Social connections are essential for good health and wellbeing in social animals, equivalent to ourselves and other primates. There may be also increasing 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 might be transmitted socially, for instance through touch. So how does social connectedness translate into the composition and variety of the gut microbiome? That is the topic of a latest study in Frontiers in Microbiology on rhesus macaques, Macaca mulatta.

Here we show that more sociable monkeys have a better abundance of useful gut bacteria, and a lower abundance of doubtless disease-causing bacteria.”

Dr Katerina Johnson, lead writer, research associate, Department of Experimental Psychology and the Department of Psychiatry, University of Oxford

Monkey island

The scientists focused on a single social group (with 22 males and 16 females between the ages of six and 20 years) of rhesus macaques on the island of Cayo Santiago, off the eastern coast of Puerto Rico. Macaques originally only lived in North Africa and Asia. But in 1938, a founder population of 409 rhesus macaques was moved from India to Cayo Santiago. Today, greater than 1,000 macaques live to tell the tale the 15.2 hectare island, divided into several social groups. They vary and forage freely, although their weight-reduction plan gets supplemented day by day with monkey chow. Researchers do behavioral observations on the monkeys annually.

Between 2012 and 2013, the authors collected a complete of fifty 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 his or her variety of grooming partners.

Social grooming

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

Johnson, Watson et al. analyzed DNA sequence data from the stool samples to measure the composition and variety of the gut microbial community, and checked out the connection with social connectivity. In addition they took under consideration sex, age, season, and rank inside the group’s hierarchy. They focused on microbes which have been repeatedly shown in to be either roughly abundant in people or rodents with autism-like symptoms (commonly accompanied by social disconnection) or that are socially deprived.

Sociable monkeys have more ‘good’ microbes

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

For instance, genera more abundant in probably the most sociable monkeys included Faecalibacterium and Prevotella. Conversely, the genus Streptococcus, which in humans may cause diseases equivalent to strep throat and, pneumonia, was most abundant in less sociable monkeys.

“It is especially striking that we discover a powerful positive relationship between the abundance of the gut microbe Faecalibacterium and the way sociable the animals are. Faecalibacterium is well-known for its potent anti-inflammatory properties and is related to good health,” said Johnson.

Cause and effect?

But what drives the connection between social connectedness and gut microbiome composition? Distinguishing between cause and effect is not easy.

“The connection between social behavior and microbial abundances would be the direct results of social transmission of microbes, for instance through grooming. It is also an indirect effect, as monkeys with fewer friends could also be more stressed, which then affects the abundance of those microbes. In addition to behavior influencing the microbiome, we also understand it is a reciprocal relationship, whereby the microbiome can in turn affect the brain and behavior,” said Johnson.

Co-author Dr Robin Dunbar, a professor from the Department of Experimental Psychology on the University of Oxford, said: “As our society is increasingly substituting online interactions for real-life ones, these essential research findings underline the incontrovertible fact that as primates, we evolved not only in a social world but a microbial one as well.”

Source:

Journal reference:

Johnson, K., et al. (2022) Sociability in a non-captive macaque population is related to useful gut bacteria. Frontiers in Microbiology. doi.org/10.3389/fmicb.2022.1032495.