Data from: Horizontal transfer of facultative endosymbionts is limited by host relatedness

Heritable microbial symbionts can have important effects on many aspects of their hosts’ biology. Acquisition of a novel symbiont strain can provide fitness benefits to the host, with significant ecological and evolutionary consequences. We measured barriers to horizontal transmission by artificially transferring facultative symbionts from the grain aphid, Sitobion avenae, and five other aphid species into two clonal genotypes of S. avenae. We found the symbiont Hamiltonella defensa establishes infections more easily following a transfer from the same host species and that such infections are more stable. Infection success was also higher when the introduced symbiont strain was more closely related to the strain that was originally present in the host (but which had previously been removed). There were no differences amongst successfully established symbiont strains in their effect on aphid fecundity. H. defensa did not confer protection against parasitoids in our S. avenae clones, although it often does in other aphid hosts. However, strains of the symbiont Regiella insecticola originating from two host species protected grain aphids against the pathogenic fungus Pandora neoaphidis. This study helps describe the extent to which facultative symbionts can act as a pool of adaptations that can be sampled by their eukaryote hosts.可遗传微生物共生体（heritable microbial symbionts）对宿主生物学的诸多维度均可产生关键影响。获取新型共生菌株可为宿主带来适合度收益，并引发显著的生态学与进化学效应。本研究通过人工转接的方式，将从麦长管蚜（Sitobion avenae）及其他5种蚜虫体内分离得到的兼性共生体（facultative symbionts），转入两个麦长管蚜克隆基因型中，以此测定水平传播的屏障效应。研究发现，当供体共生体来自与受体宿主相同的物种时，防御哈氏菌（Hamiltonella defensa）更易建立感染，且此类感染的稳定性更强。当引入的共生菌株与宿主原有的（已预先清除的）共生菌株亲缘关系越近时，感染成功率也越高。成功定殖的各类共生菌株对蚜虫繁殖力的影响无显著差异。在本研究使用的麦长管蚜克隆株中，防御哈氏菌并未赋予宿主对抗寄生蜂的抗性，尽管该菌在其他蚜虫宿主中通常具备此功能。不过，源自两种宿主的昆虫栖居雷吉菌（Regiella insecticola）菌株，可使麦长管蚜获得抵抗病原真菌新蚜虫疠霉（Pandora neoaphidis）的能力。本研究明确了兼性共生体可作为一类适应性储备库，真核宿主可从中选取适配的共生体，其应用范围由此得以清晰界定。