Selfing and outcrossing in a parasitic hermaphrodite helminth (Trematoda, Echinostomatidae)

Abstract

Echinostomes are simultaneous hermaphrodite trematodes, parasitizing the intestine of vertebrates. They are able to self- and cross-inseminate. Using electrophoretic markers specific for three geographical isolates (strains) of Echinostoma caproni, we studied the outcrossing rate from a 'progeny-array analysis' by comparing the mother genotype with those of its progeny. In a simultaneous infection of a single mouse with two individuals of two different strains, each individual exhibits an unrestricted mating pattern involving both self- and cross-fertilization. The association in mice of two adults of the same strain and one adult of another strain shows a marked mate preference between individuals of the same isolate. From mice coinfected with one parent of the three isolates, each parent was shown to be capable of giving and receiving sperm to and from at least two different partners. Mating system polymorphism in our parasitic model is thus discussed in the context of the theories usually advanced.