New research, published today in the ISME Journal, has found that the gut microbiomes of mice are significantly impacted by the social networks they form.
Wild animals vary massively in their microbiomes – a term referring to the community of trillions of microorganisms that live inside the bodies of mammals including humans. Gut-dwelling microbes play particularly important roles in mammal biology, enhancing digestion, regulating our immune systems, and fending off harmful bacteria. The specific cocktail of microbes we host is a hugely influential part of our body, yet unlike our own cells these bacteria are readily exchanged with the outside world, making contact with others and the environment an important force shaping the microbiome.
Previous studies in primates have suggested that social contacts can provide important conduits through which hosts exchange gut microbes with one another. However, to what extent social acquisition of microbiomes is important across animal species, or whether it also applies to less social species that do not live in tight-knit groups, is not well understood.
To learn more about the effect of social interactions on the microbiome, Oxford PhD student Aura Raulo and colleagues studied a population of wild mice in the UK, microchipping them to track their movement and behaviour.
By analysing this data, together with faecal samples, the researchers could assess how a mouse’s environment and social life might be affecting which bacteria end up in its gut.
Their results were striking. Although these mice do not live in stable groups, social relationships among mice influenced their microbiome composition more than ten times as strongly as any other factor studied (including effects of shared space use and kinship). Mice that were occasionally observed together typically shared around 30% of their gut microbes, whereas this rose to 60% for mice that were regularly observed together. This social effect was sufficiently strong that mice observed together just once shared more bacteria than those that were never observed together.
Interestingly, sex was important in these trends, with social contacts involving males having a much greater influence on the microbiome than those involving only females. The team also found that the most diverse microbiomes were found from mice who were well-connected in the social network or bridged distinct social ‘circles’.
The researchers point out that the suggested links between social contact and a healthy gut microbiome could have implications for humans – particularly as the acquisition of microbes from the environment, including the social environment, plays an important role in the development of children’s immune systems.
Lead researcher Aura Raulo said: ‘The guts of mammals are teeming with beneficial microbes, yet how we acquire them remains poorly understood. At the same time, we have a long tradition of epidemiology in studying how disease-causing pathogens travel from one host to another through networks of social contacts. Our new study with wild mice suggests that social contact can provide a key pathway for the transmission of gut microbes, strongly shaping and enriching the adult gut microbiome, even in a relatively unsocial species.
‘This raises questions about the very basic assumption of social contact always being an epidemiological risk, never an opportunity. While the benefits of avoiding social contact to hinder spread of infectious disease are now more obvious than ever, by isolating ourselves from disease, are we isolating ourselves from the flux of beneficial symbionts as well? Can lack of social contact lead to unforeseen health consequences through compromising the diversity and resilience of our gut microbiomes?’
The team plans to build on these results by trying to identify which types of bacteria are most likely to be transmitted socially, and to what extent animal behaviour in turn is influenced by the microbiome. Uncovering how animal behaviour and the gut microbiome affect each other could shed light on the kind of roles these microbes may have played in the very evolution of social behaviour. What we can now say is that social contact between animals likely represents much more than just an epidemiological risk.