Comparative study of the gut microbiota in three captive Rhinopithecus species
Authors: Xi Li , Wen Xiaohui , Jia Ting , Han Jincheng , Qin Xinxi , Zhang Yanzhen , Wang Zihan 
Published: July 2023

Abstract
Background
Snub-nosed monkeys are highly endangered primates and their population continues to decline with the habitat fragmentation. Artificial feeding and breeding is an important auxiliary conservation strategy. Studies have shown that changes and imbalances in the gut microbiota often cause gastrointestinal problems in captive snub-nosed monkeys. Here, we compare the gut microbiota composition, diversity, and predicted metabolic function of three endangered species of snub-nosed monkeys (Rhinopithecus bieti, R. brelichi, and R. roxellana) under the same captive conditions to further our understanding of the microbiota of these endangered primates and inform captive conservation strategies. 16 S rRNA gene sequencing was performed on fecal samples from 15 individuals (R. bieti N = 5, R. brelichi N = 5, R. roxellana N = 5).

Results
The results showed that the three Rhinopithecus species shared 24.70% of their amplicon sequence variants (ASVs), indicating that the composition of the gut microbiota varied among the three Rhinopithecus species. The phyla Firmicutes and Bacteroidetes represented 69.74% and 18.45% of the core microbiota. In particular, analysis of microbiota diversity and predicted metabolic function revealed a profound impact of host species on the gut microbiota. At the genus level, significant enrichment of cellulolytic genera including Rikenellaceae RC9 gut group, Ruminococcus, Christensenellaceae R7 group, UCG 004 from Erysipelatoclostridiaceae, and UCG 002 and UCG 005 from Oscillospiraceae, and carbohydrate metabolism including propionate and butyrate metabolic pathways in the gut of R. bieti indicated that R. bieti potentially has a stronger ability to use plant fibers as energy substances. Bacteroides, unclassified Muribaculaceae, Treponema, and unclassified Eubacterium coprostanoligenes group were significantly enriched in R. brelichi. Prevotella 9, unclassified Lachnospiraceae, and unclassified UCG 010 from Oscillospirales UCG 010 were significantly enriched in R. roxellana. Among the predicted secondary metabolic pathways, the glycan biosynthesis and metabolism had significantly higher relative abundance in the gut of R. brelichi and R. roxellana than in the gut of R. bieti. The above results suggest that different Rhinopithecus species may have different strategies for carbohydrate metabolism. The Principal coordinate analysis (PCoA) and Unweighted pair-group method with arithmetic mean (UPGMA) clustering tree revealed fewer differences between the gut microbiota of R. brelichi and R. roxellana. Correspondingly, no differences were detected in the relative abundances of functional genes between the two Rhinopithecus species.

Conclusion
Taken together, the study highlights that host species have an effect on the composition and function of the gut microbiota of snub-nosed monkeys. Therefore, the host species should be considered when developing nutritional strategies and investigating the effects of niche on the gut microbiota of snub-nosed monkeys.