Social behavior and the gut microbiome in wild baboons

Background/Question/Methods Vertebrate intestines are home to thousands of bacterial species that exert profound effects on their hosts. However, large gaps remain in our understanding of the forces that shape gut microbiome composition. Among the least understood but potentially most significant such forces are the effects of host social interactions. From an evolutionary perspective, social effects on the gut microbiome may be an underappreciated consequence of group living, associated with both fitness costs and benefits. Working in the intensively studied Amboseli baboons of Kenya, we used long-term behavioral data and shotgun metagenomic sequencing to test whether social group structure and social interactions within groups predict either the taxonomic or the functional composition of the gut microbiome.

Results/Conclusions We found that social group membership and social network relationships predicted both the taxonomic structure of the gut microbiome and the structure of genes encoded by gut microbial species. Rates of interaction directly explained variation in the gut microbiome, even after controlling for diet, kinship, and shared environments. They therefore strongly implicate direct physical contact among social partners in the transmission of gut microbial species. We identified 51 socially structured taxa, which were significantly enriched for anaerobic and non-spore-forming lifestyles. Our results argue that social interactions are an important determinant of gut microbiome composition in natural animal populations—a relationship with important ramifications for understanding how social relationships influence health, as well as the evolution of group living.