Omphiscola glabra (Gastropoda, Lymnaeidae): Changes occurring in natural infections with Fasciola hepatica and Paramphistomum daubneyi when this snail species is introduced into new areas

Cross-transplantations of Omphiscola glabra between two French departments (Haute-Vienne and Indre) were carried out to study snail settlement in these new sites during six years and to determine if this snail species was well adapted to its local parasites (Fasciola hepatica and Paramphistomum daubneyi). Local snails placed in new sites for each department were used as controls. In Indre furrows, the number of adults per population and the area of each habitat peaked on the third year post-introduction. Similar findings were also noted in the Haute-Vienne furrows occupied by local snails but peaks were only observed on the fourth year. In contrast, in Haute-Vienne sites populated by introduced snails, there was a progressive decrease in snail abundance and habitat area from the second year. The local O. glabra transplanted in Haute- Vienne kept their same degree de susceptibility to F. hepatica and P. daubneyi, thus demonstrating a good adaptation of these snails to their parasites. In other groups of transplanted snails, the first natural infections were only noted from the second or third year post-introduction and their prevalence progressively increased over time. Local adaptation of these latter snails to parasites would be more progressive in time and would stretch over several snail generations.