Parasitism, reproductive assurance and the evolution of reproductive mode in a freshwater snail

Abstract

The Red Queen model for the maintenance of sex suggests that parasites may evolve rapid adaptation to common host genotypes, and thus there would be strong frequency-dependent selection for those rare host genotypes generated through sex. The reproductive assurance hypothesis asserts that parthenogens are favoured under conditions where male gametes are limiting. Here I examine the biogeographic distribution of reproductive mode and parasitism by digenetic trematodes in a freshwater snail, Campeloma decisum. Parthenogenetic populations have higher levels of parasitism, supporting the prediction from the Red Queen hypothesis that parasites evolve to exploit common host genotypes. Although parthenogenesis is more common in glaciated regions, parthenogenesis may assure reproduction in glaciated regions because of severe sperm limitation caused by a digenetic trematode, rather than by colonization advantage.