Do dichogamy and herkogamy reduce sexual interference in a self-incompatible species

1. Dichogamy and herkogamy respectively represent the temporal and spatial separation of male and female reproductive functions. They are regarded as mechanisms to avoid selfing, to promote outcrossing and, particularly in self-incompatible plants, to reduce sexual interference. However, little is known about the extent to which these mechanisms reduce sexual interference, and whether this reduction impacts fitness. 2. We studied patterns of dichogamy and herkogamy, their influence on sexual interference, and the fitness outcome in self-incompatible Passiflora incarnata. We manipulated flowers to be adichogamous or unisexual to evaluate fruit production under increased and decreased sexual interference. 3. Incomplete protandry guaranteed that almost half of the pollen could be successfully exported without interfering with the stigmas, indicating dichogamy may facilitate male pollination success. We found no difference in pollen deposition between natural and emasculated flowers, suggesting that herkogamy does not decrease self pollination. Increased herkogamy resulted in reduced pollen deposition and lower probability of setting fruits, however, a higher seed number. No difference in female fitness was detected under experimentally increased or decreased sexual interference. 4. Taken together, our results suggest that dichogamy is mostly driven by the advantage to male fitness and herkogamy is chiefly determined by female fitness. The lack of difference in female fitness under varied levels of sexual interference indicates that male function is more likely to play a role in shaping floral traits that reduce sexual interference.