Snow monkeys don’t just bathe in Japan’s hot springs because it helps them to stay warm. It seems to be good for their health too.
Research in the journal Primates reveals that bathing changes the microorganisms that live in and on the photogenic macaques.
Japanese macaques, known colloquially as snow monkeys, are the most northerly-dwelling species of non-human primate.
They live in the mountainous regions of Japan, where the winters are bitter and the snow is deep. Thick fur provides insulation, but many monkeys take advantage of the steamy geothermal springs, where they huddle together and socialise for hours at a time.
There’s more to it than that, however. Researchers from Kyoto University travelled to the Jigokudani Monkey Park in central Japan’s Nagano prefecture on Honshu Island. Over two consecutive winters, they monitored a group of female macaques, made up of nine bathers and seven non-bathers.
They monitored the monkeys’ nit-picking behaviour and collected faecal samples, which were analysed to give a snapshot of the microorganisms living in their guts.
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Bathers and non-bathers picked nits from different locations on their bodies, suggesting that the hot water has an effect on the behaviour and egg-laying of the lice that trouble them.
And whilst the overall diversity of gut microbes was similar between the two groups, several types of bacteria were more abundant in non-bathing individuals compared with bathers. This included Fusobacterium and Acinetobacter, which are varieties of bacteria that have been linked to different infections in humans. Their role in macaques is currently unclear.
“Hot spring bathing is one of the most unusual behaviours seen in nonhuman primates,” says researcher Abdullah Langgeng. “Behaviour is often treated as a response to the environment, but our results show that this behaviour doesn’t just affect thermoregulation or stress: it also alters how macaques interact with parasites that live on and inside them.”
The study enabled the researchers to test the idea that bathing alters the holobiont. This is the integrated biological system made up of the host and all of its associated microorganisms. Bathing did affect the holobiont, but the shifts were subtle.
Whilst gut microbes and the distribution of lice were affected, internal parasites were not. Bathers were no more likely than non-bathers to suffer from internal parasites. This comes as a relief, because there have been concerns that shared bathing could make it easier for internal parasites to spread.
In pictures: bathing snow monkeys
Top image: Japanese macaques in hot spring. Credit: Getty
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