Prior Selfing and Gynomonoecy in Silene Noctiflora L. (caryophyllaceae): Opportunities for Enhanced Outcrossing and Reproductive Assurance

The production of seed by both selfing and outcrossing, or mixed mating, may be selected for under conditions of variable pollinator availability. Seed production was examined following experimental manipulations of perfect and pistillate flowers of the gynomonoecious plant Silene noctiflora. Style excision experiments in a greenhouse demonstrated that autonomous selfing occurs in the perfect flowers prior to their opening and continues as the flower ages; 45% of ovules were fertilized prior to flower opening and 95% by the third night of opening. Field experiments conducted in four populations showed that autonomous selfing of perfect flowers also occurs in the field. Perfect flowers excluded from pollinators had similar seed set to perfect flowers that were open to pollinators, and emasculated flowers had very low levels of seed set. These results are concordant with the hypothesis that selfing may be selected to confer reproductive assurance when pollinator visitation limits seed set. Pistillate flowers also showed significant pollinator limitation because hand-pollinated pistillate flowers had significantly higher fruit set than those open to pollinators. Pollinator visitation, while low, occurs during both day and night, even though flowers are only fully open at night. The production of perfect flowers capable of autonomous selfing, together with the plastic production of pistillate flowers, confers reproductive assurance and enhances the likelihood of producing outcrossed seed.