Hrček Jan, Parker Benjamin J, McLean Ailsa H C, Simon Jean-Christophe, Mann Ciara M, Godfray H Charles J
Department of Zoology, University of Oxford, Oxford, OX1 3PS, United Kingdom.
Current address: Czech Academy of Sciences, Biology Centre, Institute of Entomology, Branisovska 31, Ceske Budejovice 37005, Czech Republic.
Evolution. 2018 May 28. doi: 10.1111/evo.13512.
Microbial symbionts commonly protect their hosts from natural enemies, but it is unclear how protective symbionts influence the evolution of host immunity to pathogens. One possibility is that 'extrinsic' protection provided by symbionts allows hosts to reduce investment in 'intrinsic' immunological resistance mechanisms. We tested this idea using pea aphids (Acyrthosiphon pisum) and their facultative bacterial symbionts that increase host resistance to the fungal pathogen Pandora neoaphidis. The pea aphid taxon is composed of multiple host plant associated populations called biotypes, which harbor characteristic communities of symbionts. We found that biotypes that more frequently carry protective symbionts have higher, rather than lower, levels of intrinsic resistance. Within a biotype there was no difference in intrinsic resistance between clones that did and did not carry a protective symbiont. The host plant on which an aphid feeds did not strongly influence intrinsic resistance. We describe a simple conceptual model of the interaction between intrinsic and extrinsic resistance and suggest that our results may be explained by selection favoring both the acquisition of protective symbionts and enhanced intrinsic resistance in habitats with high pathogen pressure. Such combined protection is potentially more robust than intrinsic resistance alone.
微生物共生体通常会保护其宿主免受天敌侵害，但尚不清楚具有保护作用的共生体如何影响宿主对病原体免疫的进化。一种可能性是，共生体提供的“外在”保护使宿主能够减少对“内在”免疫抵抗机制的投入。我们利用豌豆蚜（豌豆蚜）及其兼性细菌共生体进行了测试，这些共生体可增强宿主对真菌病原体新蚜虫疠霉的抵抗力。豌豆蚜分类群由多个与宿主植物相关的种群组成，称为生物型，它们拥有特定的共生体群落。我们发现，更频繁携带保护性共生体的生物型具有更高而非更低的内在抵抗力水平。在一个生物型中，携带和不携带保护性共生体的克隆之间在内在抵抗力上没有差异。蚜虫取食的宿主植物对内在抵抗力没有强烈影响。我们描述了一个内在和外在抵抗力相互作用的简单概念模型，并表明我们的结果可以通过在病原体压力高的栖息地中有利于获取保护性共生体和增强内在抵抗力的选择来解释。这种联合保护可能比单独的内在抵抗力更强大。
