To maintain constant body temperature ( T b ) over a wide range of ambient temperatures ( T a ) endothermic animals require large amounts of energy and water. In hot environments, the main threat to endothermic homeotherms is insufficient water to supply that necessary for thermoregulation. We investigated flexible adjustment of traits related to thermoregulation and water conservation during acclimation to hot conditions or restricted water availability, or both, in the zebra finch, Taeniopygia guttata a small arid-zone passerine. Using indirect calorimetry, we measured changes in whole animal metabolic rate (MR), evaporative heat loss (EHL) and T b before and after acclimation to 23 or 40 °C, with different availability of water. Additionally, we quantified changes in partitioning of EHL into respiratory and cutaneous avenues in birds exposed to 25 and 40 °C. In response to heat and water restriction zebra finches decreased MR, which together with unchanged EHL resulted in increased efficiency of evaporative heat loss. This facilitated more precise T b regulation in heat-acclimated birds. Acclimation temperature and water availability had no effect on the partitioning of EHL into cutaneous or respiratory avenues. At 25 °C, cutaneous EHL accounted for ~ 60% of total EHL, while at 40 °C, its contribution decreased to ~ 20%. Consistent among-individual differences in MR and EHL suggest that these traits, provided that they are heritable, may be a subject to natural selection. We conclude that phenotypic flexibility in metabolic heat production associated with acclimation to hot, water-scarce conditions is crucial in response to changing environmental conditions, especially in the face of current and predicted climate change.

中文翻译：

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斑胸草雀（一种小型干旱区雀斑）对热和水适应的产热和热损失的表型灵活性

为了在很宽的环境温度 (T a ) 范围内保持恒定的体温 ( T b )，吸热动物需要大量的能量和水。在炎热的环境中，吸热恒温的主要威胁是没有足够的水来供应体温调节所需的水。我们研究了在斑胸草雀 Taeniopygia guttata 一种小型干旱区雀科动物适应炎热条件或有限的可用水量或两者兼而有之的过程中，对与温度调节和节水相关的性状的灵活调整。使用间接量热法，我们测量了整个动物代谢率 (MR)、蒸发热损失 (EHL) 和 Tb 在适应 23 或 40 °C 前后的变化，水的可用性不同。此外，我们量化了暴露于 25°C 和 40°C 的鸟类中 EHL 分配到呼吸和皮肤途径的变化。作为对热量和水分限制的响应，斑胸草雀降低了 MR，这与 EHL 不变一起导致蒸发热损失效率增加。这促进了热适应鸟类中更精确的 T b 调节。适应温度和水的可用性对 EHL 分为皮肤或呼吸途径没有影响。在 25 °C 时，皮肤 EHL 占总 EHL 的约 60%，而在 40 °C 时，其贡献下降至约 20%。MR 和 EHL 的个体间一致差异表明这些性状，只要它们是可遗传的，就可能受自然选择的影响。我们得出结论，代谢产热的表型灵活性与适应炎热有关，