Social interactions across groups of colobus monkeys ( Colobus vellerosus ) explain similarities in their gut microbiomes

Abstract The gut microbiome is structured by social groups in a variety of host taxa. Whether this pattern is driven by relatedness, similar diets, or shared social environments is under debate because few studies have had access to the data necessary to disentangle these factors. We investigated whether diet, relatedness, or 1-meter proximity networks best explains differences in the gut microbiome among 45 female colobus monkeys in 8 groups residing at Boabeng-Fiema, Ghana. We combined demographic and behavioural data collected May – August 2007 and October 2008 – April 2009 with 16S rRNA sequencing of faecal samples collected during the latter part of each observation period. Group identity explained a large percentage of the variation in gut microbiome beta-diversity. When comparing the predictive power of dietary dissimilarity, relatedness, and distance in the 1-meter proximity network, the models with social distance received the strongest support. Thus, social proximity plays a larger role than diet and relatedness in generating group-level gut microbiome signatures, corroborating previous findings of the importance of social transmission of gut microbes within groups. Our novel findings also show how a social network metric predicts gut microbiome similarity of non-group members, indicating that microbes may be transmitted during intergroup encounters. Lastly, some of the socially transmitted gut microbial taxa are associated with digestion of plant material, but further research is needed to investigate whether social transmission of gut microbes yields health benefits, which could provide an incentive for the formation and maintenance of social bonds within and between groups.