The combined effect of isolation and Fasciola hepatica infection on the life history traits of Fossaria cubensis

Life history traits of Fossaria cubensis were compared between isolated and paired snails after infection with three miracidia of Fasciola hepatica. F our experimental groups were tested: isolated-unexposed, paired-unexposed, isolated-infected, and paired-infected. A repeated-measures ANOVA showed st atistically significant interactions among isolation, infection, and age ef fects for shell size, number of egg masses per snail, number of eggs per sn ail, and number of viable eggs per snail. Isolated-unexposed snails exhibit ed the higher values of these variables and those of survival and finite an d intrinsic rates of natural increase. Infection stimulated shell growth du ring the prepatent period, but differences were present only in paired snai ls since isolation causes a similar effect. Reproduction, in terms of the n umber of egg masses per snail and the number of eggs per mass per snail, de creases in the presence of parasitic infection, whereas isolation stimulate s it. These effects were observed from early stages of infection. (C) 2001 Academic Press.