title: A parasite's modification of host behavior reduces predation on its host.
abstract: Parasite modification of host behavior is common, and the literature is dominated by demonstrations of enhanced predation on parasitized prey resulting in transmission of parasites to their next host. We present a case in which predation on parasitized prey is reduced. Despite theoretical modeling suggesting that this phenomenon should be common, it has been reported in only a few host-parasite-predator systems. Using a system of gregarine endosymbionts in host mosquitoes, we designed experiments to compare the vulnerability of parasitized and unparasitized mosquito larvae to predation by obligate predatory mosquito larvae and then compared behavioral features known to change in the presence of predatory cues. We exposedAedes triseriatuslarvae to the parasiteAscogregarina barrettiand the predatorToxohrynchites rutilusand assessed larval mortality rate under each treatment condition. Further, we assessed behavioral differences in larvae due to infection and predation stimuli by recording larvae and scoring behaviors and positions within microcosms. Infection with gregarines reduced cohort mortality in the presence of the predator, but the parasite did not affect mortality alone. Further, infection by parasites altered behavior such that infected hosts thrashed less frequently than uninfected hosts and were found more frequently on or in a refuge within the microcosm. By reducing predation on their host, gregarines may be acting as mutualists in the presence of predation on their hosts. These results illustrate a higher-order interaction, in which a relationship between a species pair (host-endosymbiont or predator-prey) is altered by the presence of a third species.
authors.affiliation: Department of Biology Clark University Worcester MA USA; Department of Environmental Science The Connecticut Agricultural Experiment Station New Haven CT 06511 USA.
authors.forename: John
authors.identifier: 0000-0003-4469-2072
authors.initials: J
authors.lastname: Soghigian
authors.affiliation: Department of Biology Clark University Worcester MA USA.
authors.forename: Linda R
authors.initials: LR
authors.lastname: Valsdottir
authors.affiliation: Department of Biology Clark University Worcester MA USA.
authors.forename: Todd P
authors.initials: TP
authors.lastname: Livdahl
keywords: Aedes triseriatus; Ascogregarina; Toxorhynchites; higher‐order interaction; host–parasite interactions; mosquito; predator–prey interactions