Golden Snub-nosed Monkeys Rhinopithecus roxellana live in high altitude temperate forests, where winter temperatures commonly drop below 0°C, and approximately 50 cm of snow covers the ground for several weeks in the winter. These cold periods impose significant thermoregulatory energetic challenges for these animals. To better understand the adaptations that enable these monkeys to live and thrive in such a harsh environment, scientists tested if they change their food choice in cold periods to specifically select the additional levels of fat and carbohydrate needed to fuel the additional costs of temperature regulation in winter. This is not an easy task when studying free-ranging animals, but the study system provided a unique set of circumstances that enabled this test to be made.

Golden Snub-nosed Monkey in cold winter. Copyright: Prof. David Raubenheimer

The study aims were accomplished by provisioning the study population with a surplus of the same supplementary foods in winter and spring. Individually-recognisable monkeys were followed and their diet choices recorded in detail, samples of all foods they ate were analysed for their nutritional content to calculate diet nutrient composition and thermal imaging photographs (to calculate the additional energy used in winter compared with spring) were analysed.

The collected data were analyzed using nutritional geometry, a multidimensional framework that explores how animals balance the ingestion of multiple nutrients. The study results showed that in winter the monkeys ate twice as much energy compared to spring, and did so specifically by eating more fats and carbohydrates (which are used to generate heat), while protein intake remained the same. This seasonal difference in energy intake matched closely the seasonal difference in the daily energetic costs of thermoregulation.

The results not only show that Golden Snub-nosed Monkeys forage selectively to balance the macronutrient content of their diet, but they also change the balance selected to meet changes in the nutrients needed, in this case for generating body heat. These results have important implications for understanding how Golden Snub-nosed Monkeys respond to temperature changes, including those experienced through global warming, and how these responses might influence broader aspects of the ecology upon which they rely.

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Reference:

Song-Tao Guo, Rong Hou, Paul. A. Garber, David Raubenheimer, Nicoletta Righini, Wei- Hong Ji, Ollie Jay, Shu-Jun He, Fan Wu, Fang-Fang Li, Bao-Guo Li (2018) Nutrient-specific compensation for seasonal cold stress in a free-ranging temperate colobine monkey. Functional Ecology 2018:1-11