The adaptation of the gut microbiome to social environmental changes in an Asian langur

Social environments profoundly impact social animals' gut microbiome. Understanding such effects is critical for evaluating population fitness and conservation. Employing 16S rRNA and metagenomic sequencing, we investigated the gut microbiome of the endangered white-headed langur ( Trachypithecus leucocephalus ) to clarify its potential adaptive strategies to social environmental changes. Distinct differences were observed among social groups: the all-male group was enriched in Bacillota and showed stronger cellulose degradation potential, which might be associated with greater cellulose intake and higher cortisol and T3 levels; mixed-sex group was enriched in Actinomycetota, Pseudomonadota, and non-carbohydrate metabolism genes, possibly due to more young leaves consumption and reproductive needs. Alpha male replacement also shaped gut microbiome: the third alpha male period had highest Bacteroidota and lowest metabolic genes abundance, potentially related to improved food quality during this period. These preliminary findings highlight gut microbial adaptation to social environments in the studied population, providing implications for the conservation of this endangered species.