Lack of prezygotic isolation by assortative mating between the two cryptic species of the polytypic Schistosoma intercalatum taxon.

Abstract

Ten mice were individually exposed to 30 male and 30 female cercariae of Schistosoma intercalatum from Cameroon and to 30 male and 30 female cercariae of S. intercalatum from Zaire. Ten weeks later, the nine surviving mice were killed, and a total of 263 adult schistosomes (228 pairs, 7 unpaired males, 28 unpaired females) were perfused. All worms were identified utilising the random amplified polymorphic DNA technique using primer OPG06 which enables the differentiation of the Cameroon and Zaire genotypes. The data demonstrate that there were no significant differences between the number of homospecific pairs observed compared with the expected number under the null hypothesis. Matings occurred in a random manner indicating that mate choice did not exist for the two genotypes of S. intercalatum. Hence there is no prezygotic isolation mechanism which would prevent the interaction of the two genotypes if they were sympatric. However, as they are allopatric, the possibility of the production of unfit hybrids does not arise. Consequently, the reinforcement of a prezygotic isolating mechanism does not play a significant role in the speciation process.