Hartikainen Hanna, Fontes Inês, Okamura Beth
Department of Aquatic Ecology, EAWAG, Überlandstrasse 133, Dübendorf 8600, Switzerland.
Parasitology. 2013 Sep;140(11):1403-12. doi: 10.1017/S0031182013000899.
Changes in host phenotype are often attributed to manipulation that enables parasites to complete trophic transmission cycles. We characterized changes in host phenotype in a colonial host–endoparasite system that lacks trophic transmission (the freshwater bryozoan Fredericella sultana and myxozoan parasite Tetracapsuloides bryosalmonae). We show that parasitism exerts opposing phenotypic effects at the colony and module levels. Thus, overt infection (the development of infectious spores in the host body cavity) was linked to a reduction in colony size and growth rate, while colony modules exhibited a form of gigantism. Larger modules may support larger parasite sacs and increase metabolite availability to the parasite. Host metabolic rates were lower in overtly infected relative to uninfected hosts that were not investing in propagule production. This suggests a role for direct resource competition and active parasite manipulation (castration) in driving the expression of the infected phenotype. The malformed offspring (statoblasts) of infected colonies had greatly reduced hatching success. Coupled with the severe reduction in statoblast production this suggests that vertical transmission is rare in overtly infected modules. We show that although the parasite can occasionally infect statoblasts during overt infections, no infections were detected in the surviving mature offspring, suggesting that during overt infections, horizontal transmission incurs a trade-off with vertical transmission.
宿主表型的变化通常归因于寄生虫为完成营养传播周期而进行的操控。我们对一个缺乏营养传播的群体宿主-内寄生虫系统（淡水苔藓虫弗雷德里克苔藓虫和粘孢子虫寄生虫鲑居尾孢虫）中的宿主表型变化进行了特征描述。我们发现，寄生作用在群体和模块水平上产生了相反的表型效应。因此，显性感染（宿主体腔内感染性孢子的发育）与群体大小和生长速率的降低有关，而群体模块则表现出一种巨型化的形式。更大的模块可能支持更大的寄生虫囊，并增加寄生虫可利用的代谢物。与未投入繁殖体生产的未感染宿主相比，显性感染宿主的代谢率较低。这表明直接资源竞争和寄生虫的主动操控（阉割）在驱动感染表型的表达中发挥了作用。感染群体畸形的后代（休眠芽）孵化成功率大幅降低。再加上休眠芽产量的严重减少，这表明在显性感染的模块中垂直传播很少见。我们发现，虽然寄生虫在显性感染期间偶尔会感染休眠芽，但在存活的成熟后代中未检测到感染，这表明在显性感染期间，水平传播与垂直传播存在权衡。
