Paternal Success Following Mixed Pollinations of Campsis radicans

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Abstract
I examined the relative success of pollen donors in siring viable seeds following mixed (two-donor) hand pollinations of the woody climber, Campsis radicans,. Paternity was assigned using an electrophoretic marker. When pollen from two donor plants was mixed and applied to stigmas, the numbers of viable seeds sired by the two donors were generally unequal. The relative success of the two donors in a mixture was correlated with the relative success of the two donors when their pollen was applied in single-donor loads to different stigmas on the same plant. However, performances of two donors were generally more equal when their pollen was applied in mixed loads than when applied in single-donor loads. While single-donor pollinations are often used to assess donor performance in studies of plant paternity, the above results suggest caution in extrapolating from success in single-donor pollinations to success in nature, where mixed pollinations are probably the rule. When ratios of pollen from two donors in a mixture changed, the success of the two donors changed roughly in proportion. Thus there is no basis for challenging the frequent assumption in gender allocation models that changes in pollen production produce proportional changes in male success. Relative performance of pollen in a mixture was unaffected by the total number of pollen grains deposited. Several lines of evidence suggest that postzygotic phenomena (e.g., seed abortion) are important in determining the success of different pollen donors in Campsis.