Classical models of parasite transmission focus on the density of susceptible and infected hosts or stages. However, recent research highlights how transmission success often depends additionally on non-host members of the ecological community, including predators. The predators that consume parasite infectious agents can substantially reduce transmission, highlighting the importance of considering host-parasite interactions within realistic communities. Less clear, however, are the specific conditions of parasites and predators that increase the likelihood of reduced transmission. Here, we take a trait-based approach to improve our ability to predict what combination of predator and parasite traits will lead to high parasite consumption and the potential to ultimately reduce transmission. Using an experimental approach, we exposed five morphotypes of the trematode infectious stages (cercariae) found in freshwater lentic habitats to as many as five aquatic insect taxa to assess the effects of parasite and predator traits on consumption.
Results/Conclusions
Consumption of the infectious cercariae varied substantially across both parasite morphotype and predator identity. Mean consumption rate varied among parasite taxa from <15% to over 40%; among control trials with no predators, an average of 95% of cercariae were detected after the 60 minute assay period. Among predators, consumption varied by roughly four-fold, ranging from 9% (Order: Ephemeroptera; Family: Baetidae) to 38% (Order: Odonata; Family: Coenagrionidae). Including both predator and parasite traits greatly improved our model: both predator body size and cercariae tail size—as well as their interaction—strongly influenced the probability of cercariae being consumed, while small-bodied predators were the most effective consumers. These results reveal that the likelihood of parasite consumption depends on the relative size between predator and parasite. Our study provides a strong foundation to build a predictive framework for what predator and parasite combinations should reduce parasite transmission in natural populations, which has important implications for understanding how infection success depends on the composition of complex ecological communities.