Evidence that the parasitic nematode Skrjabinoclava manipulates host Corophium behavior to increase transmission to the sandpiper, Calidris pusilla

Abstract

We found evidence that a nematode (Skrjabinoclava morrisoni) adaptively manipulates the behavior of its intermediate host (the amphipod Corophium volutator) to increase its likelihood of transmission to its final host (the semipalmated sandpiper, Calidris pusilla). We found that male and female amphipods parasitized by nematodes increased their surface activity in the field during daytime, but not during nighttime hours. Increased surface activity is known to increase susceptibility of amphipods to predation by sandpipers during the day, but not at night, when sandpipers do not feed visually. Also, as predicted by the manipulation hypothesis, only late-stage (infective) larvae of nematodes were associated with behavioral changes of amphipods. We found no evidence that parasites were associated with other amphipod behaviors in the laboratory, such as trail complexity, distance traveled, or burrow-probing activity of crawling males as would be expected if parasitized hosts altered their own behavior. Survivorship of amphipods was also unaffected by parasitism, which may favor parasite transmission. Thus, behavioral changes of parasitized hosts were simple, and their expression was context-dependent and related to likelihood of predation. We argue that maturation times of nematodes in relation to migration schedules of sandpipers provide a narrow window of opportunity and may explain why nematodes manipulate amphipod behavior.