McGonigle John E, Leitão Alexandre B, Ommeslag Sarah, Smith Sophie, Day Jonathan P, Jiggins Francis M
Department of Genetics, University of Cambridge, Cambridge, United Kingdom.
PLoS Pathog. 2017 Oct 19;13(10):e1006683. doi: 10.1371/journal.ppat.1006683. eCollection 2017 Oct.
A priority for biomedical research is to understand the causes of variation in susceptibility to infection. To investigate genetic variation in a model system, we used flies collected from single populations of three different species of Drosophila and artificially selected them for resistance to the parasitoid wasp Leptopilina boulardi, and found that survival rates increased 3 to 30 fold within 6 generations. Resistance in all three species involves a large increase in the number of the circulating hemocytes that kill parasitoids. However, the different species achieve this in different ways, with D. melanogaster moving sessile hemocytes into circulation while the other species simply produce more cells. Therefore, the convergent evolution of the immune phenotype has different developmental bases. These changes are costly, as resistant populations of all three species had greatly reduced larval survival. In all three species resistance is only costly when food is in short supply, and resistance was rapidly lost from D. melanogaster populations when food is restricted. Furthermore, evolving resistance to L. boulardi resulted in cross-resistance against other parasitoids. Therefore, whether a population evolves resistance will depend on ecological conditions including food availability and the presence of different parasite species.
生物医学研究的一个重点是了解感染易感性差异的原因。为了在一个模型系统中研究基因变异，我们使用了从三种不同果蝇单一群体中收集的果蝇，并对它们进行人工选择，使其对寄生蜂巴氏柔茧蜂具有抗性，结果发现存活率在6代内提高了3至30倍。所有这三个物种的抗性都涉及到循环血细胞数量的大幅增加，这些血细胞会杀死寄生蜂。然而，不同的物种以不同的方式实现这一点，黑腹果蝇将固定的血细胞转移到循环中，而其他物种只是简单地产生更多细胞。因此，免疫表型的趋同进化具有不同的发育基础。这些变化是有代价的，因为所有三个物种的抗性群体幼虫存活率都大幅降低。在所有三个物种中，只有在食物短缺时抗性才会有代价，当食物受到限制时，黑腹果蝇群体的抗性会迅速丧失。此外，进化出对巴氏柔茧蜂的抗性会导致对其他寄生蜂的交叉抗性。因此，一个群体是否进化出抗性将取决于生态条件，包括食物供应情况和不同寄生虫物种的存在。
