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

在与天敌的战斗中，长期以来，人们一直认为动物可以自己防御。然而，最近的研究结果表明，一些细菌依赖于微生物共生体的防御服务。例如，豌豆蚜虫通过母体传播的共生体保护它们免受寄生蜂的侵袭，寄生蜂被用作这些作物害虫的生防剂。在评估对黄蜂的抗性差异时，遗传差异似乎是由细菌防御性汉密尔顿共生体的存在及其携带的毒素编码噬菌体(病毒)的类型所驱动的。尽管这些防御成分带来了显著的好处，但它们在自然蚜虫种群中的存在并不普遍，这表明在某些情况下感染成本和防御效率低下。在这项研究中，研究人员建议探索在防御性共生体存在的情况下导致自然变化的力量，检查温度和寄生水平对共生体流行率的影响。将通过广泛的现场和分子研究，量化温度以及共生菌和寄生虫在空间和时间上的流行情况，来检验共生菌频率因高温和罕见的寄生虫而降低的预测。类似的方法将被用来测试共生体在自然条件下的益处。此外，研究人员将阐明防御机制，重点放在预计会导致耐药性变异的噬菌体毒素上。这项工作的发现将确定这些物种的相互作用预计将如何随着全球气温的上升而变化。他们还将通过识别作物害虫用来克服寄生的机制，帮助设计更有效的生物防治计划。这项研究将培养两名研究生和几名本科生。通过在科学会议上发表和展示，以及通过整合到本科课程中，研究人员将通过传统和新的方法传播调查结果。

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.