Man is a sociable animal, as are other primates. Healthy social ties help people stay in good health, both emotionally and physically. According to a new study published in ‘Frontiers in Microbiology,’ the gut microbiome, which keeps the human gut in good shape, plays an important role in keeping our bodily systems intact. So, how does social interaction fit into the gut microbe’s complex and diversified nexus? Dr. Katerina Johnson assists us in our investigation.
Johnson is a research associate at the University of Oxford’s Departments of Experimental Psychology and Psychiatry. The researchers concentrated on a single social group of rhesus macaques (22 males and 16 females between the ages of six and twenty years) on the island of Cayo Santiago, off the eastern coast of Puerto Rico. Macaques were once found only in North Africa and Asia. However, in 1938, 409 rhesus macaques were relocated from India to Cayo Santiago.
On the 15.2-hectare island today, over 1,000 macaques are divided into several social groups. They are free to roam and forage, though their diet is supplemented daily with monkey chow. Every year, researchers conduct behavioural studies on the monkeys.
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 his or her number of grooming partners.
Co-author Dr Karli Watson, from the Institute of Cognitive Science at the University of Colorado Boulder, explained: “Macaques are highly social animals and grooming is their main way of making and maintaining relationships, so grooming provides a good indicator of social interactions.”
“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, a professor from the Department of Psychiatry at the University of Oxford.
For example, genera more abundant in the most sociable monkeys included Faecalibacterium and Prevotella. Conversely, the genus Streptococcus, which in humans can cause diseases such as strep throat and, pneumonia, was most abundant in less sociable monkeys.
“It is particularly striking that we find a strong positive relationship between the abundance of the gut microbe Faecalibacterium and how sociable the animals are. Faecalibacterium is well known for its potent anti-inflammatory properties and is associated with good health,” said Johnson.
But what drives the relationship between social connectedness and gut microbiome composition? Distinguishing between cause and effect isn’t easy.
“The relationship between social behavior and microbial abundances 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 these microbes. As well as behavior influencing the microbiome, we also know it is a reciprocal relationship, whereby the microbiome can in turn affect the brain and behavior,” said Johnson.