Data from: Microevolutionary selection dynamics acting on immune genes of the green veined white butterfly, Pieris napi

Insects rely on their innate immune system to successfully mediate complex interactions with their microbiota, as well as the microbes present in the environment. Previous work has shown that components of the canonical immune gene repertoire evolve rapidly and have evolutionary characteristics originating from interactions with fast-evolving microorganisms. Although these interactions are likely to vary among populations, there is a poor understanding of the microevolutionary dynamics of immune genes, especially in non-Dipteran insects. Here we use the full set of canonical insect immune genes to investigate microevolutionary dynamics acting on these genes between and among populations by comparing three allopatric populations of the Green Veined White butterfly, Pieris napi (Lepidoptera, Pieridae). Immune genes showed increased genetic diversity compared to genes from the rest of the genome and various functional categories exhibited different types of signatures of selection, at different evolutionary scales, presenting a complex pattern of selection dynamics. Signatures of balancing selection were identified in 10 genes, and 17 genes appear to be under positive selection. Genes involved with the cellular arm of the immune response as well as the Toll pathway appear to be enriched among our outlier loci, regardless of functional category. This suggests that the targets of selection might focus upon an entire pathway, more than on functional subsets across pathways. Our microevolutionary results are similar to previously observed macroevolutionary patterns from diverse taxa, suggesting that either the immune system is robust to dramatic differences in life history and microbial communities, or that diverse microbes exert similar selection pressures.

昆虫依赖其先天免疫系统 (innate immune system)，成功介导与自身微生物群及环境中微生物的复杂相互作用。既往研究表明，经典免疫基因库 (canonical immune gene repertoire) 的组分进化速率较快，且其进化特征源自与快速进化微生物的相互作用。尽管这类相互作用可能因种群而异，但学界对免疫基因的微进化动态 (microevolutionary dynamics) 仍知之甚少，在非双翅目 (Dipteran) 昆虫中更是如此。
本研究以绿纹白蝶（*Pieris napi*，鳞翅目 Lepidoptera：粉蝶科 Pieridae）的三个异域种群为研究材料，利用全套昆虫经典免疫基因，探究了种群间与种群内部作用于这些基因的微进化动态。结果显示，免疫基因相较于基因组其余基因展现出更高的遗传多样性 (genetic diversity)，且各类功能类别在不同进化尺度下呈现出各异的选择信号 (signatures of selection)，构成了复杂的选择动态格局。
研究在10个基因中鉴定到平衡选择 (balancing selection) 的信号，另有17个基因似乎处于正向选择 (positive selection) 作用之下。无论功能类别如何，参与细胞免疫分支 (cellular arm of the immune response) 以及Toll通路 (Toll pathway) 的基因在本次分析的离群位点 (outlier loci) 中显著富集。这提示选择的靶标可能聚焦于整条通路，而非跨通路的功能子集。
本研究得到的微进化结果与此前在多样类群中观察到的宏观进化格局 (macroevolutionary patterns) 相似，这表明要么免疫系统对生活史与微生物群落的显著差异具备鲁棒性 (robustness)，要么多样的微生物施加了相似的选择压力。