Sperm trading in a hermaphroditic flatworm: reluctant fathers and sexy mothers

摘要

When matings are frequent and received sperm are digested, hermaphrodites should trade sperm when mating. We investigated sperm trading in the flatworm Schmidtea (Dugesia) polychroa and manipulated mating interests to investigate its possible causes. In 106 mating pairs consisting of nonisolated indiniduals, no sperm donation in either direction (35/100) and reciprocal exchange (38/100) were more common than expected by chance, whereas unilateral transfer (27/100) was less frequent, confirming sperm trading.