Data from: Effects of parasitism on aphid nutritional and protective symbioses

Insects often carry heritable symbionts that negotiate interactions with food plants or natural enemies. All pea aphids, Acyrthosiphon pisum, require infection with the nutritional symbiont Buchnera, and many are also infected with Hamiltonella, which protects against the parasitoid Aphidius ervi. Hamiltonella-based protection requires bacteriophages called APSEs with protection levels varying by strain and associated APSE. Endoparasitoids, including A. ervi, may benefit from protecting the nutritional symbiosis and suppressing the protective one, while the aphid and its heritable symbionts have aligned interests when attacked by the wasp. We investigated the effects of parasitism on the abundance of aphid nutritional and protective symbionts. First, we determined strength of protection associated with multiple symbiont strains and aphid genotypes as these likely impact symbiont responses. Unexpectedly, some A. pisum genotypes cured of facultative symbionts were resistant to parasitism and resistant aphid lines carried Hamiltonella strains that conferred no additional protection. Susceptible aphid clones carried protective strains. qPCR estimates show that parasitism significantly influenced both Buchnera and Hamiltonella titres, with multiple factors contributing to variation. In susceptible lines, parasitism led to increases in Buchnera near the time of larval wasp emergence consistent with parasite manipulation, but effects were variable in resistant lines. Parasitism also resulted in increases in APSE and subsequent decreases in Hamiltonella, and we discuss how this response may relate to the protective phenotype. In summary, we show that parasitism alters the within-host ecology of both nutritional and protective symbioses with effects likely significant for all players in this antagonistic interaction.

昆虫通常携带可遗传共生菌，这些共生菌介导昆虫与寄主植物或天敌之间的相互作用。所有豌豆蚜（Acyrthosiphon pisum）均需感染营养共生菌布赫纳菌（Buchnera），多数个体还会感染汉森菌（Hamiltonella），后者可抵御寄生蜂Aphidius ervi。基于汉森菌的防御作用需要一种名为APSE的噬菌体，其防御效果因菌株及所关联的APSE而异。内寄生蜂（包括A. ervi）可通过保护营养共生关系、抑制保护性共生关系来获益；而当遭到寄生蜂攻击时，蚜虫与其可遗传共生菌的进化利益是一致的。本研究探究了寄生作用对蚜虫营养共生菌与保护性共生菌丰度的影响。首先，我们测定了多种共生菌菌株与蚜虫基因型所关联的防御强度，因为这些因素可能会影响共生菌的响应模式。出乎意料的是，部分去除了兼性共生菌的豌豆蚜基因型仍可抵御寄生，且具有抗性的蚜虫品系所携带的汉森菌菌株无法提供额外防御；而易受寄生的蚜虫克隆株则携带具有防御作用的汉森菌菌株。定量聚合酶链式反应（qPCR, quantitative PCR）检测结果显示，寄生作用会显著影响布赫纳菌与汉森菌的滴度，且存在多种因素导致丰度变异。在易受寄生的品系中，寄生作用会在寄生蜂幼虫羽化阶段附近导致布赫纳菌丰度上升，这与寄生蜂的宿主操纵现象一致；但在抗性品系中，该效应存在差异。寄生作用还会导致APSE丰度上升，随后汉森菌丰度下降，本研究还讨论了该响应与蚜虫防御表型之间的潜在关联。综上，本研究证实寄生作用会改变营养共生与保护性共生的宿主内生态，其效应可能对该拮抗互作中的所有参与者均具有重要意义。