Table_2_Genetic Diversity and Differentiation of MHC Class I Genes in Red-Crowned Crane Populations.XLSX

The red-crowned crane (Grus japonensis) has been demoted to “vulnerable species” because its populations have apparently stabilized in Japan and Korea. Low variation and genetic drift may cause damage to the nascent recovery of the G. japonensis population. The major histocompatibility complex (MHC) is one of the most polymorphic gene families in the vertebrate genome and can reflect information on the adaptive evolution of endangered species. In this study, variations in MHC I exon 3 of captive G. japonensis in China were assessed and compared with those in cranes from Japan. Forty MHC alleles of 274 base pairs were isolated from 32 individuals from two captive populations in China. There was high variability in the nucleotide and amino acid composition, showing the proportion of polymorphic sites of 18.98 and 32.97%, respectively. Comparative analyses of the Chinese and Japanese populations based on 222 base pair sequences revealed more alleles and higher variation in the Chinese population. The lack of significant geographical differentiation of G. japonensis was supported by the genetic differentiation coefficient (0.04506) between the Chinese and Japanese populations. Positive selection of antigen-binding sites was observed, which contributed to maintaining the diversity of MHC class I genes. Phylogenetic analysis suggested the persistence of trans-species polymorphisms among MHC class I genes in Gruidae species. Our results may contribute to optimizing the management of G. japonensis populations and population recovery of this threatened species.

丹顶鹤（Grus japonensis）因日本与韩国的种群数量趋于稳定，已被降级为易危物种（vulnerable species）。遗传变异匮乏与遗传漂变或会损害丹顶鹤种群的初步恢复进程。主要组织相容性复合体（major histocompatibility complex, MHC）是脊椎动物基因组中多态性最高的基因家族之一，可反映濒危物种的适应性进化信息。本研究针对中国圈养丹顶鹤的MHC I类基因外显子3（exon 3）的变异情况展开评估，并与日本鹤类的对应变异进行对比。研究从中国两个圈养种群的32个个体中，成功分离得到长度为274个碱基对的40个MHC等位基因。该序列的核苷酸与氨基酸组成均呈现高度多态性，多态位点占比分别为18.98%与32.97%。基于222个碱基对序列开展的中、日种群比较分析显示，中国种群拥有更多的等位基因，且变异水平更高。中、日种群间的遗传分化系数为0.04506，这一结果支持丹顶鹤不存在显著地理分化的结论。本研究观察到抗原结合位点受到正向选择作用，该作用对维持MHC I类基因的多样性具有关键意义。系统发育分析表明，鹤科（Gruidae）物种的MHC I类基因间持续存在跨物种多态性。本研究结果可为优化丹顶鹤种群管理及该濒危物种的种群恢复工作提供理论支撑。