Despite their ubiquity and considerable biomass, the roles played by parasites in aquatic food webs are still not well understood, especially those of their free-living infectious stages. For instance, cercariae, the motile larvae of parasitic flukes (trematodes) may be a key source of nutrients and energy for consumers. As cercariae clonally reproduce within the digestive-gonadal gland complex of gastropod intermediate hosts that acquire nutritionally important polyunsaturated fatty acids (PUFA) mainly from their diets (e.g., by grazing on primary producers), cercariae could transfer snail-derived PUFA if consumed. Through fatty acid (FA) analysis, we explored whether a change in the diet of parasitized hosts altered the FA profiles of both snail-only and trematode-containing snail tissue, thereby affecting their nutritional values. Freshwater snails (Stagnicola elodes) infected with Plagiorchis sp. were fed three different diets (cyanobacteria, green algae, and diatoms) that differed in nutritional quality with respect to FA profiles. While diet influenced the overall FA composition of both snail-only tissue and snail tissue containing trematodes, levels of certain PUFA (mainly omega-3) were largely unaffected. Trematode-containing snail tissue also generally contained more PUFA relative to snail-only tissue. Notably, both tissue types had far higher levels of PUFA than found in their diets. Our results suggest that freshwater snail hosts, and possibly their associated trematode parasites, could be trophic upgraders of key PUFA despite anthropogenically induced changes in algal communities that may lead to overall diminished PUFA contents. As such, cercariae-mediated trophic transfers of PUFA may play important roles in aquatic food webs.

尽管它们无处不在且具有大量生物量，但寄生虫在水生食物网中所起的作用仍未被很好地理解，尤其是在其自由生活的传染阶段。例如，尾c是寄生吸虫（吸虫）的活动幼虫，可能是消费者养分和能量的主要来源。由于尾c在腹足纲动物的消化性腺腺复合体中克隆繁殖，这些中间宿主主要从饮食中获取营养重要的多不饱和脂肪酸（PUFA）（例如，通过在初级生产者身上放牧），因此，尾if可以通过食用蜗牛衍生的PUFA。通过脂肪酸（FA）分析，我们探讨了寄生寄主宿主饮食的变化是否改变了仅蜗牛和含有吸虫的蜗牛组织的FA分布，从而影响了它们的营养价值。Stagnicola elodes）感染了Plagiorchissp。饲喂三种不同的饮食（蓝藻，绿藻和硅藻），这些饮食的营养品质在FA方面有所不同。饮食会影响纯蜗牛组织和含有吸虫的蜗牛组织的整体FA组成，但某些PUFA（主要是omega-3）的水平在很大程度上不会受到影响。相对于仅使用蜗牛的组织，含吸虫的蜗牛组织通常还含有更多的PUFA。值得注意的是，两种组织类型的PUFA含量都比饮食中高得多。我们的研究结果表明，尽管人为诱发的藻类群落变化可能导致PUFA含量总体下降，但淡水蜗牛寄主以及可能与之相关的气管吸虫寄生虫可能是关键PUFA的营养改良剂。因此，