CHANGE OF MATE AND MATING COMPETITION BETWEEN MALES OF SCHISTOSOMA-INTERCALATUM AND SCHISTOSOMA-MANSONI

Previous studies on mating behaviour of Schistosoma intercalatum and S . mansoni, two human schistosomes which may overlap in parts of Africa , have shown that in mixed infections in mice there are no physiologic al barriers preventing heterospecific pairings. However, when choice i s possible, matings occur preferentially between partners of the same species. In this paper, further experimental studies on mating behavio ur of the two species were conducted. Sequential infections showed tha t heterospecific pairs of worms change partners to homospecific pairs when given the opportunity. The change of mate is a progressive proces s requiring up to, at least 8 weeks, and this phenomenon is due to the male worm seeking the appropriate female. S. mansoni males are better at pairing with females than S. intercalcatum males, and they will ch ange partner to pair with homologous females in preference to heterolo gous females whenever given the opportunity. Moreover, in the absence of S. mansoni female worms, unpaired S. mansoni male worms pull away f emale S. intercalatum from male S. intercalatum. It appears from this study that S. mansoni males are much more competitive than S. intercal atum males at pairing with females, and this is a disadvantage for S. intercalatum in situations of sympatry.