Mating Behavior and Development of Schistosomes in the Mouse

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Abstract
Attempts were made to reveal the operation of pheromones acting first to bring the opposite sexes of Schistosoma mansoni together for mating and second to induce and maintain the sexual and somatic maturity of the mated females. Mice with unisexual infections were quick-frozen in liquid nitrogen and dissected after partial thawing in order to examine the distribution of the worms in the portal system while preventing the postmortem migrations which may occur in ether-killed mice. More than 97% of some 800 worms found in 35 mice were located within the liver or close to it in the portal vein. Mixed infections in mice with one or both sexes of S. mansoni, Schistosomatium douthitti and/or Heterobilharzia americana revealed almost random mating during the early stages of the mating process. These observations imply that in the mouse host, mating noting occurs by trial and error after the two sexes rendezvous in the liver. Homosexual pairing of males further suggested that the pairings resulted from thigmotaxis rather than chemotaxis. Mice infected with normal and X-irradiated S. mansoni cercariae of both sexes yielded nearly normal females mated with sterile males, and small, sexually mature females mated with stunted males. S. mansoni females, cross-mated with S. douthitti or H. americana males, reached sexual maturity and produced a few viable eggs, but did not grow larger than unmated females. It appears, therefore, that body growth more than sexual maturation depends on conspecif ic mating. The findings suggest that a pheromone is produced by the male which is essential for the initiation and maintenance of the female partner''s maturation, and which may inhibit the development of homosexually embraced males.