Highly specialized plant-based diets drive the decrease of gut microbiota diversity and lignocellulose-degrading function

Dietary specialization represents an extreme adaptive strategy in mammals, yet its effects on the gut microbiome remain poorly understood. Here, we investigated the gut microbiomes of three wild bamboo dietary specialists—the Chinese bamboo rat, giant panda, and Chinese red panda—together with their respective relatives, and extended to additional leaf dietary specialists, including folivorous colobines, folivorous lemurs, and koalas. By integrating 16S rRNA and metagenome data with lignocellulose‑degrading enzyme assay experiments, we revealed an unconventional pattern across feeding guilds: highly specialized plant‑based diets drive the decrease of gut microbiota diversity and carbohydrate metabolic capacity. Despite shared bamboo diets, bamboo rats showed no gut microbiome convergence with pandas, underscoring gut morphology as a key constraint. Across dietary specialists, polysaccharide metabolism, lignocellulose‑degrading gene repertoires, and associated enzyme activities diminished, while pathways for plant secondary metabolite detoxification were enriched. These results emphasize the role of host–microbe compensatory strategies rather than enhanced carbohydrate metabolism in extreme plant dietary adaptation, and call for more natural dietary variability in the captive management of endangered specialists.