Interactions between social groups of colobus monkeys (Colobus vellerosus) explain similarities in their gut microbiomes

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 in wild populations. We investigated whether diet, relatedness or the 1m proximity network best explains differences in the gut microbiome among 45 female colobus monkeys in eight social groups residing at Boabeng-Fiema, Ghana. We combined demographic and behavioural data collected during May – August 2007 and October 2008 – April 2009 with 16S rRNA sequencing of faecal samples collected during the latter part of each observation period. Depending on the beta diversity index, social group identity explained 19–28% of the variation in gut microbiome beta diversity. When comparing the predictive power of dietary dissimilarity, relatedness and connectedness in the 1m proximity network, the models with social connectedness received the strongest support, even in our analyses that excluded within-group dyads. This novel finding indicates that microbes may be transmitted during intergroup encounters, which could occur either indirectly via shared environments or directly via social contact. Lastly, some of the gut microbial taxa that appear to be transmitted via 1m proximity are associated with digestion of plant material. Further research is needed to investigate whether this type of gut microbe transmission yields health benefits, which could provide an incentive for the formation and maintenance of social bonds within and between social groups. •Colobus group ID and home range separation predicted gut microbiome differences.•Between-group differences in the gut microbiome decreased with social connectedness.•This social network metric was a better predictor than diet and relatedness.•Microbes transmitted during between-group encounters may help the host digest leaves.