Japanese Monkeys Like to Socialize, Even With Nits to Pick
Social life is good for you, even when your friends have lice — if you’re a Japanese macaque.
Whether the same is true for humans hasn’t been tested directly, at least not the way researchers in Japan conducted their experiments with networks of female macaques.
Julie Duboscq, a researcher at Kyoto University’s Primate Research Institute in Japan, tracked louse infestation and grooming interactions in about 20 adult female macaques. As she, Andrew J.J. MacIntosh and their colleagues noted in describing their research in Scientific Reports, grooming is known to reduce lice, but such close physical contact can also make it easy for lice to pass from one animal to another.
日本京都大学灵长类研究所(Primate Research Institute)的研究员朱莉·迪博斯克(Julie Duboscq)追踪了大约20头成年母猕猴当中的虱子滋生现象与梳毛行为的互动。在发表于《科学报告》(Scientific Reports)的文章中，她和安德鲁·J·J·麦金托什(Andrew J.J. MacIntosh)及几名同事指出，外界已知梳毛行为可减少虱子，但此类亲密的身体互动也会让虱子更容易地从一只猕猴传到另一只身上。
Dr. Duboscq is interested in the costs and benefits of social behavior. For animals that live in social groups, as macaques and people do, the benefits of social life are many, from defense against predators (for wild monkeys, and no doubt for humans at some point in their history) to emotional health and well-being (for humans, and probably monkeys, too).
But there are negatives associated with sociality, like the transmission of parasites and diseases. “We don’t fully understand the costs and benefits,” Dr. Duboscq said.
In this study, she and her colleagues estimated the degree of louse infestation by the number of nits picked. The more nits, they calculated, the more lice-producing nits.
They compared the degree of louse infestation with how central each female was in the social network, meaning how many other monkeys were her social contacts. The result was that the females with more social contacts, and who therefore received more grooming, had fewer lice, but only during the winter and summer.
During the spring and fall, a female’s position in a social network didn’t seem to make any difference.
Dr. Duboscq said the reason for the seasonal difference wasn’t yet clear, but it was possible that the monkeys’ biology affected that of the lice.
Winter is the mating season for these macaques, and they give birth in the summer. Hormonal changes in the blood of the macaques that the lice feed on could affect louse reproduction and cause a jump in lice in winter and summer, which would make grooming more important.
But that is only speculation so far. What is clear is that grooming works well to keep the louse population down. In this case, the benefits of sociality outweigh the risks.