Parasite-mediated energy flow across forest and stream ecosystems: proximate mechanisms and ecological consequences

Takuya SATO (Graduate School of Science, Kobe University )

Host manipulation by parasites is among the most fascinating strategies for parasites and is a well-known example of the “Extended Phenotype” in evolutionary biology. Historically, the proximate and ultimate explanations for parasites altering hosts’ phenotypes are of great interest; however, the ecological consequences of the host manipulation for ecosystem processes are only recently gaining attention. Parasitic horsehair hairworms (Nematomorpha) live and mature in terrestrial arthropods, including mantises, orthopterans and coleopterans, but have to reproduce in water. To complete their complex life cycle, horsehair worms induce suicidal behavior of their arthropod hosts, i.e., jumping into water. In riparian ecosystems, orthopteran hosts (camel crickets and some predatory katydids) that jump into water can make up a large proportion of diets of stream fishes, which has cascading effects on ecosystem processes (i.e., algal biomass and detritus processes). Despite this and other examples that the parasites can strongly alter energy flow through food webs, theory has predicted that those parasites are unlikely to persist because they make their intermediate hosts unstable via intensive manipulations. In relation to this paradox, our recently proposed framework suggests that parasites might have evolved more sophisticated ways of host manipulations, which allow both parasites and hosts stably co-exist in terms of trophic dynamics. This framework confronts interdisciplinary research challenges, linking proximate mechanisms and ecological consequences.