A novel approach to parasite population genetics: experimental infection reveals geographic differentiation, recombination, and host-mediated population structure in Pasteuria ramosa, a model bacterial parasite of Daphnia

The population structure of parasites is central to the ecology and evolution of host-parasite systems. Here, we investigate the population genetics of Pasteuria ramosa, a bacterial parasite of Daphnia. We used natural P. ramosa spore banks from the sediments of two geographically well-separated ponds to experimentally infect a panel of Daphnia magna host clones whose resistance phenotypes were previously known. In this way, we were able to assess the population structure of P. ramosa based on geography, host resistance phenotype and host genotype. Overall, genetic diversity of P. ramosa was high, and nearly all infected D. magna hosted more than one parasite haplotype. On the basis of the observation of recombinant haplotypes and relatively low levels of linkage disequilibrium, we conclude that P. ramosa engages in substantial recombination. Isolates were strongly differentiated by pond, indicating that gene flow is spatially restricted. Pasteuria ramosa isolates within one pond were s...寄生虫的种群结构是宿主-寄生虫系统生态学与演化研究的核心议题。本研究针对寄生在水蚤体内的细菌拉姆氏巴斯德菌（Pasteuria ramosa）开展种群遗传学分析。我们利用两个地理间隔较远的池塘沉积物中留存的天然拉姆氏巴斯德菌孢子库，对一组已知抗性表型的大型溞（Daphnia magna）宿主克隆株开展人工感染实验。借此，我们能够基于地理来源、宿主抗性表型与宿主基因型，评估拉姆氏巴斯德菌的种群结构。整体而言，该菌的遗传多样性较高，且几乎所有被感染的大型溞体内都存在至少两种寄生虫单倍型（haplotype）。基于重组单倍型的观测结果以及相对较低的连锁不平衡（linkage disequilibrium）水平，我们判定拉姆氏巴斯德菌存在大量基因重组现象。不同池塘来源的菌株呈现显著遗传分化，表明其基因流存在空间限制。单个池塘内的拉姆氏巴斯德菌分离株则……