LAUSR

PREMISE Those co-flowering species that have not evolved an avoidance mechanism may exhibit tolerance to heterospecific pollen (HP) deposition as an adaptive strategy to minimize any deleterious effects of HP transfer, but empirical evidence for the tolerance hypothesis remains scarce. METHODS To estimate the potential effects of heterospecific pollen deposition (HPD) on female reproductive success, we counted conspecific (CP) and HP pollen grains deposited on stigmas and assessed subsequent seed set of both open- and hand-pollinated flowers in three co-flowering Silene species with exposed stigmas that usually received numerous HP grains on the elongated receptive area. RESULTS HP percent per flower varied from 16.6% to 43.0% among three species. Silene chungtienensis experienced lower HP percent and the CP-HP relationship was neutral, S. gracilicaulis and S. yunnanensis experienced relatively higher HP percent and the CP-HP relationship was positive. Positive effects of CP and HP number on natural seed set were observed in all three species, but stronger negative effects of HP percent in S. chungtienensis and S. gracilicaulis. In hand-pollinated flowers of the three Silene species there was no decrease in seed set with HP whether CP was in excess or insufficient, indicating no negative effects of HPD on seed production. CONCLUSIONS Consistent with the tolerance hypothesis, our results indicated that species experiencing higher HP interference are likely to be tolerant to an increase of HP percent. These species with generalist-pollinated flowers and exposed large stigmas may benefit from an increase of conspecific pollen deposition, despite the associated increase in heterospecific pollen deposition. This article is protected by copyright. All rights reserved.