Understanding the causes and consequences of disease outbreaks in organisms requires understanding the role of the environment in shaping parasite-host interactions. Daphnia are exposed to a wide array of phytoplankton and parasites in freshwater ecosystems, and this exposure can vary both spatially and temporally. Plankton also vary both in nutrient quality and secondary metabolites. The chemical arsenal of phytoplankton can confer benefits such as defense against herbivory and other microbes, therefore raising the question whether these metabolites have an effect on Daphnia parasites. We investigated the role of food quality on disease emergence and transmission, as well as the consequences of toxic food consumption by Daphnia on host and parasite fitness.
Results/Conclusions
Results shows that both toxins and nutrient quality can influence disease in Daphnia, but that these effects differ between parasite species. Anabaena, Microcystis and Chlorella diets prevented infection of Daphnia by the fungal parasite Metschnikowia, while Nodularia toxins increased offspring production by infected hosts. In contrast to their medicinal effects against Metschnikowia, toxic algae generally decreased the fitness of Daphnia infected with the bacterial parasite, Pasteuria. Notably, concentrations of anatoxin-a produced by Anabaena increased in the presence of Metschnikowia, suggesting parasite-induced toxin production. This research shows that algae can serve as toxins or medicines for their consumers and strongly influence herbivore fitness in the presence of parasites.