MATING-BEHAVIOR IN MIXED INFECTIONS OF SCHISTOSOMA-HAEMATOBIUM AND SCHISTOSOMA-MATTHEEI

In mixed infections of Schistosoma haematobium and S. mattheei, homosp ecific and heterospecific pairs are formed, with a preponderance of ho mospecific pairs indicating the existence of a mate preference system. S. haematobium apparently exhibits a greater specific mate recognitio n system than does S. mattheei. In sequential infections when mice are exposed to S. mattheei 4 weeks after infection with S. haematobium, S . haematobium males are better at pairing with S. mattheei females tha n are S. mattheei males. Hence, genetic exchanges between S, haematobi um and S, mattheei giving rise to viable hybrids poses the problem of the genetic identity of these species of schistosomes. The most import ant reproductive isolating mechanisms are definitive host specificity, S. haematobium being primarily a parasite of man, whereas S. mattheei is a parasite of domestic stock and wild ungulates, and the preferenc e for homospecific pairings in simultaneous infections. In contrast, w hen S. haematobium is the older infection, S. haematobium males are be tter than S. mattheei males at pairing with females of either species. Hybridisation is the likely outcome of such interactions. The lack of viability of S. mattheei male X S. haematobium female indicates genet ic differences between the two species. Occurrences of natural hybridi sation between S. haematobium and S. mattheei may lead to a change in the response of the parasite to chemotherapeutic treatment.