POLLEN VIGOR AND THE POTENTIAL FOR SEXUAL SELECTION IN PLANTS

DISCOVERING whether paternal fecundity varies within populations is crucial for evaluating whether male-male competition and/or female choice can lead to sexual selection 1-3. In natural populations of plants, pollinators often deposit mixtures of 'surplus' pollen from several individuals onto receptive stigmas 4-7. Therefore within-flower competition among pollen-tubes for ovules could lead to nonrandom paternal success. We found that pollen competition was common in populations of wild rose mallow (Hibiscus moscheutos). Co-occurring individuals often differed in mean pollen-tube growth rates, and this trait was correlated with the number of seeds the plants sired when pollen mixtures were applied to stigmas. Differences between pairs of individuals in pollen-tube growth rates were consistent across maternal plants, suggesting that sexual selection can occur. This unexpected variation in pollen vigour could lead to nonrandom fertilization whenever pollen-tubes compete for access to ovules.