Data from: Disentangling the roles of natural selection and genetic drift in shaping variation at MHC immunity genes

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 opposing 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 approximately 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（major histocompatibility complex，MHC）是脊椎动物免疫应答的核心组成部分，且因受到强烈的选择压力，成为整个基因组中多态性最为丰富的区域之一。尽管已有超过15年的研究积累，针对种群瓶颈过程中作用于MHC基因的两股对立进化驱动力——选择与遗传漂变的相对作用，实证研究却给出了极具分歧的解释。本研究采用元分析方法，对探讨种群瓶颈对MHC多态性影响的相关研究结果进行量化整合。研究表明，种群瓶颈事件发生前作用于MHC基因座的选择效应，与瓶颈过程中的遗传漂变共同作用，将导致MHC多态性的整体丢失量较中性遗传多样性的丢失量高出约15%。该结果与“选择应维持MHC多态性”的普遍预期相悖，但却与近期模拟模型以及至少两项实证研究的结果相符。值得注意的是，本研究结果表明，在瓶颈前种群中维持高水平MHC多态性的过程中，负频率依赖选择或许比超显性发挥更为关键的作用。