The Beatles sang “I get by with a little help from my friends.” It’s probably just as well that their American imitators, The Monkees, didn’t try for a scientifically accurate counterpart, because singing about the benefits of friendship for one’s gut microflora probably has limited commercial appeal.
Whatever its lyrical limitations, however, the discovery that sociable rhesus macaques (Macaca mulatta) have a healthier ecosystem in their digestive tract could have a number of important implications. The macaques demonstrate that strong social networks not only increase healthy intestinal bacteria, but they surprisingly also reduce the abundance of unhealthy varieties.
Dr Katerina Johnson of the University of Oxford and co-authors draw these conclusions in a paper published in Frontiers in Microbiology, using fecal samples from macaques on Cayo Santiago, a small island off Puerto Rico. The macaques originate in Asia but have thrived in the absence of predators since being transported to the island in 1938. With such a small island and little fear, the population there is easy to study, while still living in communities closer to the wild than zoo populations.
The samples were compared with observations of how much time donor monkeys spent grooming each other and how many grooming partners each monkey had. “We show that more sociable monkeys have a higher abundance of beneficial gut bacteria, and a lower abundance of potentially disease-causing bacteria,” Johnson said in a statement.
A 2020 review, with overlapping authors, reported sociable baboons have more diverse gut ecosystems. Presumably getting close enough to a fellow member of your species to groom them provides opportunities to swap intestinal bacteria, although it may be best not to think about it too much.
Consequently, it’s no surprise that macaques with the strongest grooming networks are more likely to have Faecalibacterium and Prevotella in their stool samples. “Faecalibacterium is well known for its potent anti-inflammatory properties and is associated with good health,” Johnson said. Moreover, these bacteria are less abundant in people with autism, and in rodents with autism-like symptoms.
This raises questions of cause and effect. Does a beneficial bacteria deficit contribute to some of the negative aspects of autism, or is it the other way round? Since children with autism are frequently, although not universally, more socially disconnected than neurotypicals, might they have fewer opportunities to collect good bacteria from playmates?
Johnson and co-authors suggest both may be occurring, referring to the relationship between sociability and beneficial bacteria in the monkeys as “reciprocal”. There “could also be an indirect effect, as monkeys with fewer friends may be more stressed, which then affects the abundance of these microbes,” Johnson added.
A more puzzling aspect of the findings is that sociable macaques are actually less likely to have Streptococcus, the cause of “strep throat” and pneumonia, in their guts. Reduced social interactions are normally protective against pathogen infections, so the finding is unusual, but Johnson told IFLScience; The differential abundance of Streptococcus may reflect an indirect effect as we know friendships are very good at buffering against stress and stress is known to negatively affect the gut microbial community."
In this context low sociability may appear so harmful it is surprising it can survive evolutionary pressure at all. However, Johnson told IFLScience; " Individuals that are less sociable may have better traits in other domains which may help explain why variation in sociable behaviour persists."
The study combines Johnson’s diverse research interests. She’s previously demonstrated feedback loops between the dominant gut bacteria and dietary preferences, while her work on sociability in animals has confirmed birds prefer to nest close to those with similar personalities.
Senior author Professor Robin Dunbar, famous for his work on social network size, noted the findings are increasingly relevant, saying: “As our society is increasingly substituting online interactions for real-life ones, these important research findings underline the fact that as primates, we evolved not only in a social world but a microbial one as well.”
The paper is open access at Frontiers in Microbiology.