A transmissible trematode affects the direction and rhythm of movement in a marine gastropod.
Microphallus piriformes (Trematoda) is unusual in having only two hosts and no motile free-living stages. The intermediate host, the rough periwinkle, Littorina saxatilis, is present year-round on rocky shores and has a high parasite prevalence near breeding colonies of the definitive host, the herring gull, Larus argentatus, which is present in numbers at these sites for only 4 months per year. Given the seasonal availability of gulls for infection and a low incidence of periwinkles in the normal diet of herring gulls, specialized transmission between stages appears necessary for maintenance of the parasite's life cycle. We investigated the hypothesis that M. piriformes alters its intermediate host's behaviour during the gull's breeding season in a manner that may facilitate predation of the infected periwinkle by breeding gulls. We studied the movements of periwinkles during simulated tidal cycles in the laboratory; parasite status was established subsequently. Periwinkles with mature infections moved further upwards but showed less downwards and horizontal movement than uninfected periwinkles. The movement of periwinkles with immature (nontransmissible) infections was less affected by the parasite. During the tidal cycle, infected and uninfected periwinkles differed in both timing and extent of movement. A field experiment confirmed the greater upwards movement of infected periwinkles. The parasite-induced changes in periwinkle behaviour may increase the chances of predation by the final host and could represent an important survival strategy for M. piriformes. Copyright 2000 The Association for the Study of Animal Behaviour.
McCarthy
HO
Applied Biological and Chemical Sciences, University of Ulster
Fitzpatrick
S
Irwin
SW