# Moderate Genetic Diversity of MHC Genes in an Isolated Small Population of Black-and-White Snub-Nosed Monkeys (Rhinopithecus bieti)

## TL;DR

This study examines genetic diversity in an isolated population of black-and-white snub-nosed monkeys, finding moderate diversity in MHC genes linked to immune function.

## Contribution

The study integrates adaptive MHC genes and neutral markers to assess genetic diversity in an endangered primate species.

## Key findings

- Neutral microsatellites show high heterozygosity and polymorphism.
- MHC genes display high heterozygosity but moderate polymorphism.
- Balancing selection and trans-species evolution influence MHC diversity.

## Abstract

Genetic diversity plays a crucial role in determining the ability of populations to evolve. We investigated the genetic variation of the black-and-white snub-nosed monkey by integrating adaptive MHC genes and neutral microsatellites. We found that neutral loci exhibited high heterozygosity and a high degree of polymorphism, while MHC genes showed high heterozygosity and moderate polymorphism. Additionally, positive selection and trans-species evolution indicated that historical balancing selection might have sustained the MHC polymorphism. This study provides valuable scientific evidence and a reference for formulating or amending conservation strategies for black-and-white snub-nosed monkeys.

Genetic diversity is an essential indicator that echoes the natural selection and environmental adaptation of a species. Isolated small populations are vulnerable to genetic drift, inbreeding, and limited gene flow; thus, assessing their genetic diversity is critical in conservation. In this study, we studied the genetic diversity of black-and-white snub-nosed monkeys (Rhinopithecus bieti) using neutral microsatellites and five adaptive major histocompatibility complex (MHC) genes. Two DQA1 alleles, two DQB1 alleles, two DRB1 alleles, two DRB5 alleles, and three DPB1 alleles were isolated from a population. The results indicate that neutral microsatellites demonstrate a high degree of heterozygosity and polymorphism, while adaptive MHC genes display a high degree of heterozygosity and moderate polymorphism. The results also show that balancing selection has prominently influenced the MHC diversity of the species during evolution: (1) significant positive selection is identified at several amino acid sites (primarily at and near antigen-binding sites) of the DRB1, DRB5, and DQB1 genes; (2) phylogenetic analyses display the patterns of trans-species evolution for all MHC loci. This study provides valuable genetic diversity insights into black-and-white snub-nosed monkeys, which dwell at the highest altitude and have experienced the harshest environmental selection of all primates globally since the Pleistocene. Such results provide valuable scientific evidence and a reference for making or amending conservation strategies for this endangered primate species.