Infection with a trematode parasite differentially alters competitive interactions and antipredator behavior in native and invasive crayfishes
Parasites can have profound impacts on host behavior and the behavioral interactions between species. Trematode parasites (Microphallus sp.) were identified in three common crayfishes that inhabit northern Wisconsin lakes. Prevalence of these parasites has been associated with crayfish population declines; however, the mechanisms by which Microphallus may reduce crayfish fitness remain largely unexplored. Crayfish are an intermediate host for Microphallus, and this parasite must be consumed by a predator for it to complete its life cycle. One of the three crayfish, Orconectes virilis, is native to northern Wisconsin, while the other two species, O. propinquus and O. rusticus, are non-indigenous to the region and have major impacts on lake communities. We expected Microphallus to have different behavioral effects on each species because it likely shares a longer coevolutionary history with one congener. As crayfish avoid predation largely by utilizing shelter, we collected infected and uninfected crayfish of all three species from the field and examined their shelter use in laboratory experiments in the presence and absence of a conspecific. We also tested crayfish behavior (boldness) in the presence of a predator by quantifying how quickly crayfish emerged from shelter with a predatory fish present.
Infection with Microphallus substantially altered crayfish shelter use, shelter competition, and response to predatory fish, and as we predicted, infection had a different effect on each species. Infection reduced the time that native O. virilis spent in shelter by 15%, reduced the time that O. propinquus spent in shelter by 40%, and did not alter O. rusticus shelter use. Infection also reduced the ability of O. virilis to compete for shelter against an uninfected conspecific. Although infected O. propinquus spent less time in shelter when alone, these crayfish were more likely to win a competition for shelter against an uninfected conspecific. Infection did not alter competitive ability in O. rusticus. In the presence of a fish predator, infection did not alter boldness behavior in O. virilis; however, both O. propinquus and O. rusticus emerged from shelter more rapidly when infected (by 68% and 55% respectively). O. propinquus is likely to suffer the greatest increase in predation when infected due to dramatically reduced shelter use coupled with increased boldness. Overall, these changes in behavior are likely to make all three species more vulnerable to predation and are consistent with behavioral manipulation by Microphallus to increase transmission to higher trophic levels.