Data from: Testing the heat dissipation limit theory in a breeding passerine

The maximum work rate of animals has recently been suggested to be determined by the rate at which excess metabolic heat generated during work can be dissipated (heat dissipation limitation theory; HDL). As a first step towards testing this theory in wild animals, we experimentally manipulated brood size in breeding marsh tits (Poecile palustris) to change their work rate. Parents feeding nestlings generally operated at above-normal body temperatures. Body temperature in both males and females increased with maximum ambient temperature and with manipulated work rate, sometimes even exceeding 45 °C, which is close to suggested lethal levels for birds. Such high body temperatures have previously only been described for birds living in hot and arid regions. Thus, reproductive effort in marsh tits may potentially be limited by the rate of heat dissipation. Females had lower body temperatures, a possible consequence of their brood patch serving as a thermal window facilitating heat dissipation. Because increasing body temperatures are connected to somatic costs, we suggest that the HDL theory may constitute a possible mediator of the trade-off between current and future reproduction. It follows that globally increasing, more stochastic, ambient temperatures may restrict the capacity for sustained work of animals in the future.近期有研究提出，动物的最大工作速率由其劳作过程中产生的过量代谢热的散逸速率决定（热散逸限制理论（Heat Dissipation Limitation theory, HDL））。为在野生动物中验证该理论，我们首先对繁殖期沼泽山雀（Poecile palustris）的窝雏数开展实验操控，以改变其抚育工作速率。育雏的亲鸟通常维持着高于正常水平的体温：无论雌雄，其体温均随最高环境温度与实验操控后的工作速率升高，有时甚至超过45℃，这一温度接近已报道的鸟类致死体温阈值。此前，这类超高体温仅在栖息于炎热干旱地区的鸟类中被观测到。由此可见，沼泽山雀的繁殖投入可能受限于热散逸速率。雌性亲鸟的体温更低，这可能源于其育雏斑作为热窗口促进了热量散逸。由于体温升高与躯体代价密切相关，我们认为热散逸限制理论或可成为当前繁殖与未来繁殖之间权衡关系的潜在介导因素。据此推测，全球范围内持续升高且愈发随机的环境温度，未来或会限制动物持续劳作的能力。