Data from: Maintaining functional major histocompatibility complex diversity under inbreeding: the case of a selfing vertebrate

Major histocompatibility complex (MHC) genes encode proteins that present pathogen-derived antigens to T-cells, initiating the adaptive immune response in vertebrates. Although populations with low MHC diversity tend to be more susceptible to pathogens, some bottlenecked populations persist and even increase in numbers despite low MHC diversity. Thus, the relative importance of MHC diversity versus genome-wide variability for the long-term viability of populations after bottlenecks and/or under high inbreeding is controversial. We tested the hypothesis that genome-wide inbreeding (estimated using microsatellites) should be more critical than MHC diversity alone in determining pathogen resistance in the self-fertilising fish Kryptolebias marmoratus by analysing MHC diversity and parasite loads in natural and laboratory populations with different degrees of inbreeding. Both MHC and neutral diversities were lost after several generations of selfing, but we also found evidence of parasite selection acting on MHC diversity and of non-random loss of alleles, suggesting a possible selective advantage of those individuals with functionally divergent MHC, in accordance to the hypothesis of divergent allele advantage. Moreover, we found that parasite loads were better explained by including MHC diversity in the model than by genome-wide (microsatellites) heterozygosity alone. Our results suggest that immune-related overdominance could be key in maintaining variables rates of selfing and outcrossing in K. marmoratus and other mixed-mating species.

主要组织相容性复合体（Major histocompatibility complex，MHC）编码能将病原体衍生抗原呈递给T细胞的蛋白质，从而启动脊椎动物的适应性免疫应答。尽管MHC多样性较低的种群往往对病原体更易感，但部分经历过种群瓶颈的种群即便MHC多样性低下，仍能存续甚至种群数量增长。因此，在种群瓶颈事件后或高近交状态下，MHC多样性与全基因组变异对种群长期存续的相对重要性仍存在争议。本研究以自交鱼类斑纹隐小鳉（Kryptolebias marmoratus）为研究对象，通过分析不同近交程度的自然种群与实验室种群的MHC多样性及寄生虫载荷量，检验了“全基因组近交（通过微卫星（microsatellites）估算）相较于单独的MHC多样性，对决定种群的病原体抗性更为关键”这一假说。经过多代自交后，MHC多样性与中性多样性均出现丢失，但本研究同时发现寄生虫选择作用于MHC多样性以及等位基因非随机丢失的证据，提示具有功能异型MHC的个体可能存在选择优势，这与异型等位基因优势假说相符。此外，本研究发现，相较于仅使用全基因组（微卫星）杂合度，在模型中纳入MHC多样性能更好地解释寄生虫载荷量。本研究结果表明，与免疫相关的超显性或许是维持斑纹隐小鳉（Kryptolebias marmoratus）及其他混合交配物种自交与异交速率差异的关键因素。