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.现有研究普遍认为，热带山地物种的临界热极限（critical thermal limits）与其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，我们对沿热带海拔梯度分布的一类陆栖繁殖蛙类（Craugastoridae）的热生理性状变异展开研究。我们测定了在亚马逊泛滥平原（海拔250米）与安第斯高海拔区域（海拔3800米）间捕获的蛙类的临界高温上限（critical thermal maximum，CTmax；n=22种）与临界低温下限（critical thermal minimum，CTmin；n=14种）。在构建多基因座物种树后，我们开展了纳入系统发育关系的统计检验，以探究体型、体质量及海拔是否对沿该海拔梯度分布的蛙类CTmax与CTmin的变异存在贡献。鉴于临界热极限（及其表型可塑性）可能沿海拔梯度因温度限制的差异而经历了不同的演化路径，我们同时检验了CTmax与CTmin的变化速率是否存在差异。临界热性状的变异与物种的海拔中点、其分布的最高与最低海拔，以及该梯度内测得的最高气温与最高有效温度（operative temperature）显著相关。两类热极限均存在显著变异，但正如其他类群中观测到的结果，CTmin的变化速率相对快于CTmax。尽管如此，本研究结果表明，在假设高温热极限具有固定不变的稳定性时需保持谨慎，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性。