Ecological impacts of agrochemical and pharmaceutical antifungals on a non-target aquatic host-parasite model

Agrochemical fungicides and their pharmaceutical counterparts are a major anthropogenic threat to the biodiversity of freshwater ecosystems as they affect non-target organisms (including aquatic fungi) and disrupt the processes in which they intervene. The goal of this work was to assess the effects of four common agricultural fungicides differing in their modes of action (azoxystrobin, carbendazim, folpet, and mancozeb) and an antifungal pharmaceutical (clotrimazole) on a host × parasite experimental model. We conducted 21-day life history experiments with Daphnia magna (the host) in the absence or presence of Metschnikowia bicuspidata (a microparasitic yeast) to evaluate the effect of each fungicide on the outcome of this relationship (disease) and the fitness of both host and parasite. Interactive but context-dependent effects were observed in D. magna life history responses upon concomitant exposure to parasite and toxicant. The parasite had a drastic negative effect on host survival and reproduction. Carbendazim, clotrimazole and folpet significantly decreased host fitness. In some cases (depending on the combination of toxicant and measured endpoint), simultaneous exposure of the host to the parasite and fungicides led to a slight decrease in host reproduction, which was absent when only the fungicide was present. In two other cases, the fungicide interfered with the host-parasite relationship: azoxystrobin had an impact on infection intensity (decreasing spore load per host), whereas clotrimazole demonstrated a strong antiparasitic effect, clearing all signs of infection (0 % prevalence). These findings emphasize the context-dependent nature of the interaction between pollution and disease.