Changes of mate occur in Schistosoma mansoni

Male and female schistosomes are generally assumed to form stable monogamou s pairs for the whole span of their long existence in the mammalian host. R ecent evidence from mixed infections has shown that Schistosoma mansoni mal es can displace S. intercalatum males from their homologous partners, but n o information exists about the existence of similar phenomena within a sing le schistosome species. Here, we determine whether male S. mansoni can disp lace males of the same species from pre-formed pairs in vivo. The availabil ity of clear-cut genetic markers of drug resistance in schistosomes was exp loited to show that hycanthone sensitive S. mansoni males can displace homo specific hycanthone resistant males from pre-formed pairs and vice versa. T he frequency of changes is dependent on the magnitude of the excess single males competing with paired worms. The possible mechanics and the biologica l significance of mate changing are discussed.