Scripts used in R from Testing the metabolic homeostasis hypothesis in amphibians.

A number of hypotheses about compensatory mechanisms that allow ectothermic animals to cope with the latitudinal decrease in ambient temperature (<i>T</i>_A) have been proposed during the last century. One of these hypotheses, the ‘metabolic homeostasis’ hypothesis (MHH), states that species should show the highest thermal sensitivity of the metabolic rate (<i>Q</i>_10-SMR) at the colder end of the range of <i>T</i>_As they usually experience in nature. This way, species should be able to minimize maintenance costs during the colder hours of the day, but quickly take advantage of increases in <i>T</i>_A during the warmer parts of the day. Here, we created a dataset that includes <i>Q</i>_10-SMR values for 58 amphibian species, assessed at four thermal ranges, to evaluate three predictions derived from the MHH. In line with this hypothesis, we found that: (i) <i>Q</i>_10-SMR values tended to be positively correlated with latitude when measured at lower <i>T</i>_As, but negative correlated with latitude when measured at higher <i>T</i>_As, (ii) <i>Q</i>_10-SMR measured at lower <i>T</i>_As were higher in temperate species, whereas <i>Q</i>_10-SMR measured at higher <i>T</i>_As were higher in tropical species, and (iii) the experimental <i>T</i>_A at which <i>Q</i>_10-SMR was maximal for each species decreased with latitude. This is the first study to our knowledge showing that the relationship between <i>Q</i>_10-SMR and latitude in ectotherms changes with the <i>T</i>_A at which <i>Q</i>_10-SMR is assessed, as predicted from an adaptive hypothesis.This article is part of the theme issue ‘Physiological diversity and global patterns of biodiversity in a time of global climate change: testing and generating key hypotheses involving temperature and oxygen’.

近一个世纪以来，学界已提出多项关于变温动物（ectothermic animals）应对环境温度（ambient temperature，记为T_A）随纬度梯度降低的补偿机制假说。其中一项名为“代谢内稳态假说”（metabolic homeostasis hypothesis，MHH）的假说指出：物种在其自然生存所经历的环境温度区间的低温端，应表现出最高的代谢率热敏感性——即标准代谢率的温度系数Q₁₀-SMR（Q₁₀-SMR）。据此逻辑，物种可在每日低温时段最小化维持代谢成本，并在日间温暖时段快速借助环境温度升高获益。

本研究构建了一份数据集，涵盖58个两栖动物物种的Q₁₀-SMR值，所有指标均在四个温度区间下测定，用于验证由MHH推导得到的三项预测。本研究结果符合该假说的预期：（1）在较低环境温度下测定的Q₁₀-SMR值与纬度呈正相关，而在较高环境温度下测定的Q₁₀-SMR值则与纬度呈负相关；（2）温带物种在较低环境温度下测得的Q₁₀-SMR值更高，而热带物种在较高环境温度下测得的Q₁₀-SMR值更高；（3）各物种Q₁₀-SMR达到最大值时对应的实验环境温度，随纬度升高而降低。据我们所知，本研究首次证实：变温动物的Q₁₀-SMR与纬度之间的关联，会因Q₁₀-SMR测定时所处的环境温度而发生变化，这与适应性假说的预测完全一致。

本文属于专题刊《全球气候变化时代下的生理多样性与生物多样性全球格局：检验与构建涉及温度与氧气的关键假说》（Physiological diversity and global patterns of biodiversity in a time of global climate change: testing and generating key hypotheses involving temperature and oxygen）的一部分。