Data from: Patterns of selection and allele diversity of class I and class II major histocompatibility loci across the species range of sockeye salmon (Oncorhynchus nerka)

The major histocompatibility complex (MHC), an important component of the vertebrate immune system, provides an important suite of genes to examine the role of genetic diversity at non-neutral loci for population persistence. We contrasted patterns of diversity at the two classical MHC loci in sockeye salmon (Oncorhynchus nerka), MHC class I (UBA) and MHC class II (DAB), and neutral microsatellite loci across 70 populations spanning the species range from Washington State to Japan. There was no correlation in allelic richness or heterozygosity between MHC loci or between MHC loci and microsatellites. The two unlinked MHC loci may be responding to different selective pressures; the distribution of FST values for the two loci was uncorrelated, and evidence for both balancing and directional selection on alleles and lineages of DAB and UBA was observed in populations throughout the species range but rarely on both loci within a population. These results suggest that fluctuating selection has resulted in the divergence of MHC loci in contemporary populations.主要组织相容性复合体（major histocompatibility complex, MHC）是脊椎动物免疫系统的重要组成部分，其包含的一系列基因为探究非中性位点的遗传多样性对种群存续的意义提供了关键研究载体。本研究针对红大马哈鱼（Oncorhynchus nerka）的两个经典MHC位点——MHC I类（UBA）与MHC II类（DAB）——以及中性微卫星位点的多样性模式展开对比分析，样本覆盖了该物种从华盛顿州至日本的整个分布范围，共纳入70个种群。研究发现，MHC位点之间，以及MHC位点与微卫星位点之间，均未在等位基因丰富度或杂合度上呈现显著相关性。两个非连锁的MHC位点可能受到不同选择压力的调控：二者的FST值分布不存在相关性，且在覆盖物种全分布范围的种群中，均观测到DAB与UBA的等位基因及谱系受到平衡选择与定向选择作用的证据，但在单个种群内同时在两个位点上发现此类证据的情况极少。上述结果表明，波动选择驱动了当代种群中MHC位点的分化。