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An uncommon snail-trematode interaction pattern was found for the Pseudosuccinea columella – Fasciola hepatica model under laboratory conditions. Week-old juveniles from two isolates showed very high rates of infection (90.0% and 93.3%) after exposure to five miracidia. They also showed differences in their life history traits when compared to a control group. However, they did not exhibit the increase in size and reduction/cessation in host fecundity which is usually observed in most of the other related snail-trematode systems. In contrast, infected juvenile P. columellashowed increased egg laying after the onset of cercarial emission and there was no effect on growth. A third isolate of P. columellawas found to be refractory to miracidial infection. This constitutes the first report of non-susceptibility to F. hepaticain a lymnaeid species which is usually susceptible. These non-susceptible snails exhibited lower fecundity and survival compared to non-exposed susceptible snails under identical laboratory conditions. The differences observed in terms of life span and reproduction could result from the cost of resistance for individuals from this isolate.

Life history traits of Fossaria cubensiswere compared between isolated and paired snails after infection with three miracidia of Fasciola hepatica. Four experimental groups were tested: isolated–unexposed, paired–unexposed, isolated–infected, and paired–infected. A repeated-measures ANOVA showed statistically significant interactions among isolation, infection, and age effects for shell size, number of egg masses per snail, number of eggs per snail, and number of viable eggs per snail. Isolated–unexposed snails exhibited the higher values of these variables and those of survival and finite and intrinsic rates of natural increase. Infection stimulated shell growth during the prepatent period, but differences were present only in paired snails since isolation causes a similar effect. Reproduction, in terms of the number of egg masses per snail and the number of eggs per mass per snail, decreases in the presence of parasitic infection, whereas isolation stimulates it. These effects were observed from early stages of infection.