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

We found evidence that a nematode (Skrjabinoclava morrisoni)adaptivelymanipulates the behavior of its intermediate host (the amphipodCorophiumvolutator) to increase its likelihood of transmission toitsfinal host (the semipalmated sandpiper, Calidris pusilla). Wefoundthat male and female amphipods parasitized by nematodes increasedtheirsurface activity in the field during daytime, but notduring nighttime hours.Increased surface activity is knownto increase susceptibility of amphipods topredation by sandpipersduring the day, but not at night, when sandpipers donot feedvisually. Also, as predicted by the manipulation hypothesis,onlylate-stage (infective) larvae of nematodes were associatedwith behavioralchanges of amphipods. We found no evidence thatparasites were associated withother amphipod behaviors in thelaboratory, such as trail complexity, distancetraveled, orburrow-probing activity of crawling males as would be expectedifparasitized hosts altered their own behavior. Survivorshipof amphipods wasalso unaffected by parasitism, which may favorparasite transmission. Thus,behavioral changes of parasitizedhosts were simple, and their expression wascontext-dependentand related to likelihood of predation. We argue thatmaturationtimes of nematodes in relation to migration schedules of sandpipersprovidea narrow window of opportunity and may explain why nematodesmanipulateamphipod behavior.