Institute of Integrative Biology, ETH Zürich, Universitätstrasse 16, 8092 Zürich; EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland.
Insect Sci. 2014 Jun;21(3):251-64. doi: 10.1111/1744-7917.12067. Epub 2014 Feb 14.
Aphids may harbor a wide variety of facultative bacterial endosymbionts. These symbionts are transmitted maternally with high fidelity and they show horizontal transmission as well, albeit at rates too low to enable infectious spread. Such symbionts need to provide a net fitness benefit to their hosts to persist and spread. Several symbionts have achieved this by evolving the ability to protect their hosts against parasitoids. Reviewing empirical work and some models, I explore the evolutionary ecology of symbiont-conferred resistance to parasitoids in order to understand how defensive symbiont frequencies are maintained at the intermediate levels observed in aphid populations. I further show that defensive symbionts alter the reciprocal selection between aphids and parasitoids by augmenting the heritable variation for resistance, by increasing the genetic specificity of the host-parasitoid interaction, and by inducing environment-dependent trade-offs. These effects are conducive to very dynamic, symbiont-mediated coevolution that is driven by frequency-dependent selection. Finally I argue that defensive symbionts represent a problem for biological control of pest aphids, and I propose to mitigate this problem by exploiting the parasitoids' demonstrated ability to rapidly evolve counteradaptations to symbiont-conferred resistance.
蚜虫可能携带有各种各样的兼性细菌内共生体。这些共生体通过母系遗传以高度保真度传递，并且它们也表现出水平传播，尽管传播速度太低，不足以实现传染性传播。这些共生体需要为它们的宿主提供净适应度优势才能持续存在和传播。一些共生体通过进化出保护宿主免受寄生虫侵害的能力来实现这一点。通过回顾实证工作和一些模型，我探讨了共生体赋予寄生虫抗性的进化生态学，以了解在蚜虫种群中观察到的中间水平上，防御性共生体的频率是如何维持的。我进一步表明，防御性共生体通过增加抗性的可遗传性变异、增加宿主-寄生虫相互作用的遗传特异性以及诱导环境依赖的权衡，改变了蚜虫和寄生虫之间的相互选择。这些效应有利于由频率依赖选择驱动的非常动态的、共生介导的协同进化。最后，我认为防御性共生体对生物防治害虫蚜虫构成了一个问题，并建议利用寄生虫已经证明的快速进化出对共生体赋予的抗性的反适应能力来减轻这个问题。
