State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, 100101 Beijing, China;
School of Biological Sciences, University of Aberdeen, AB24 3FX Aberdeen, Scotland, United Kingdom.
Proc Natl Acad Sci U S A. 2021 Jul 27;118(30). doi: 10.1073/pnas.2100707118.
The Qinghai-Tibetan Plateau, with low precipitation, low oxygen partial pressure, and temperatures routinely dropping below -30 °C in winter, presents several physiological challenges to its fauna. Yet it is home to many endemic mammalian species, including the plateau pika (). How these small animals that are incapable of hibernation survive the winter is an enigma. Measurements of daily energy expenditure (DEE) using the doubly labeled water method show that pikas suppress their DEE during winter. At the same body weight, pikas in winter expend 29.7% less than in summer, despite ambient temperatures being approximately 25 °C lower. Combined with resting metabolic rates (RMRs), this gives them an exceptionally low metabolic scope in winter (DEE/RMRt = 1.60 ± 0.30; RMRt is resting metabolic rate at thermoneutrality). Using implanted body temperature loggers and filming in the wild, we show that this is achieved by reducing body temperature and physical activity. Thyroid hormone (T and T) measurements indicate this metabolic suppression is probably mediated via the thyroid axis. Winter activity was lower at sites where domestic yak () densities were higher. Pikas supplement their food intake at these sites by eating yak feces, demonstrated by direct observation, identification of yak DNA in pika stomach contents, and greater convergence in the yak/pika microbiotas in winter. This interspecific coprophagy allows pikas to thrive where yak are abundant and partially explains why pika densities are higher where domestic yak, their supposed direct competitors for food, are more abundant.
青藏高原降水稀少、氧气分压低，冬季气温经常降至-30°C 以下，这对其动物群构成了多种生理挑战。然而，这里却是许多特有哺乳动物物种的家园，包括高原鼠兔。这些无法冬眠的小动物如何在冬季生存是一个谜。使用双标记水法测量每日能量支出 (DEE) 表明，鼠兔在冬季会抑制其 DEE。在相同的体重下，冬季的鼠兔消耗的能量比夏季少 29.7%，尽管环境温度低约 25°C。与静息代谢率 (RMR) 相结合，这使得它们在冬季的代谢范围非常低（DEE/RMRt = 1.60 ± 0.30；RMRt 是在热中性条件下的静息代谢率）。通过植入式体温记录仪和野外拍摄，我们发现这是通过降低体温和减少身体活动来实现的。甲状腺激素 (T 和 T) 的测量表明，这种代谢抑制可能是通过甲状腺轴介导的。在牦牛密度较高的地方，冬季的活动量较低。鼠兔通过食用牦牛粪便来补充这些地方的食物摄入，这通过直接观察、鼠兔胃内容物中牦牛 DNA 的鉴定以及冬季牦牛/鼠兔微生物群的更大趋同得到了证明。这种种间食粪行为使鼠兔在牦牛丰富的地方得以繁衍生息，这部分解释了为什么在牦牛密度较高的地方，鼠兔的密度更高，而牦牛是它们食物的直接竞争者。
