Similar cost of Hamiltonella defensa in experimental and natural aphid-endosymbiont associations

Endosymbiont-conferred resistance to parasitoids is common in aphids, but comes at a cost to the host in the absence of parasitoids. In black bean aphids (Aphis fabae), costs in terms of reduced lifespan and lifetime reproduction were demonstrated by introducing eleven isolates of the protective symbiont Hamiltonella defensa into previously uninfected aphid clones. Transfection of H. defensa isolates into a common genetic background allows to compare the costs of different endosymbiont isolates unconfounded by host genetic variation, but has been suggested to overestimate the realised costs of the endosymbiont in natural populations, because transfection creates new and potentially maladapted host-symbiont combinations that would be eliminated by natural selection in the field. In this experiment, we show that removing H. defensa isolates from their natural host clones with antibiotics results in a fitness gain that is comparable to the fitness loss from their introduction into two new ...内共生体赋予蚜虫对拟寄生生物的抗性是蚜虫类群中较为普遍的现象，但在无拟寄生生物胁迫的环境下，该抗性会给宿主带来适合度代价。在蚕豆蚜（Aphis fabae）中，研究人员通过将11株保护性共生体汉密尔顿防御菌（Hamiltonella defensa）导入此前未受感染的蚜虫克隆系，证实了该共生体在宿主寿命与终身繁殖力方面的适合度代价。将汉密尔顿防御菌菌株转染至统一的遗传背景中，能够排除宿主遗传变异的混杂效应，从而实现不同内共生体菌株适合度代价的直接比较，但有研究指出该方法会高估自然种群中内共生体的实际代价：因为转染操作会形成全新的、潜在适配不良的宿主-共生体组合，这类组合在野外环境中会被自然选择所淘汰。本实验证实，通过抗生素将汉密尔顿防御菌从其天然宿主克隆系中清除后，宿主获得的适合度增益，与将该菌株导入两个全新的……