Understanding how populations are structured in space and time is a central question in evolutionary biology. Parasites and their hosts are assumed to evolve together, however, detailed understanding of mechanisms leading to genetic structuring of parasites and their hosts are lacking. As a parasite depends on its host, studying the genetic structure of both parasite and host can reveal important insights into these mechanisms. Here, genetic structure of the monogenean parasite Gyrodactylus thymalli and its host the European grayling (Thymallus thymallus) was investigated in 10 tributaries draining into the large Lake Mjosa in Norway. The population genetic structure of spawning grayling was studied using microsatellite genotyping, while G. thymalli was studied by sequencing a mitochondrial DNA gene (dehydrogenase subunit 5). Two main genetic clusters were revealed in grayling, one cluster comprising grayling from the largest spawning population, while the remaining tributaries formed the second cluster. For both taxa, some genetic differentiation was observed among tributaries, but there was no clear isolation-by-distance signature. The structuring was stronger for the host than for the parasite. These results imply that moderate to high levels of gene flow occur among the sub-populations of both taxa. The high parasite exchange among tributaries could result from a lack of strong homing behavior in grayling as well as interactions among individual fish outside of the spawning season, leading to frequent mixing of both host and parasite.

中文翻译：

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挪威大型湖泊中单系寄生虫 Gyrodactylus thymalli 及其寄主欧洲鳟鱼 (Thymallus thymallus) 的遗传种群结构

了解种群在空间和时间上的结构是进化生物学的一个核心问题。寄生虫及其宿主被假定为共同进化，然而，缺乏对导致寄生虫及其宿主遗传结构的机制的详细了解。由于寄生虫依赖于其宿主，因此研究寄生虫和宿主的遗传结构可以揭示对这些机制的重要见解。在这里，在流入挪威 Mjosa 大湖的 10 条支流中研究了单系寄生虫 Gyrodactylus thymalli 及其宿主欧洲鳟鱼 (Thymallus thymallus) 的遗传结构。使用微卫星基因分型研究产卵鲑鱼的种群遗传结构，而通过对线粒体 DNA 基因（脱氢酶亚基 5）进行测序来研究 G. thymalli。在鲑鱼中发现了两个主要的遗传簇，一个簇包含来自最大产卵种群的鲑鱼，而其余的支流形成了第二个簇。对于这两种分类群，在支流之间观察到了一些遗传分化，但没有明确的距离隔离特征。宿主的结构比寄生虫强。这些结果意味着在两个分类群的亚群中都发生了中到高水平的基因流动。支流之间的高寄生虫交换可能是由于鳟鱼缺乏强烈的归巢行为以及产卵季节之外个体鱼类之间的相互作用，导致宿主和寄生虫频繁混合。而其余的支流则形成了第二个集群。对于这两种分类群，在支流之间观察到了一些遗传分化，但没有明确的距离隔离特征。宿主的结构比寄生虫强。这些结果意味着在两个分类群的亚群中都发生了中到高水平的基因流动。支流之间的高寄生虫交换可能是由于鳟鱼缺乏强烈的归巢行为以及产卵季节之外个体鱼类之间的相互作用，导致宿主和寄生虫频繁混合。而其余的支流则形成了第二个集群。对于这两种分类群，在支流之间观察到了一些遗传分化，但没有明确的距离隔离特征。宿主的结构比寄生虫强。这些结果意味着在两个分类群的亚群中都发生了中到高水平的基因流动。支流之间的高寄生虫交换可能是由于鳟鱼缺乏强烈的归巢行为以及产卵季节之外个体鱼类之间的相互作用，导致宿主和寄生虫频繁混合。这些结果意味着在两个分类群的亚群中都发生了中到高水平的基因流动。支流之间的高寄生虫交换可能是由于鳟鱼缺乏强烈的归巢行为以及产卵季节之外个体鱼类之间的相互作用，导致宿主和寄生虫频繁混合。这些结果意味着在两个分类群的亚群中都发生了中到高水平的基因流动。支流之间的高寄生虫交换可能是由于鳟鱼缺乏强烈的归巢行为以及产卵季节之外个体鱼类之间的相互作用，导致宿主和寄生虫频繁混合。