Data from: A facultative endosymbiont in aphids can provide diverse ecological benefits

Ecologically important traits of insects are often affected by facultative bacterial endosymbionts. This is best studied in the pea aphid Acyrthosiphon pisum, which is frequently infected by one or more of eight facultative symbiont species. Many of these symbiont species have been shown to provide one ecological benefit, but we have little understanding of the range of effects that a single strain can have. Here, we describe the phenotypes conferred by three strains of the recently discovered bacterium known as X-type (Enterobacteriaceae), each in their original aphid genotype which also carries a Spiroplasma symbiont. All comparisons are made between aphids at that are coinfected with Spiroplasma and X-type and aphids of the same genotype that harbor only Spiroplasma. We show that in all cases, infection with X-type protects aphids from the lethal fungal pathogen Pandora neoaphidis, and in two cases resistance to the parasitoid Aphidius ervi also increases. X-type can additionally affect aphid stress responses – the presence of X-type increased reproduction after the aphids were heat stressed. Two of the three strains of X-type are able to provide all of these benefits. Under benign conditions the aphids tended to suffer from reduced fecundity when harboring X-type, a mechanism that might maintain intermediate frequencies in field populations. These findings highlight that a single strain of a facultative endosymbiont has the potential to provide diverse benefits to its aphid host.昆虫的生态重要性状常受兼性细菌内共生菌（facultative bacterial endosymbionts）调控。这一现象在豌豆蚜（pea aphid, Acyrthosiphon pisum）中得到了最为深入的研究——该蚜虫常被8种兼性共生菌中的一种或多种侵染。诸多这类共生菌已被证实可提供单一生态益处，但学界对单个菌株所能产生的效应范围仍知之甚少。本研究针对新近发现的、隶属于肠杆菌科（Enterobacteriaceae）的X型细菌的3个菌株展开表型分析，分别在其各自携带螺原体（Spiroplasma）共生菌的原始蚜虫基因型背景下进行。所有比较均在同时感染螺原体与X型的蚜虫与仅携带螺原体的同基因型蚜虫之间展开。研究结果显示，在所有实验案例中，X型侵染均可保护蚜虫免受致死性真菌病原菌新蚜虫疠霉（Pandora neoaphidis）的侵害；在其中2个案例中，蚜虫对寄生蜂艾氏蚜茧蜂（Aphidius ervi）的抗性也显著提升。此外，X型还可影响蚜虫的应激反应：经历热胁迫后，携带X型的蚜虫繁殖能力有所增强。3个X型菌株中有2个可同时提供上述所有益处。在适宜环境条件下，携带X型的蚜虫往往表现出繁殖力下降的特征，这一机制或许可维持该共生菌在野外种群中的中间频率。上述研究结果突显了单个兼性共生菌菌株有可能为其蚜虫宿主带来多样化的生态益处。