The monogenean Gyrodactylus gasterostei and its host, the three-spined stickleback Gasterosteus aculeatus, were employed as a model system to investigate the influence of gyrodactylid maturity on host transfer. Laboratory experiments included the determination of maturity (presence of a male copulatory organ) and reproductive status (presence of a daughter parasite) of the transmitting worms. Parasites with a male copulatory o...