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.

长期以来，学界普遍认为临界热限（critical thermal limits）与热带山地物种的海拔分布格局存在关联，且相较于临界热下限而言，临界热上限相对恒定。为验证这一假说，我们对沿热带海拔梯度分布的一类陆栖繁殖蛙类（Craugastoridae科）的热生理性状变异情况展开了研究。我们测定了在亚马逊洪泛平原（海拔250米）至安第斯高海拔区域（海拔3800米）间捕获的蛙类的临界热最大值（critical thermal maximum, CTmax，样本量覆盖22个物种）与临界热最小值（critical thermal minimum, CTmin，样本量覆盖14个物种）。在构建多基因座物种树之后，我们开展了基于系统发育关系的检验，以分析体型大小、体质量及海拔是否对沿该海拔梯度观测到的CTmax与CTmin变异存在贡献。此外，我们还检验了CTmax与CTmin的变化速率是否存在差异——鉴于沿该梯度分布的不同温度约束条件，可能使得临界热限（及其可塑性）的演化路径有所不同。研究结果显示，临界热性状的变异与物种的海拔分布中点、最大与最小海拔分布范围，以及该梯度下测得的最高气温与最高有效温度（operative temperature）均存在显著相关性。两类热限均表现出显著变异，且正如其他生物类群所观测到的那样，CTmin的变化速率相对快于CTmax。尽管如此，我们的研究结果提示，在假设临界热上限具有不可变性时应保持审慎态度，同时也强调了在海拔梯度上收集更多物种热生理学实证数据的重要价值。