Digestive Adaptations of Both the Fore- and Hind-gut in a Temperate Colobine Monkey

Background: In mammal herbivores, the digestion of fiber usually occurs predominantly in either the foregut or in the hindgut. However, how both gut regions function synergistically in the digestion of fiber and other nutrients has rarely been reported in wild mammals. This requires an integrative study of host anatomy, physiology and gut microbiome. Colobine monkeys (Colobinae) are folivorous, with fiber fermentation primarily occurring in the foregut, with residual fermentation in the hindgut. For the few colobine species that live in temperate regions obtaining energy from fiber during winter is critical but the mechanisms enabling this remain unclear. Results: We studied microbial and morphological digestive adaptations of golden snub-nosed monkeys (GSMs), Rhinopithecus roxellana, a temperate forest colobine from central China. We tested for synergistic foregut and hindgut fiber digestion in a species that experiences high thermal energy demands while restricted to a fibrous, low-energy winter diet. We found that the GSM’s colon has a significantly greater volume than that of other foregut fermenting colobines, and both gut regions of GSMs are dominated by microbial taxa producing enzymes to enable active digestion of complex carbohydrates. The microbiomes of the fore- and hindgut differed significantly in composition and abundance. Although the expression of microbial gene functions for fiber digestion were higher in the foregut than in the hindgut, our microbiome analysis in conjunction with that for morphology, enzyme activity and fiber-protein digestion, suggests complementary fiber and protein metabolism in both gut regions. Conclusions: Our results support that both the GSM fore- and hindgut facilitate fiber digestion, with an enlarged colon consistent as an adaptation to accommodate high throughput of fiber-rich food during winter.