Each coin has two sides: A positive role of alien Potamopyrgus antipodarum (Grey, 1843) snails in reducing the infection of native lymnaeids with trematodes


 The change in the distribution of organisms in freshwater ecosystems due to natural or man-made processes raises the question of the impact of alien species on local communities. Although most studies indicate a negative effect, the positive one is more difficult to discern, especially in multi-species systems, including hosts and parasites. The purpose of the study was to check whether the presence of an alien host, Potamopyrgus antipodarum, reduces the intensity of Echinoparyphium aconiatum metacercariae in a native host, Radix spp. We additionally tested the impact of water temperature and the biomass of alien host on the dilution effect. We experimentally studied i) the lifespan of echinostome cercariae in different temperatures, ii) the infectivity of cercariae towards alien host and native host, and iii) the impact of different biomass of alien host on the intensity of metacercariae in native host. We found that cercarial survival and infectivity were temperature-dependent. However, cercarial survival decreased with increasing temperature, contrary to cercarial infectivity. Echinostome cercariae entered the renal cavity of both the native host and alien host, and successfully transformed into metacercariae. The number of metacercariae in the native host decreased with increasing biomass of the alien host. Our results indicate that lymnaeids may benefit from co-occurrence with P. antipodarum, as the presence of additional hosts of different origins may reduce the prevalence of parasites in native communities. However, the scale of the dilution effect depends not only on the increased spectrum of susceptible hosts but also on the other variables of the environment, including water temperature and host density.