Temporal variation in parasite loading in relation to life history patterns of Littorina obtusata and L. fabalis

Abstract

Parasitic infection of Littorina obtusata (L.) and Littorina fabalis Turton by larval digeneans was studied in summer (August) and winter (February) on a sheltered shore at St Michael's Island, Isle of Man. Sampling was timed to investigate parasite loading at different stages of the littorinids' life history. Nine species of digeneans were identified and infection rates were similar between the species, with a slightly higher prevalence in females for L. obtusata and males in L. fabalis. Temporal differences in infection were small, although metacercariae and degenerate infections were greater in female L. obtusata in February. Analysis of shell parameters and size of the penis in males and the palliai oviduct in females revealed morphological differences between parasitised and uninfected individuals. Parasitic stunting of the penis was evident in both species and the palliai oviduct was also smaller in parasitised females. There was also a tendency for parasitised individuals to have larger shells; although size also varied with season for L. fabalis. © 1998 Kluwer Academic Publishers.