Evolution of the MHC-DQB exon 2 in marine and terrestrial mammals

On the basis of a general low polymorphism, several studies suggest that balancing selection in the class II major histocompatibility complex (MHC) is weaker in marine mammals as compared with terrestrial mammals. We investigated such differential selection among Cetacea, Artiodactyla, and Primates at exon 2 of MHC-DQB gene by contrasting indicators of molecular evolution such as occurrence of transpecific polymorphisms, patterns of phylogenetic branch lengths by codon position, rates of nonsynonymous and synonymous substitutions as well as accumulation of variable sites on the sampling of alleles. These indicators were compared between the DQB and the mitochondrial cytochrome b gene (cytb) as a reference of neutral expectations and differences between molecular clocks resulting from life history and historical demography. All indicators showed that the influence of balancing selection on the DQB is more variable and overall weaker for cetaceans. In our sampling, ziphiids, the sperm wha...

基于普遍较低的多态性水平，多项研究表明，与陆生哺乳动物相比，海洋哺乳动物的II类主要组织相容性复合体（major histocompatibility complex, MHC）所受的平衡选择强度更弱。本研究针对鲸目（Cetacea）、偶蹄目（Artiodactyla）与灵长目（Primates），通过对比分子进化相关指标——包括跨物种多态性的出现情况、密码子位点的系统发育分支长度模式、非同义替换与同义替换速率，以及等位基因样本中变异位点的积累情况——对MHC-DQB基因外显子2（exon 2）上的选择压力差异展开了探究。我们以线粒体细胞色素b基因（cytochrome b gene, cytb）作为中性进化预期的参照，对比了DQB基因与该基因间的演化差异，并结合生活史与历史种群动态所导致的分子钟差异开展了分析。所有指标均显示，平衡选择对DQB基因的影响在鲸类中更为多变，且整体强度更弱。在本次采样范围内，剑吻鲸科（ziphiids）、抹香鲸（sperm wha……