Data from: Geographic variation and trade-offs in parasitoid virulence

Host–parasitoid systems are characterized by a continuous development of new defence strategies in hosts and counter-defence mechanisms in parasitoids. This co-evolutionary arms race makes host–parasitoid systems excellent for understanding trade-offs in host use caused by evolutionary changes in host immune responses and parasitoid virulence. However, knowledge obtained from natural host–parasitoid systems on such trade-offs is still limited. In this study, the aim was to examine trade-offs in parasitoid virulence in Asecodes parviclava (Hymenoptera: Eulophidae) when attacking three closely related beetles: Galerucella pusilla, Galerucella calmariensis and Galerucella tenella (Coleoptera: Chrysomelidae). A second aim was to examine whether geographic variation in parasitoid infectivity or host immune response could explain differences in parasitism rate between northern and southern sites. More specifically, we wanted to examine whether the capacity to infect host larvae differed depending on the previous host species of the parasitoids and if such differences were connected to differences in the induction of host immune systems. This was achieved by combining controlled parasitism experiments with cytological studies of infected larvae. Our results reveal that parasitism success in A. parviclava differs both depending on previous and current host species, with a higher virulence when attacking larvae of the same species as the previous host. Virulence was in general high for parasitoids from G. pusilla and low for parasitoids from G. calmariensis. At the same time, G. pusilla larvae had the strongest immune response and G. calmariensis the weakest. These observations were linked to changes in the larval hemocyte composition, showing changes in cell types important for the encapsulation process in individuals infected by more or less virulent parasitoids. These findings suggest ongoing evolution in parasitoid virulence and host immune response, making the system a strong candidate for further studies on host race formation and speciation.寄主-寄生蜂系统（Host–parasitoid systems）以寄主持续演化新型防御策略、寄生蜂同步演化对应反防御机制为典型特征。这种协同进化军备竞赛（co-evolutionary arms race）使得寄主-寄生蜂系统成为解析宿主免疫响应与寄生蜂毒力演化所介导的宿主利用权衡（trade-offs）的优质研究体系。但目前从自然寄主-寄生蜂系统中获取的关于这类权衡的相关认知仍较为有限。 本研究首要目标为探究小暗脉姬小蜂（Asecodes parviclava，膜翅目: 姬小蜂科（Hymenoptera: Eulophidae)）在攻击三种近缘甲虫时的毒力权衡，这三种甲虫均隶属于鞘翅目: 叶甲科（Coleoptera: Chrysomelidae）萤叶甲属，分别为Galerucella pusilla、Galerucella calmariensis与Galerucella tenella。本研究次要目标为验证：寄生蜂侵染能力或宿主免疫响应的地理变异，是否能够解释南北样地间寄生率的差异。 更为具体地，本研究旨在验证：寄生蜂侵染宿主幼虫的能力是否因自身先前的宿主物种而异，且这类差异是否与宿主免疫系统的诱导差异存在关联。本研究通过将受控寄生实验与感染幼虫的细胞学分析相结合，完成了上述探究。 研究结果表明，小暗脉姬小蜂的寄生成功率同时受先前宿主与当前宿主物种的影响，当其攻击与先前宿主为同一物种的幼虫时，毒力显著更高。总体而言，源自G. pusilla的寄生蜂毒力较高，而源自G. calmariensis的寄生蜂毒力较低。与此同时，G. pusilla幼虫的免疫响应强度最高，G. calmariensis幼虫的免疫响应强度最低。上述观测结果与幼虫血细胞（hemocyte）组成的变化存在关联：在被毒力强弱不同的寄生蜂感染的个体中，与包囊作用（encapsulation）过程密切相关的细胞类型均发生了显著改变。 本研究结果表明，寄生蜂毒力与宿主免疫响应正处于持续演化进程中，该体系也因此成为探究宿主种群分化与物种形成的优质候选研究模型。