LAUSR

PREMISE OF THE STUDY Pollinator sharing of co-flowering plants may result in interspecific pollen receipt with a fitness cost. However, the underlying factors determining the effects of heterospecific pollen (HP) are not fully understood. Moreover, the cost of stigma closure induced by HP may be more severe for plants with special touch-sensitive stigma than for plants with non-touch-sensitive stigma. Very few studies have assessed HP effects on stigma behavior. METHODS We conducted hand-pollination experiments with ten HP donors to estimate HP effects on stigma behavior and stigmatic pollen germination in Campsis radicans (Bignoniaceae) at low and high pollen loads. We assessed the role of phylogenetic distance between donor and recipient, pollen size, and pollen aperture number in mediating HP effects. Additionally, we observed pollen-tube growth to determine the conspecific pollen-tube growth advantage. RESULTS Stigma behavior differed significantly with HP of different species. Pollen load increased, while pollen size decreased the percentage of permanent closure and stigmatic germination of HP. Stigmatic HP germination increased with increasing aperture number. However, HP effects did not depend on phylogenetic distance. In addition, conspecific pollen had a pollen-tube growth advantage over HP. CONCLUSIONS Our results provide a good basis for understanding the stigma-pollen recognition process of plant taxa with touch-sensitive stigmas. We concluded that certain flowering traits drive the HP effects on post-pollination period. To better understand the impact of pollinator sharing and interspecific pollen transfer on plant evolution, we highlight the importance of evaluating more factors determining HP effects at the community level. This article is protected by copyright. All rights reserved.