Quantifying the costs of mating is key for understanding life-history trade-offs. As a reflection of metabolic rate, body temperature is one metric for assaying these costs. However, conventional methods for measuring body temperature are invasive and unsuitable for the study of free-living populations of endangered species, including great apes. A promising proxy for body temperature is fecal temperature, the internal temperature of fecal deposits shortly following defecation. We validated this method with humans, finding that maximum fecal temperature is a reliable proxy for rectal temperature. We then applied this method to wild chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda. We collected and analyzed 101 fecal temperature measurements from 43 adult chimpanzees (male: N = 28; female: N = 15). Chimpanzee fecal temperature ranged from 33.4 to 38.9 °C, with a mean of 35.8 °C. Although fecal temperature was not predicted by sex, age, or ambient temperature, male fecal temperature was 1.1 °C higher on days when sexually receptive females were present and was positively correlated with male dominance rank. Post hoc analyses showed that overall copulation rates, but not aggression rates, were positively correlated with fecal temperature, suggesting that sexual physiology and behavior best explain mating-related temperature variation. Together, these results indicate fecal temperature is a reliable proxy for core body temperature in large-bodied mammals, captures metabolic costs associated with male mating behavior, and represents a valuable noninvasive tool for biological field research. Body temperature illuminates an animal’s physiological condition and energy expenditure, but it is difficult to measure in wild animals. Consequently, basic data on body temperature and its socioecological correlates in wild animals are scant, especially when noninvasive measures must be used. To address this problem, we demonstrated that the temperatures of fecal deposits reliably estimate body temperatures in a large bodied primate and are approximately as reliable as invasive, subcutaneous transponder methods used in other mammals. We then found that fecal temperature in chimpanzees varied by ecologically and reproductively relevant variables including time of year, the presence of sexually receptive females, and dominance rank. Sexual behavior was likely responsible for increased male fecal temperature, as overall copulation frequency, but not aggression, was correlated with fecal temperature. We therefore provide evidence that fecal temperature can be used to assay body temperature and address questions regarding physiological condition and metabolic expenditure.

中文翻译：

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优势等级和接受性行为的雌性的存在可以预测雄性黑猩猩粪便测量的体温


量化交配成本是理解生活史权衡的关键。作为新陈代谢率的反映，体温是衡量这些成本的指标之一。然而，测量体温的传统方法具有侵入性，不适合研究包括类人猿在内的濒危物种的自由生活种群。粪便温度是体温的一个有希望的指标，即排便后不久粪便沉积物的内部温度。我们对人类验证了这种方法，发现最高粪便温度是直肠温度的可靠指标。然后，我们将这种方法应用于乌干达基巴莱国家公园 Ngogo 的野生黑猩猩 (Pan troglodytes schweinfurthii)。我们收集并分析了 43 只成年黑猩猩（雄性：N = 28；雌性：N = 15）的 101 次粪便温度测量值。黑猩猩粪便温度范围为 33.4 至 38.9 °C，平均为 35.8 °C。尽管粪便温度不能通过性别、年龄或环境温度来预测，但在有性行为的雌性存在的日子里，雄性粪便温度要高出 1.1 °C，并且与雄性优势等级呈正相关。事后分析表明，总体交配率（而非攻击率）与粪便温度呈正相关，这表明性生理和行为最好地解释了与交配相关的温度变化。总之，这些结果表明粪便温度是大型哺乳动物核心体温的可靠指标，捕获与雄性交配行为相关的代谢成本，并代表了生物领域研究的宝贵非侵入性工具。体温可以反映动物的生理状况和能量消耗，但在野生动物中很难测量。 因此，有关野生动物体温及其社会生态相关性的基本数据很少，特别是在必须使用非侵入性措施时。为了解决这个问题，我们证明粪便沉积物的温度可以可靠地估计大型灵长类动物的体温，并且与其他哺乳动物中使用的侵入性皮下应答器方法大致一样可靠。然后我们发现黑猩猩的粪便温度随生态和生殖相关变量的变化而变化，包括一年中的时间、接受性行为的雌性的存在以及优势等级。性行为可能是导致雄性粪便温度升高的原因，因为总体交配频率（而非攻击行为）与粪便温度相关。因此，我们提供证据表明粪便温度可用于测定体温并解决有关生理状况和代谢消耗的问题。