Having good friendships can create a healthier gut microbiome

Social connections are essential for good health and well-being in social animals like us and other primates. There is also growing evidence that the gut microbiome – through the so-called “gut-brain axis” – plays a key role in our physical and mental health, and that bacteria can be socially transmitted, for example through touch.

So how does social connectedness translate to the composition and diversity of the gut microbiome? This is the subject of a new study in Frontiers in Microbiology in rhesus macaques (Macaca mulatta).

Lead author Dr. Katerina Johnson, research associate in the Department of Experimental Psychology and the Department of Psychiatry at the University of Oxford, said: “Here we show that more social monkeys have higher abundances of beneficial gut bacteria and lower abundances of potentially disease-causing bacteria.”

Monkey Island

The scientists focused on a single social group (with 22 males and 16 females between the ages of six and 20) of rhesus macaques on the island of Cayo Santiago, off the east coast of Puerto Rico. Macaques originally lived only in North Africa and Asia. But in 1938, a founding population of 409 rhesus macaques was brought from India to Cayo Santiago. Today, more than 1,000 macaques live on the 15.2-hectare island, divided into different social groups. They roam and forage freely, although their diet is supplemented daily with monkey chow. Researchers make behavioral observations of the monkeys every year.

Between 2012 and 2013, the authors collected a total of 50 uncontaminated stool samples from this social group. As a measure of social connectedness, they used the time each monkey spent grooming or being groomed in 2012 and 2013, and the number of mates he or she had.

Social grooming

Co-author Dr. Karli Watson, from the Cognitive Science Institute at the University of Colorado Boulder, explained: “Macaques are highly social animals, and grooming is their primary way of establishing and maintaining relationships, so grooming provides a good indicator of social interactions.”

Johnson, Watson and their team analyzed DNA sequence data from the stool samples to measure the composition and diversity of the gut microbial community and examined the relationship with social connectedness. They also took into account gender, age, season and rank in the team hierarchy. They focused on microbes that have been repeatedly shown to be either more or less abundant in humans or in rodents with autism-like symptoms (usually accompanied by social withdrawal) or that are socially deprived.

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Social monkeys have more “good” microbes

“Engagement in social interactions was positively associated with the abundance of certain gut microbes with beneficial immune functions and negatively with the abundance of potentially pathogenic members of the microbiota,” said co-author Dr. Philip Burnet, Professor from the Department of Psychiatry at the University of Oxford.

For example, genera that were most abundant in the most social monkeys included Faecalibacterium and Prevotella. In contrast, the genus Streptococcus, which in humans can cause diseases such as strep and pneumonia, was more abundant in less social monkeys.

“It is particularly striking that we find a strong positive relationship between the abundance of the gut microbe Faecalibacterium and how social the animals are. Faecalibacterium is known for its strong anti-inflammatory properties and is associated with good health,” said Johnson.

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Cause and effect;

But what drives the relationship between social connectedness and gut microbiome composition? The distinction between cause and effect is not easy.

“The relationship between social behavior and microbial abundance may be the direct result of social transmission of microbes, for example through grooming. It could also be an indirect effect, as monkeys with fewer friends may be more stressed, which then affects the abundance of them.In addition to the microbiome influencing behavior, we also know that it is a reciprocal relationship, where the microbiome can with the in turn to affect the brain and behavior,” Johnson said.

Co-author Dr. Robin Dunbar, Professor from the Department of Experimental Psychology at the University of Oxford, said: “As our society increasingly replaces online interactions with real-world ones, these important research findings highlight the fact that as primates we evolved not only in a social world , but also to a microbial”.