Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
Mol Ecol. 2011 Nov;20(21):4408-20. doi: 10.1111/j.1365-294X.2011.05292.x. Epub 2011 Oct 10.
The major histocompatibility complex (MHC) forms an integral component of the vertebrate immune response and, due to strong selection pressures, is one of the most polymorphic regions of the entire genome. Despite over 15 years of research, empirical studies offer highly contradictory explanations of the relative roles of different evolutionary forces, selection and genetic drift, acting on MHC genes during population bottlenecks. Here, we take a meta-analytical approach to quantify the results of studies into the effects of bottlenecks on MHC polymorphism. We show that the consequences of selection acting on MHC loci prior to a bottleneck event, combined with drift during the bottleneck, will result in overall loss of MHC polymorphism that is ∼15% greater than loss of neutral genetic diversity. These results are counter to general expectations that selection should maintain MHC polymorphism, but do agree with the results of recent simulation models and at least two empirical studies. Notably, our results suggest that negative frequency-dependent selection could be more important than overdominance for maintaining high MHC polymorphism in pre-bottlenecked populations.
主要组织相容性复合体（MHC）是脊椎动物免疫反应的一个组成部分，由于受到强烈的选择压力，它是整个基因组中多态性最强的区域之一。尽管已经进行了超过 15 年的研究，但实证研究对不同进化力量（选择和遗传漂变）在种群瓶颈期对 MHC 基因的相对作用提供了高度矛盾的解释。在这里，我们采用元分析的方法来量化研究瓶颈对 MHC 多态性影响的结果。我们表明，在瓶颈事件之前作用于 MHC 基因座的选择的后果，加上瓶颈期间的漂变，将导致 MHC 多态性的总体丧失，比中性遗传多样性的丧失高出约 15%。这些结果与选择应该维持 MHC 多态性的一般预期相悖，但与最近的模拟模型和至少两项实证研究的结果一致。值得注意的是，我们的结果表明，在瓶颈前的种群中，负频率依赖性选择可能比超显性对维持高 MHC 多态性更为重要。
