The Implications of Parasite Roles for the Nutritional Dynamics of Food Webs

It is increasingly evident that the aquatic free-living infectious stages (cercariae) of trematodes (flatworms) serve as dietary sources and vectors of nutritionally-important polyunsaturated fatty acids (PUFA) from their molluscan intermediate hosts to higher trophic-level consumers. Here, I investigated whether a change in the algal diets of trematode-infected snails altered the fatty acid (FA) profiles of these hosts or their parasites, thereby affecting their nutritional values. While diet influenced their overall FA profiles, levels of certain essential fatty acids (EFA) were largely unaffected. This suggests that cercariae-mediated trophic transfers of EFA may not be dramatically affected by algal community shifts. I also investigated whether platyhelminths have the necessary enzymes for de novo omega-3 (n-3) PUFA biosynthesis, and found that select taxa (including prominent trematodes) have the relevant genomic sequences. If these genes are functional, then these parasites may be involved in the natural production of essential n-3 PUFA.