FACTORS INFLUENCING MALE MATING SUCCESS IN BUR OAK, QUERCUS-MACROCARPA

Pollen donors of acorns and saplings in a stand of bur oak were identi fied by paternity exclusion using microsatellite genotype analysis. He re we examine the influence of several factors likely to affect reprod uctive success of males with wind-dispersed pollen, including distance of pollen donor from maternal tree, genetic relatedness of pollen don or to maternal tree, direction of pollen donor relative to maternal tr ee, and size of pollen donor (crown volume and trunk diameter). Surpri singly, none of these factors were strongly correlated with fertilizat ion success, although weak but significant correlations with crown vol ume and distance were found. The slight influence of distance is actua lly overestimated here, because our analysis necessarily excluded a la rge proportion of pollinations that were effected by trees outside the stand. The pollen donors outside the stand were not identified, but w ere more than 150 meters away. Pollination patterns in this stand of b ur oak are quite complicated. Seed parents were fertilized by multiple pollen donors within the stand from all directions and as far as 200 m away. These results caution against the use of models of pollination that are based on simple distance or directional parameters because t hey will not adequately predict gene flow or male reproductive success . Our results further emphasize the importance of genetically identify ing successful pollen donors rather than relying on patterns of physic al movement of pollen.