In the many species in which breeding between close kin yields deleterious effects (inbreeding depression), outbreeding is promoted by various mechanisms, such as kin recognition and, in hermaphrodites, barriers to self-fertilization. When the cost of inbreeding is not too high, hermaphrodites will be selected to self. The sexually reproducing, simultaneous hermaphroditic flatworm Dugesia polychroa does not self-fertilize, suggesting that selfing is too costly in this species. To ascertain whether kin recognition exists as a behavioral mechanism to avoid inbreeding in D. polychroa, experiments were designed using two genetically identical regenerates, or clonemates, from a single halved worm. The mating behavior of clonemates vs. unrelated worms was recorded, in pairs and in triads consisting of two clonemates and one unrelated worm. No clear differences in frequency or duration of copulations could be demonstrated between clonemates or unrelated worms, either in pairs or triads. Our results indicate that there is no kin recognition mechanism or selective mating for inbreeding avoidance in D. polychroa. We hypothesize that, in the field, dispersal in this species is sufficient to limit inbreeding.
- Mate choice