Popular girls are always well groomed - even in the monkey world. Thanks to all the extra grooming, high-ranking female macaques never have to worry about lice, according to a new study on animal behavior.
However, popularity comes at a price. Researchers found that high-ranking macaques were more likely to contract infections because they came in contact with more individuals.
Researchers from Japan's University of Kyoto observed lice egg-picking behavior in macaques to see if social rank influenced the amount of lice each individual carried.
"We thought that, since grooming is one of the most common types of contact that occurs between macaques, this behavior should facilitate the transmission of lice," said lead author Julie Duboscq, who conducted the research at France's University of Strasbourg and is currently based at Kyoto University. "At the same time, grooming might also constrain the spread of lice because louse eggs are removed during grooming, which reduces future generations of lice."
Researchers observed egg-picking behavior of a group of Japanese macaques living on the Koshima islet of the Miyazaki prefecture for five months. Duboscq and her team were able to build a model of the groups social network by recording who was grooming whom and how often. Building the social network model was important because it helped researchers distinguish high-ranking from low-ranking individuals.
The findings revealed that high-ranking females who were most central to the group had significantly less lice than lower-ranking macaques. Researchers found that this was especially true during the winter and summer months when lice burden was particularly high. They explained that macaques mate in the winter and give birth in the summer.
It's not all peaches and cream for these socialite macaques though. High-ranking macaques were most likely to receive grooming from other individuals, but they also had the highest risk of infection and disease.
"The link between sociality and parasitism is not always straightforward," said senior author Andrew MacIntosh, a researcher at Kyoto University's Primate Research Institute. "Increased centrality in social networks is often linked to increased parasite load and disease risk."
"For this study, however, interactions between environmental seasonality and both parasite and host biology appeared to mediate the role of social processes in louse burdens," MacIntosh added.
"Our study shows that variation in contact and grooming network centrality in terms of number of connections explains variation in lice load in female Japanese macaques in that less central females have higher lice burden, providing further evidence of grooming as an efficacious anti-parasite strategy," researchers concluded.
The study was published in the journal Scientific Reports.
