Data from: Breakdown of a defensive symbiosis, but not endogenous defenses, at elevated temperatures

Environmental factors, including temperature, can have large effects on species interactions, including mutualisms and antagonisms. Most insect species are infected with heritable bacterial symbionts with many protecting their hosts from natural enemies. However, many symbionts or their products are thermally sensitive hence their effectiveness may vary across a range of temperatures. In the pea aphid, Acyrthosiphon pisum, the bacterial symbiont Hamiltonella defensa, and its associated APSE bacteriophages confer resistance to this aphid’s dominant parasitoid, Aphidius ervi. Here we investigate the effects of temperature on both endogenous and symbiont-based protection against this parasitoid. We also explored the defensive properties of the X-type symbiont, a bacterium hypothesized to shape aphid defense when co-occurring with H. defensa. We show that H. defensa protection fails at higher temperatures, although some aphid genotype and H. defensa strain combinations are more robust than others at moderately warmer temperatures. We also found that a single X-type strain neither defended against parasitism by A. ervi nor rescued lost H. defensa protection at higher temperatures. In contrast, endogenous aphid resistance was effective across temperatures, revealing that these distinct defensive modes are not equally robust to changing environments. Through a survey of field-collected pea aphids we found a negative correlation between H. defensa frequencies and average daily temperatures across North American locales, fitting expectations for reduced symbiont benefits under warm climates. Based on these findings, we propose that rising global temperatures could promote the widespread breakdown of defensive mutualisms, a prospect with implications for both human and ecosystem health.环境因子（包括温度）会对物种间相互作用产生显著影响，涵盖互利共生与拮抗作用两大类型。绝大多数昆虫物种均携带遗传性细菌共生菌，其中诸多共生菌可为宿主提供针对天敌的保护。然而，多数共生菌或其代谢产物具有热敏感性，因此其防御效能会随温度区间的变化而发生波动。在豌豆蚜（Acyrthosiphon pisum）中，汉密尔顿氏防御菌（Hamiltonella defensa）及其伴随的APSE噬菌体（APSE bacteriophages），可帮助该蚜虫抵御其主要寄生性天敌麦蚜茧蜂（Aphidius ervi）。本研究探讨了温度在两个维度上对该寄生性天敌抵御效果的影响：一是蚜虫自身的内源防御，二是基于共生菌的防御。此外，本研究还对X型共生菌的防御特性展开了探究——这类细菌被推测可在与汉密尔顿氏防御菌共存时，调控蚜虫的防御表型。研究结果表明，汉密尔顿氏防御菌介导的防御作用在高温环境下会失效，但部分豌豆蚜基因型与汉密尔顿氏防御菌菌株的组合，在适度升温条件下的防御稳定性要强于其他组合。同时本研究还发现，单一的X型共生菌菌株既无法抵御麦蚜茧蜂的寄生，也无法在高温环境下恢复因高温丧失的汉密尔顿氏防御菌防御功能。与之形成对比的是，蚜虫的内源防御在所有测试温度区间内均能发挥有效作用，这表明不同的防御模式对环境变化的耐受能力并不均等。通过对野外采集的豌豆蚜种群进行调查，本研究发现北美各地区豌豆蚜体内汉密尔顿氏防御菌的携带频率与当地日均气温呈负相关关系，这与温暖气候下共生菌防御效能下降的理论预期相符。基于上述研究结果，本研究提出：全球气温上升可能会引发防御性互利共生关系的大范围解体，这一前景对人类健康与生态系统健康均具有重要影响。