Fontes Inês, Hartikainen Hanna, Taylor Nick G H, Okamura Beth
Department of Life Sciences,Natural History Museum,Cromwell Road,London SW7 5BD,UK.
Eawag, Swiss Federal Institute of Aquatic Science and Technology,Dübendorf,Switzerland.
Parasitology. 2017 Jul;144(8):1052-1063. doi: 10.1017/S0031182017000269. Epub 2017 Mar 14.
Colonial hosts offer unique opportunities for exploitation by endoparasites resulting from extensive clonal propagation, but these interactions are poorly understood. The freshwater bryozoan, Fredericella sultana, and the myxozoan, Tetracapsuloides bryosalmonae, present an appropriate model system for examining such interactions. F. sultana propagates mainly asexually, through colony fragmentation and dormant propagules (statoblasts). Our study examines how T. bryosalmonae exploits the multiple transmission routes offered by the propagation of F. sultana, evaluates the effects of such transmission on its bryozoan host, and tests the hypothesis that poor host condition provokes T. bryosalmonae to bail out of a resource that may soon be unsustainable, demonstrating terminal investment. We show that infections are present in substantial proportions of colony fragments and statoblasts over space and time and that moderate infection levels promote statoblast hatching and hence effective fecundity. We also found evidence for terminal investment, with host starvation inducing the development of transmission stages. Our results contribute to a growing picture that interactions of T. bryosalmonae and F. sultana are generally characterized by parasite persistence, facilitated by multiple transmission pathways and host condition-dependent developmental cycling, and host tolerance, promoted by effective fecundity effects and an inherent capacity for renewed growth and clonal replication.
由于广泛的克隆繁殖，群体宿主为内寄生虫提供了独特的寄生机会，但人们对这些相互作用了解甚少。淡水苔藓虫类的苏氏弗雷德里克苔藓虫（Fredericella sultana）和粘孢子虫类的鲑鳟四囊虫（Tetracapsuloides bryosalmonae），为研究此类相互作用提供了一个合适的模型系统。苏氏弗雷德里克苔藓虫主要通过群体分裂和休眠繁殖体（芽球）进行无性繁殖。我们的研究考察了鲑鳟四囊虫如何利用苏氏弗雷德里克苔藓虫繁殖所提供的多种传播途径，评估这种传播对其苔藓虫宿主的影响，并检验以下假设：宿主状况不佳会促使鲑鳟四囊虫放弃一个可能很快变得无法维持的资源，即表现出终极投资行为。我们发现，在空间和时间上，大量的群体片段和芽球中都存在感染情况，而且适度的感染水平会促进芽球孵化，从而提高有效繁殖力。我们还发现了终极投资行为的证据，即宿主饥饿会诱导传播阶段的发育。我们的研究结果有助于呈现出这样一幅越来越清晰的画面：鲑鳟四囊虫与苏氏弗雷德里克苔藓虫之间的相互作用通常具有以下特点，一方面是寄生虫的持续存在，这得益于多种传播途径以及宿主状况依赖的发育循环；另一方面是宿主的耐受性，这是由有效繁殖力效应以及固有的重新生长和克隆复制能力所促进的。
