Population genetic analysis of autophagy and phagocytosis genes in <i>Drosophila melanogaster</i> and <i>D</i>. <i>simulans</i>

Autophagy and phagocytosis are cellular immune mechanisms for internalization and elimination of intracellular and extracellular pathogens. Some pathogens have evolved the ability to inhibit or manipulate these processes, raising the prospect of adaptive reciprocal co-evolution by the host. We performed population genetic analyses on phagocytosis and autophagy genes in Drosophila melanogaster and D. simulans to test for molecular evolutionary signatures of immune adaptation. We found that phagocytosis and autophagy genes as a whole exhibited an elevated level of haplotype homozygosity in both species. In addition, we detected signatures of recent selection, notably in the Atg14 and Ykt6 genes in D. melanogaster and a pattern of elevated sequence divergence in the genderblind (gb) gene on the D. simulans lineage. These results suggest that the evolution of the host cellular immune system as a whole may be shaped by a dynamic conflict between Drosophila and its pathogens even without pervasive evidence of strong adaptive evolution at the individual gene level.细胞自噬（autophagy）与吞噬作用（phagocytosis）是介导胞内与胞外病原体内化并清除的细胞免疫机制。部分病原体已演化出抑制或操纵这些过程的能力，这提示宿主可产生适应性双向共演化的响应。本研究对黑腹果蝇（Drosophila melanogaster）与拟果蝇（Drosophila simulans）的吞噬作用与细胞自噬相关基因开展群体遗传分析，以检验免疫适应性的分子演化特征。研究发现，在两个果蝇物种中，吞噬作用与细胞自噬相关基因整体的单倍型纯合度均有所升高。此外，本研究还检测到近期选择的分子特征：在黑腹果蝇中尤其体现在Atg14与Ykt6基因，而在拟果蝇谱系中，盲性别基因（genderblind，gb）呈现序列分化水平升高的模式。上述结果表明，即便在单个基因层面缺乏强适应性演化的广泛证据，果蝇与其病原体之间的动态互作冲突仍可能整体塑造宿主细胞免疫系统的演化历程。