Having good friendships can improve health

image: Rhesus macaques in Cayo Santiago grooming themselves
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Social bonds are essential to the good health and well-being of social animals, like ourselves and other primates. There is also growing evidence that the gut microbiome – through what is known as the “gut-brain axis” – plays a key role in our physical and mental health and that bacteria can be transmitted socially, for example by touch. So how does social connectivity translate into the composition and diversity of the gut microbiome? This is the subject of a new study in Frontiers in microbiology on rhesus macaques, macaca mulatta.

Lead author Dr Katerina Johnson, a research associate in the Department of Experimental Psychology and Department of Psychiatry at the University of Oxford, said: “We show here that more sociable monkeys have a greater abundance of bacteria beneficial gut and a lower abundance of potentially pathogenic bacteria.

monkey island

The scientists focused on a single social group (with 22 males and 16 females ranging in age from 6 to 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 moved from India to Cayo Santiago. Today, more than 1,000 macaques live on the 15.2-hectare island, divided into several social groups. They roam and feed freely, although their diet is supplemented daily with monkey food. Researchers make behavioral observations on 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 its number of grooming partners.

Social grooming

Co-author Dr Karli Watson, from the University of Colorado Boulder’s Institute for Cognitive Science, explained: “Macaques are very social animals and grooming is their primary means of bonding and maintaining relationships. Grooming therefore provides a good indicator of social interactions. ”

Johnson, Watson et al. analyzed DNA sequence data from stool samples to measure gut microbial community composition and diversity, and examined the relationship with social connectivity. They also took into account gender, age, season and rank in the group hierarchy. They focused on microbes that have repeatedly been shown to be more or less abundant in people or rodents with autism-like symptoms (usually accompanied by social disconnection) or who are socially disadvantaged.

Sociable monkeys have more “good” microbes

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

For example, more abundant genera in the most sociable apes included Faecalibacterium and Prevotelle. Conversely, the type Streptococcuswhich in humans can cause diseases such as strep throat and, pneumonia, was more abundant in less sociable monkeys.

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

Cause and effect?

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

“The relationship between social behavior and microbial abundance may be the direct result of the 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 these microbes. In addition to behavior influencing the microbiome, we also know that this is a reciprocal relationship, in which the microbiome can in turn affect the brain and behavior,” Johnson said.

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

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