Parasite infection and the movement of the aquatic snail Potamopyrgus antipodarum along a depth cline

Parasite species that use two or more host species during their life cycle depend on successful transmission between these species. These successive host species may have different habitat requirements; for example, one host species can be aquatic while the other is terrestrial. To overcome this complicating factor in transmission, a wide diversity of parasite species have adaptations that alter habitat preference in one host species in order to facilitate transmission to the next host species.
Two common trematode parasites from New Zealand, Atriophallophorus winterbourni and Notocotylus spp., both have a two-host life‑cycle. The aquatic snail Potamopyrgus antipodarum is the intermediate host, from which the parasites require transmission to dabbling ducks or other waterfowl. Of these parasites, A. winterbourni is most frequently found in snails from the shallow-water margin, which may indicate parasite-induced movement of infected snails to the foraging habitat of dabbling ducks.
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