Agricultural land use and ensuing eutrophication both shape parasitic trematode communities in rural African lakes.

Land use is a major driver of biodiversity loss, but how it impacts parasite communities is scarcely documented. Crater lakes and their catchments in rural western Uganda greatly vary in their intensity of anthropogenic disturbance, thus providing an opportunity to assess the effects of land use on snail-borne parasitic trematodes. We applied state-of-the-art molecular biomonitoring to 2385 Bulinus tropicus snails from 34 lakes to detect and genotype trematode infections. The 45 trematode taxa recovered infect a wide range of final vertebrate hosts, and some can cause health burdens of significant public importance. Using constrained ordinations and generalized additive models, we found that B. tropicus reaches peak abundance in lakes with catchments partly under agriculture, whereas trematode infections increase with B. tropicus abundance and peak at intermediate aquatic productivity. Trematode diversity also increases with aquatic productivity, levelling off only in the most productive lakes. These relationships likely reflect the higher abundance and variety of final hosts sustained by more productive lakes. Finally, we found that land use affects trematode community composition, with more livestock parasites and less bird parasites occurring in agricultural catchments. Our results indicate that both land use and lake eutrophication affect the distribution of hotspots for parasitic disease transmission.