Fate by Infection: Quantifying Host Behavioral Changes in Response to Four Variables of Trematode Infection

Although the importance of host-parasite interactions is increasingly recognized, few studies examine factors regulating how infection alters host behavior and the consequences of parasite-induced behavioral changes for predation risk. The present study assessed how infection by trematodes (parasitic flatworms) altered larval amphibian activity and whether these effects depended on trematode species, infection intensity, time post-infection, and/or host size. To examine the implications of these results for tadpole susceptibility to predation, we evaluated how infection by the most virulent trematode altered tadpole escape distance from a simulated predator. Of three trematodes (Echinostoma trivolvis, Ribeiroia ondatrae and Alaria), only R. ondatrae significantly reduced activity of Chorus frog tadpoles (Pseudacris regilla) one day after exposure to 40 cercariae (larval trematodes). Increased R. ondatrae exposure correlated with decreased host activity, especially in smaller hosts. Whether hosts were exposed to acute or chronic parasite infections influenced recovery time to normal activity. Hosts exposed to parasites in a one-time pulse returned to normal activity within five days post-infection, whereas those exposed to smaller doses of parasites daily maintained reduced activity levels for five days. Finally, infection by R. ondatrae reduced host escape distance from a simulated predator in a dose-dependent manner, suggesting that trematode infection could increase predation susceptibility. These results show that significant components of host behavior, including activity levels and predator avoidance, are affected by parasite infection in a manner dependent on dose, parasite identity and host traits. This underscores the significant role of parasite infection in changing host behavior and consequently species interactions