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Monkeys Snub Protein to Keep Warm in Winter

Credit: David Raubenheimer

University of Sydney researchers have found that golden snub-nosed monkeys living in cold, snowy habitats adjust their nutrient intake to match the elevated costs of thermo­regulation, with fats and carbohydrates taking precedence over proteins.

The study, published in Functional Ecology (https://goo.gl/Hx3DTj), was conducted in China’s Quinling mountains, where winter temperatures commonly drop below 0°C and approximately 50 cm of snow covers the ground for several weeks in the winter.

The researchers analysed the foods that monkeys consumed in order to calculate the nutrient composition of their diets, and then assessed the additional energy the monkeys used to regulate their temperature in winter compared with spring.

“To better understand the adaptations that enable these monkeys to live and thrive in such a harsh environment – among the coldest for any primate – we tested how they cope with additional energetic costs of keeping warm in winter,” said Prof David Raubenheimer, who conducted the study’s nutritional modelling.

“Our study controlled for food availability using supplementary foods to ensure that food was abundant throughout the year and the amounts eaten in winter and spring were due to the animals’ own choices rather than ecological restrictions on what was available to eat.

“The monkeys ate twice as much energy in winter compared to spring. Remarkably, the additional intake in winter came entirely from fats and carbohydrates, with protein intake remaining the same.”

“Winter was shown to impose significant thermo­regulatory energetic challenges for these animals,” said co-author A/Prof Ollie Jay. “Using thermal imaging photographs, we measured the monkeys’ surface temperature at specific points on their bodies. Taking into account additional factors such as wind speed and environmental temperature, these measures were used to calculate heat lost from the body.”

The seasonal difference in energy intake closely matched the seasonal difference in the daily energetic costs of thermo­regulation. “Amazingly, we found that the additional heat lost by monkeys in winter compared with spring almost exactly matched the additional energy they ate in winter in the form of fats and carbs,” Raubenheimer said. “This provides strong evidence golden snub-nosed monkeys forage selectively to balance the macronutrient content of their diet, but also change the balance to meet changes in the nutrients needed – in this case for generating body heat.

“A helpful way to think about this is from the other direction – the monkeys ate half the fats and carbs in spring compared to winter. Since foods were available for them also to have high fat and carb intake in spring, and yet they abstained, this shows that they balance their nutrient intake to meet specific nutritional needs.

“It also raises significant questions about another species of primate that clearly does not manage its intake quite so well – our own species,” Raubenheimer said.