Data from: The potential for adaptive maintenance of diversity in antimicrobial peptides

Genes involved in immune defence are among the fastest evolving in the genomes of many species. Interestingly, however, genes encoding antimicrobial peptides (AMPs) have shown little evidence for adaptive divergence in arthropods, despite the centrality of these peptides in direct killing of microbial pathogens. This observation, coupled with a failure to detect phenotypic consequence of genetic variation in AMPs, has led to the hypothesis that individual AMPs make minor contributions to overall immune defence and that AMPs instead act as a collective cocktail. Recent data, however, have suggested an alternative explanation for the apparent lack of adaptive divergence in AMP genes. Molecular evolutionary and phenotypic data have begun to suggest that variant AMP alleles may be maintained through balancing selection in invertebrates, a pattern similar to that observed in several vertebrate AMPs. Signatures of balancing selection include high rates of non-synonymous polymorphism, trans-species amino acid polymorphisms, and convergence of amino acid states across the phylogeny. In this review, we revisit published literature on insect AMP genes and analyse newly available population genomic datasets in Drosophila, finding enrichment for patterns consistent with adaptive maintenance of polymorphism.

参与免疫防御的基因，是众多物种基因组中进化速率最快的基因类群之一。然而值得注意的是，尽管抗菌肽（antimicrobial peptides, AMPs）在直接杀灭病原微生物过程中发挥核心作用，但节肢动物体内编码这类肽的基因几乎未表现出适应性分化的相关证据。这一现象，加上未能在AMPs中检测到遗传变异对应的表型效应，催生了相关假说：单个AMPs对整体免疫防御的贡献微不足道，这类肽类实则以集体鸡尾酒式的组合发挥功能。但近期研究数据为AMPs基因适应性分化缺失的现象提供了另一种解释。分子进化与表型研究数据已开始表明，无脊椎动物体内的变异AMP等位基因可能通过平衡选择得以保留，这一模式与部分脊椎动物AMPs中观察到的现象一致。平衡选择的分子特征包括：非同义多态性频率较高、跨物种氨基酸多态性，以及系统发育树中氨基酸状态的趋同演化。本综述重新梳理了已发表的昆虫AMPs基因相关研究，并分析了果蝇（Drosophila）中新公开的群体基因组数据集，结果发现存在大量与适应性维持多态性相符的特征模式。