AsianScientist (Apr. 13, 2018) – Scientists in Japan have found that Japanese macaques (Macaca fuscata), also known as snow monkeys, bathe in hot springs to reduce stress from the cold weather. This behavior is associated with and has implications for social hierarchy and survival fitness. The findings are published in Primates.
Snow monkeys are the most northerly species of nonhuman primates in the world and have adapted to extremely cold winters. Researchers believed that the monkeys living in the Jigokudani Monkey Park in Nagano maintain their normal body temperature by growing thicker and longer fur during winter.
These primates are also the only group of monkeys known to take hot spring baths, a behavior that was first observed in 1963. For hygiene purposes, the park management has since built a hot spring for the exclusive use of the monkeys. By 2003, one in every three female monkeys in the group bathed regularly in winter.
In this study, a team of researchers led by Ms Rafaela Takeshita of Kyoto University in Japan has scientifically validated the benefits of the monkeys’ behavior. Although the fact that snow monkeys bathe more often during winter suggests that they use the hot spring to stay warm, there was a lack of physiological data to support this idea.
Takeshita and her colleagues studied twelve adult females during the spring birth season, from April to June, and winter mating season, from October to December. They determined how much time the monkeys spent in the hot springs, and which monkeys bathed the most.
The researchers also collected fecal samples during times of extreme cold and analyzed the concentration of fecal glucocorticoid (fGC) metabolite present. This was done because thermoregulatory stress and the management of a body temperature is known to influence concentrations of glucocorticoids, which belong to the family of steroid hormones.
The researchers confirmed that female snow monkeys use the hot spring more often in winter than in spring, and especially during colder weeks. Dominant female monkeys benefited from their status and took longer baths, but they were also involved in more aggressive conflicts, resulting in higher energy expenditure than subordinate female monkeys.
Furthermore, the researchers observed that taking baths in the hot spring reduced stress hormone levels in dominant female monkeys. The team thus deduced that a trade-off exists between the energetic cost of maintaining a high social status and access to hot spring baths. By dipping in the hot spring, dominant females lower their stress levels and conserve energy by reducing loss of body heat.
“This indicates that, as in humans, the hot spring has a stress-reducing effect in snow monkeys,” said Takeshita, who believes that further investigation using serum or saliva samples might be useful to detect whether there are any further short-term changes in stress levels. “This unique habit of hot spring bathing by snow monkeys illustrates how behavioral flexibility can help counter cold-climate stress, with likely implications for reproduction and survival.”
The article can be found at: Takeshita et al. (2018) Beneficial Effect of Hot Spring Bathing on Stress Levels in Japanese Macaques.
Source: Springer; Photo: Kento Mori.
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