我们同时检验了CTmax与CTmin的变化速率是否存在差异。研究结果显示，临界热性状的变异与物种的海拔中点、最高与最低海拔，以及该梯度下测得的最高气温与最高有效温度均存在显著关联。两类热极限均表现出显著变异，但与其他类群的观测结果一致，CTmin的变化速率相对快于CTmax。尽管如此，本研究结果提示，在假设高温热极限缺乏可塑性时需保持审慎，同时也凸显了在海拔梯度上收集更多物种热生理相关实测数据的重要价值。