Functional Ecology, Institute of Zoology, Universität Hamburg, Hamburg, Germany.
Proc Biol Sci. 2021 Jan 13;288(1942):20202059. doi: 10.1098/rspb.2020.2059.
Many tropical mammals are vulnerable to heat because their water budget limits the use of evaporative cooling for heat compensation. Further increasing temperatures and aridity might consequently exceed their thermoregulatory capacities. Here, we describe two novel modes of torpor, a response usually associated with cold or resource bottlenecks, as efficient mechanisms to counter heat. We conducted a field study on the Malagasy bat resting in foliage during the hot season, unprotected from environmental extremes. On warm days, the bats alternated between remarkably short micro-torpor bouts and normal resting metabolism within a few minutes. On hot days, the bats extended their torpor bouts over the hottest time of the day while tolerating body temperatures up to 42.9°C. Adaptive hyperthermia combined with lowered metabolic heat production from torpor allows higher heat storage from the environment, negates the need for evaporative cooling and thus increases heat tolerance. However, it is a high-risk response as the torpid bats cannot defend body temperature if ambient temperature increases above a critical/lethal threshold. Torpor coupled with hyperthermia and micro-torpor bouts broaden our understanding of the basic principles of thermal physiology and demonstrate how mammals can perform near their upper thermal limits in an increasingly warmer world.
许多热带哺乳动物对热很脆弱，因为它们的水分预算限制了蒸发冷却来补偿热量。进一步升高的温度和干旱可能会超过它们的体温调节能力。在这里，我们描述了两种新型的蛰伏模式，这是一种通常与寒冷或资源瓶颈相关的反应，作为对抗热量的有效机制。我们对马达加斯加蝙蝠进行了一项野外研究，发现它们在炎热的季节会栖息在树叶中，无法免受极端环境的影响。在温暖的日子里，蝙蝠在极短的微蛰伏和正常休息代谢之间交替，只需几分钟。在炎热的日子里，蝙蝠会在一天中最热的时候延长蛰伏时间，同时忍受高达 42.9°C 的体温。适应性高温与来自蛰伏的代谢热量产生降低相结合，允许从环境中储存更高的热量，无需蒸发冷却，从而提高了耐热性。然而，这是一种高风险的反应，因为蛰伏的蝙蝠如果环境温度升高超过临界/致死阈值，就无法控制体温。蛰伏与高温和微蛰伏相结合，拓宽了我们对热生理学基本原理的理解，并展示了哺乳动物如何在日益变暖的世界中接近其上限温度。
