Parker Benjamin J, Hrček Jan, McLean Ailsa H C, Godfray H Charles J
Department of Zoology, University of Oxford, Oxford, OX1 3PS, United Kingdom.
Current Address: Department of Biology, University of Rochester, Rochester, NY, 14627, USA.
Evolution. 2017 May;71(5):1222-1231. doi: 10.1111/evo.13216. Epub 2017 Mar 24.
The microbial symbionts of eukaryotes influence disease resistance in many host-parasite systems. Symbionts show substantial variation in both genotype and phenotype, but it is unclear how natural selection maintains this variation. It is also unknown whether variable symbiont genotypes show specificity with the genotypes of hosts or parasites in natural populations. Genotype by genotype interactions are a necessary condition for coevolution between interacting species. Uncovering the patterns of genetic specificity among hosts, symbionts, and parasites is therefore critical for determining the role that symbionts play in host-parasite coevolution. Here, we show that the strength of protection conferred against a fungal pathogen by a vertically transmitted symbiont of an aphid is influenced by both host-symbiont and symbiont-pathogen genotype by genotype interactions. Further, we show that certain symbiont phylogenetic clades have evolved to provide stronger protection against particular pathogen genotypes. However, we found no evidence of reciprocal adaptation of co-occurring host and symbiont lineages. Our results suggest that genetic variation among symbiont strains may be maintained by antagonistic coevolution with their host and/or their host's parasites.
真核生物的微生物共生体在许多宿主 - 寄生虫系统中影响抗病性。共生体在基因型和表型上都表现出显著的变异，但尚不清楚自然选择如何维持这种变异。在自然种群中，可变的共生体基因型是否与宿主或寄生虫的基因型表现出特异性也不清楚。基因型间的相互作用是相互作用物种之间协同进化的必要条件。因此，揭示宿主、共生体和寄生虫之间的遗传特异性模式对于确定共生体在宿主 - 寄生虫协同进化中所起的作用至关重要。在这里，我们表明，蚜虫的一种垂直传播的共生体对真菌病原体的保护强度受到宿主 - 共生体以及共生体 - 病原体基因型间相互作用的影响。此外，我们表明某些共生体系统发育分支已经进化到能够针对特定病原体基因型提供更强的保护。然而，我们没有发现同时出现的宿主和共生体谱系相互适应的证据。我们的结果表明，共生体菌株之间的遗传变异可能通过与其宿主和/或宿主的寄生虫的拮抗协同进化来维持。
