Intergeneric reproductive stimulation and parthenogenesis inSchistosoma mansoni

Abstract

SummaryWhen mice were infected with female cercariae ofSchistosoma mansoniand male cercariae ofSchistosomatium douthitti, many mixed pairs formed. The paired females were approximately the same size as those in unisexual infections, far smaller than females paired withS. mansonimales. Although theSch. douthittimales possessed well-developed testes, sperm were not found in their female partners, which developed scanty vitelline glands and produced laterally spined eggs typical ofS. mansoni. Such eggs yielded swimming miracidia infective to the snail host ofS. mansoni, Biomphalaria glabrata, but not to the lymnaeid snail host ofSch. douthitti. Sporocysts arising from these miracidia were haploid and produced cercariae infective to mice. Parthenogenetically derived female cercariae in mice co-infected with either parthenogenetically derived male or normal diploid maleS. mansonideveloped to large adults of normal appearance, whose eggs yielded diploid miracidia and subsequent generations of normal diploid schistosomes. Parthenogenetically derived females co-infected withSch. douthittimales also paired and produced some eggs containing viable miracidia, which gave rise once again to haploid sporocysts. These observations confirm previous suggestions that the stimulus for maturation in femaleS. mansoniis distinct from that for growth, and is independent of insemination and fertilization. It is concluded that both diploid and haploidS. mansonifemales are capable either of parthenogenesis or of bisexual reproduction when appropriately stimulated.