Parasite infection and predatory stress often simultaneously impact wildlife populations, with potentially complex effects on the traits and fitness of the affected animals. For instance, nonconsumptive predator effects may decrease the ability of a potential prey individual to tolerate intense macroparasite infections. In this study, we examined the responses of green frog (Rana clamitans) larvae to echinostome (Digenea: Echinostomatidae) parasite infection and predator chemical cue. In two aquaria experiments, we measured activity levels, growth, and mortality of larvae after exposure to echinostome cercariae, larval Anax (Odonata) predator cue, or the combination of cercariae and predator cue. Due to the costs associated with each stressor, we predicted that the combination treatment would result in synergistic effects on behavior, growth, and mortality.
Results/Conclusions
As expected, individuals exposed to predator cue showed decreased activity levels and growth in comparison to controls. Exposure to predator cue did not affect mortality. Infected individuals showed decreased activity level and higher mortality, but growth was not affected. Contrary to our predictions, we did not observe an interaction between these stressors with respect to either traits or mortality. These results suggest that, at least at a small scale, we can treat these stressors as additive. However, further studies that incorporate additional interactions between these natural enemies may demonstrate other important synergisms.
