Scientists have shown for the first time that monkeys that are more sociable have a healthier gut microbiome. For example, they have more of the beneficial bacteria Faecalibacterium and Prevotella, and fewer of the typically pathogenic bacteria such as some members of the genus Streptococcus.
This is further evidence that in primates, social connectedness translates into good physical and mental health, and vice versa.
There is 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 can be transmitted socially, for example through touch. Studying other primates provides an opportunity to learn more about ourselves.
The new findings relate to rhesus macaques, Macaca mulatta. The rhesus macaque is diurnal, arboreal, and terrestrial. It is mostly herbivorous, feeding mainly on fruit, but also eating seeds, roots, buds, bark, and cereals, and consumes around 99 different plant species.
Lead author Dr Katerina Johnson, a research associate at the Department of Experimental Psychology and the Department of Psychiatry of the University of Oxford, says: “Here we show that more sociable monkeys have a higher abundance of beneficial gut bacteria, and a lower abundance of potentially disease-causing bacteria.”
For the research, 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. The monkeys range and forage freely, although their diet gets supplemented daily with monkey chow.
Between 2012 and 2013, a total of 50 uncontaminated stool samples were collected from this social group. As a measure of social connectedness, the authors used the time each monkey spent grooming or being groomed, and his or her number of grooming partners.
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.
The researchers assessed DNA sequence data from the stool samples to measure the composition and diversity of the gut microbial community, and looked at the relationship with social connectivity.
They also took into account sex, age, season, and rank within the group’s hierarchy. They focused on microbes that have been repeatedly shown to be either more or less abundant in people or rodents with autism-like symptoms (commonly accompanied by social disconnection) or which are socially isolated.
The researchers found that engagement in social interactions were 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.
While there is a pattern, what drives the relationship between social connectedness and gut microbiome composition is not clear. Distinguishing between cause and effect is not easy and further research is required.
The research has been published in the journal Frontiers in Microbiology. The study is titled “Sociability in a non-captive macaque population is associated with beneficial gut bacteria.”
