Phylogenetic tree used in the phylogenetic analyses 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 evaluated 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 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，学界已提出多种补偿机制假说，用以阐释变温动物（ectothermic animals）如何应对环境温度（T_A）随纬度升高而降低的现象。其中一项名为‘代谢内稳态假说’（metabolic homeostasis hypothesis, MHH）的假说指出，物种在其自然分布范围内所经历的环境温度区间的低温端，其标准代谢率温度系数Q10（Q10-SMR）应达到最高水平。据此逻辑，物种可在当日低温时段最小化维持代谢的能量成本，并在气温回暖时段快速利用环境温度升高带来的有利条件。
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，所有数值均在四个温度区间内测定完成，用于验证代谢内稳态假说衍生出的三项预测。研究结果与该假说相符：（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定的Q10-SMR值更高，而热带物种在较高环境温度下测定的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。
本研究首次证实，变温动物的Q10-SMR与纬度的关联关系会因Q10-SMR的测定环境温度而异，这与适应性假说的预测一致。本文隶属于主题专辑‘Physiological diversity and global patterns of biodiversity in a time of global climate change: testing and generating key hypotheses involving temperature and oxygen’。