STRASBOURG, France, March 11 (UPI) -- For many monkeys, grooming is an act of both hygiene and socialization -- a way to maintain health and social hierarchies.
New research shows those at the top of the social hierarchy -- the most popular monkeys -- tend to benefit the most from communal hygiene. Scientists in France and Japan determined female Japanese macaques with the most friends had fewer lice than their less popular peers.
"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," biologist Julie Duboscq said in a news release. "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."
Duboscq led the research while serving at the University of Strasbourg in France, but now conducts his research at Kyoto University in Japan.
After monitoring grooming behavior and socialization among a group of female macaques, Duboscq and her colleagues built a model to predict which females hosted the fewest lice and which enjoyed the most social interactions.
Their calculations determined the most popular females were best able to avoid lice infestations. The hygienic benefits of their popularity was most prevalent during the times of year when females are most physically active -- during the mating and birthing seasons.
"The link between sociality and parasitism is not always straightforward," said senior study 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."
Previous studies showed the most popular females were more vulnerable to intestinal worms.
"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 said.
The new research was published in the Scientific Reports.