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 (Ochotona curzoniae). 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 (T3 and T4) measurements indicate this metabolic suppression is probably mediated via the thyroid axis. Winter activity was lower at sites where domestic yak (Bos grunniens) 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.

Brandt's voles Lasiopodomys brandtii exhibit large increases in nonshivering thermogenesis to cope with chronic cold exposure, resulting in compensatory hyperphagia and fat mobilization. These physiological events are accompanied by a remarkable reduction in serum leptin levels. However, the role of hypoleptinemia in cold adaptation in this species is still unknown. In the present study, we tested the hypothesis that hypoleptinemia contributes to increases in food intake and brown adipose tissue (BAT) thermogenesis by modifying hypothalamic neuropeptides in cold-exposed Brandt's voles. Adult male voles were transferred to 5°C for 28 days. Accompanied by a decrease in serum leptin levels, hypothalamic agouti-related protein (AgRP) mRNA levels were significantly increased, but there were no changes in the long form of leptin receptor (Ob-Rb), suppressor of cytokine signaling 3 (SOCS3), neuropeptide Y (NPY) mRNA, proopiomelanocortin (POMC), and cocaine-and amphetamine-regulated peptide (CART) mRNA levels in the hypothalamus. When coldexposed voles were returned to warm (23°C) for 28 days, body mass, food intake, serum leptin, and AgRP mRNA were restored to control levels. Leptin administration in cold-exposed voles decreased food intake as well as hypothalamic AgRP mRNA levels. There were no significant effects of leptin administration on hypothalamic Ob-Rb, SOCS3, NPY, POMC, CART mRNA, and uncoupling protein 1 levels under cold conditions. These results suggest that hypoleptinemia partially contributes to cold-induced hyperphagia, which might involve the elevation of hypothalamic AgRP gene expression. cold exposure; leptin administration; neuropeptide SMALL ENDOTHERMIC MAMMALS inhabiting temperate and arctic regions exhibit extraordinary physiological adaptations to harsh winter to ensure their survival (31,43,45). Brandt's vole (Lasiopodomys brandtii), which mainly inhabits the Inner Mongolia grasslands of China, Mongolia, and the Baikal region of Russia, where winter lasts for Ͼ 5 mo. In the Xilin River Valley, a major habitat of Brandt's vole in Inner Mongolia, the lowest temperature is Ϫ47.5°C (11). In winter, Brandt's vole decrease body mass (25) and cease reproduction (26,27,44). During cold exposure (4 -5°C), captive Brandt's voles met most of their energy demand not only by increasing food intake, but also by mobilizing body fat (24, 48). The increase in food intake and the decrease in body fat are closely related with circulating leptin levels, which decreased by 52% under cold acclimation (48). However, the role of hypoleptinemia during cold adaptation in this species is still not known.Peptidergic neurons within the hypothalamus produce a number of neuropeptides, which can be divided into two categories: 1) orexigenic neuropeptides, such as neuropeptide Y (NPY) and agouti-related protein (AgRP), which can stimulate food intake and inhibit energy expenditure, and 2) anorectic neuropeptides, such as proopiomelanocortin (POMC) and cocaine-and amphetamine-regulated peptide (CART), which can inhibit food int...