CHOICE OF MATE, A REPRODUCTIVE ISOLATING MECHANISM BETWEEN SCHISTOSOMA-INTERCALATUM AND SCHISTOSOMA-MANSONI IN MIXED INFECTIONS

In Africa, the two human schistosome parasites, Schistosoma intercalat um and S. mansoni, can be found sympatrically, which poses the problem of the nature of their reproductive isolation. In this paper, experim ental studies of mating behaviour in mixed infections in mice were car ried out. Simultaneous infections without choice of mate showed an abs ence of any physiological barriers preventing encounter and mating of the two species on the same host. Whenever choice was possible, mating did not occur in a random way, but preferentially between partners of the same species (there was a significant prevalence of homospecific pairs). S. mansoni exhibited greater specific mate recognition than S. intercalatum. Moreover, in the absence of S. mansoni female worms, S. mansoni male worms were as competitive as S. intercalatum male worms in pairing with S. intercalatum female worms. It appears from this stu dy that the choice of mate is a reproductive isolating factor between the two species.