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 the intensity of
anthropogenic disturbance, thus providing 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 generalised 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.