Social Behaviour Drives Gut Microbiome Community Assembly Among Wild Long‐Tailed Macaques ( Macaca fascicularis ) in Thailand

The ‘social microbiome’ conceptualises gut microbial communities as ‘islands’ of host social organisation. Yet, in comparison to broader aspects of social organisation such as animals' group membership and composition, the impact of inter‐individual differences in sociality on microbiome community ecology remains less well studied. Among a wild but human‐provisioned group of long‐tailed macaques ( Macaca fascicularis ), we assessed the relative effects of individuals' sociality, compared to their demographic characteristics, anthropogenic and abiotic environmental factors, and microbe‐microbe associations, on the relative abundance and co‐occurrence of bacterial taxa. Bipartite network analysis showed that bacterial communities among macaques were nested rather than segregated or modular structures. Several ‘core’ bacterial genera were found across all macaques, but other ‘non‐core’ bacteria were found only in a few macaques suggesting that their occurrence/abundance may be influenced by transient environmental factors. Joint Species Distributions Models showed that macaques' sociality, particularly their dominance rank and their connectedness or centrality within their social grooming network, had the strongest impact on taxa abundance, followed by their demographic characteristics, and finally their exposure to both anthropogenic and abiotic environmental factors. Phylogenetically distant taxa were more likely to co‐occur within the same macaque hosts than phylogenetically related taxa. These findings confirm that microbiome communities are strongly influenced by the social status and connectedness of individual hosts. Nevertheless, the finding that some taxa were more prevalent among high‐ranking or well‐connected macaques, while others were more prevalent among low‐ranking or socially peripheral macaques, warrants further investigation into how individual differences in social microbiomes might affect their health and fitness. Future studies, through the collection of behavioural and microbial data on additional macaque groups, may provide further insights into the relative effects of animals' social organisation and social behaviours on microbiomes.