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.昆虫的生态关键性状往往受到兼性细菌内共生体（facultative bacterial endosymbionts）的影响。该类共生体的研究以豌豆蚜（Acyrthosiphon pisum）最为深入：豌豆蚜常被8种兼性共生菌中的一种或多种侵染。目前已有研究证实，多数此类共生菌可赋予宿主一项生态益处，但我们对单一菌株所能产生的全部效应范围仍知之甚少。本研究针对新近发现的X型菌（肠杆菌科，Enterobacteriaceae）的3个菌株展开，阐述各菌株赋予宿主的表型特征；各菌株均存在于其原生的豌豆蚜基因型中，该基因型同时携带螺原体（Spiroplasma）共生体。本研究的所有对照均设置为：一组为同时感染螺原体与X型菌的豌豆蚜，另一组为仅携带螺原体的同基因型豌豆蚜。研究结果显示，在所有试验组中，X型菌感染均可使豌豆蚜抵御致死性真菌病原蚜霉菌（Pandora neoaphidis）；且在2个菌株组中，豌豆蚜对寄生蜂蚜虫茧蜂（Aphidius ervi）的抗性也有所提升。此外，X型菌还可影响豌豆蚜的应激响应：当豌豆蚜经历热胁迫后，携带X型菌的个体繁殖能力有所增强。3个X型菌菌株中有2个可同时提供上述全部益处。而在温和环境条件下，携带X型菌的豌豆蚜的繁殖力往往有所下降，这一机制或许可解释该共生菌在野外种群中维持中等频率的原因。上述研究结果表明，单一兼性内共生菌株具备为其蚜虫宿主提供多种生态益处的潜力。