Effects of pollen load size and composition on pollen donor performance inwild radish, Raphanus sativus (Brassicaceae)

A critical concern in the debate over the importance of sexual selection in plants is whether the nonrandom mating demonstrable in greenhouse crosses can occur in the field. Field populations likely experience smaller and mor e variable pollen load sizes than those that have been used in many greenho use experiments. Therefore, we performed a greenhouse experiment in which w e varied both pollen load size and composition in wild radish, Raphanus sat ivus, and examined the paternity of seeds. We used five maternal plants and four pairs of pollen donors. We were able to produce pollen loads of 40, 1 18, and 258 grains per stigma. The smallest of the pollen loads was scant e nough to result in a slight, but significant reduction in seed number per f ruit. While variation in pollen load composition significantly affected the proportions of seeds fathered by different donors, variation in pollen loa d size did nor. The relative performance of different donors was constant a cross pollen load sizes, suggesting that, for this species, differential pe rformance of pollen donors can occur at pollen load sizes that are likely t o occur in field populations.