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，热带山地物种的临界热极限与其海拔分布存在相关性，且相较于热耐受下限，热耐受上限相对恒定。为验证该假说，我们针对沿热带海拔梯度分布的卵齿蟾科（Craugastoridae）陆栖繁殖蛙类的热生理性状变异展开研究。我们测定了采集自亚马逊泛滥平原（海拔250米）与安第斯高地（海拔3800米）之间的蛙类的临界最高热耐受温度（CTmax；n=22种）与临界最低热耐受温度（CTmin；n=14种）。在构建多基因座物种系统发育树后，我们采用系统发育校正分析，检验了体型、体质量以及海拔是否对沿该梯度观测到的CTmax与CTmin变异存在贡献。此外，鉴于临界热极限（及其可塑性）可能沿梯度因温度约束差异而演化路径不同，我们还检验了CTmax与CTmin的变化速率是否存在差异。研究结果显示，临界热生理性状的变异与物种的海拔中点、最高与最低海拔，以及该梯度内测定的最高气温与最高有效温度均存在显著相关性。两类热极限均存在显著变异，但正如其他类群的观测结果，CTmin的变化速率相对更快。尽管如此，本研究结果表明，在假设热耐受上限具有不可变性时需保持谨慎，同时也凸显了跨海拔梯度收集物种热生理相关实证数据的重要价值。