Data from: Genotype specificity among hosts, pathogens, and beneficial microbes influences the strength of symbiont mediated protection

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 co-evolution with their host and/or their host's parasites.真核生物的微生物共生体在诸多宿主-寄生虫系统中可调控宿主的抗病性。共生体的基因型与表型均存在显著变异，但目前学界尚未明确自然选择是如何维持这类变异的。此外，自然种群中存在变异的共生菌基因型是否会与宿主或寄生虫的基因型形成特异性关联，这一问题也尚无定论。基因型×基因型互作是交互物种间发生协同进化的必要前提。因此，解析宿主、共生体与寄生虫三者间的遗传特异性模式，对于明确共生体在宿主-寄生虫协同进化中所发挥的作用至关重要。本研究发现，蚜虫的一种垂直传播共生体对真菌病原体的保护效力，同时受宿主-共生体以及共生体-病原体的基因型×基因型互作影响。进一步研究表明，部分共生菌系统发育支系已演化出对特定病原菌基因型更强的保护能力。但本研究未发现共存的宿主与共生菌谱系存在互惠适应的证据。本研究结果提示，共生菌菌株间的遗传变异，或许可通过其与宿主或宿主寄生虫的拮抗协同进化得以维持。