Factors shaping the maintenance of variation in a symbiont-mediated host-enemy interaction

在与天敌的战斗中，人们一直认为动物只能依靠自己的防御。然而，最近的研究结果表明，一些依赖于微生物共生体的防御服务。例如，豌豆蚜虫拥有母体传播的共生体，可以保护它们免受寄生蜂的侵害，寄生蜂被用作对抗这些作物害虫的生物控制剂。当评估对黄蜂Aphidius ervi的抗性变化时，似乎遗传差异是由细菌Hamiltonella defensa共生体的存在和它们所携带的编码毒素的噬菌体（病毒）的类型驱动的。尽管这些防御因素带来了显着的好处，但它们的存在并不普遍存在于自然蚜虫种群中，这表明在某些条件下感染的成本和低效的防御。在这项研究中，研究人员建议探索在防御性共生体存在下自然变异的力量，研究温度和寄生水平对共生体流行的影响。将通过广泛的实地和分子研究，量化温度以及共生体和寄生虫在空间和时间上的流行率，来测试对高温和罕见寄生虫引起的共生体频率降低的预测。类似的方法将用于测试共生体在自然条件下的好处。 此外，研究人员将阐明防御机制，重点是预计将驱动抗性变异的噬菌体毒素。这项工作的结果将确定这些物种的相互作用预计将如何随着全球气温的升高而变化。他们还将通过确定作物害虫克服寄生虫的机制，帮助设计更有效的生物防治方案。这项研究将导致两个研究生和几个本科生的培训。通过在科学会议上发表和演讲，并通过融入本科课程，研究人员将通过传统和新颖的方法传播研究结果。

In the battle against natural enemies, it has long been thought that animals are left to their own defenses. However, recent findings indicate that some rely on the defensive services of microbial symbionts. Pea aphids, for example, harbor maternally transmitted symbionts that defend them against parasitic wasps, which are used as biological control agents against these crop pests. When assessing variation in resistance to the wasp Aphidius ervi, it appears that inherited differences are driven by the presence of bacterial Hamiltonella defensa symbionts and the types of toxin-encoding bacteriophages (viruses) they harbor. Despite significant benefits conferred by these defensive elements, their presence is not universal within natural aphid populations, suggesting costs of infection and inefficient defense under some conditions. In this study, the researchers propose to explore the forces responsible for natural variation in the presence of defensive symbionts, examining the effects of temperature and levels of parasitism on symbiont prevalence. Predictions of reduced symbiont frequencies in response to high temperatures and infrequent parasitism will be tested through extensive field-based and molecular studies that quantify temperature and both symbiont and parasite prevalence over space and time. Similar approaches will be used to test the benefits of symbionts under natural conditions. Additionally, the investigators will elucidate the mechanisms of defense, focusing on the bacteriophage toxins that are expected to drive variation in resistance. Findings from this work will determine how these species interactions are expected to change with increasing global temperatures. They will also help in the design of more effective biological control programs, through identifying the mechanisms that crop pests employ to overcome parasitism. This research will result in the training of two graduate and several undergraduate students. Through publication and presentation at scientific meetings, and through integration into undergraduate coursework, the investigators will disseminate the findings through both traditional and novel approaches.