HIGH-LEVELS OF GENE FLOW IN BUR OAK REVEALED BY PATERNITY ANALYSIS USING MICROSATELLITES

Microsatellite analysis was used to characterize pollen dispersal in a stand of 62 adult bur oaks (Quercus macrocarpa) in northern Illinois. Using POP amplification of four dinucleotide microsatellite loci, pol len donors of 282 acorns collected from three adult trees located in d ifferent parts of the stand were determined by exclusion. Overall at l east 57% of the scorns were pollinated by trees outside of the stand, because all adult trees in the stand were excluded from paternity, Ave rage pollination distance for within-stand pollinations was 75 m, and pollen donors for two of the three maternal trees were randomly disper sed throughout the stand. These two trees also received more pollen fr om 50 m away than from near neighbors, Self-pollination was rare or no nexistent, This study provides direct evidence for high levels of long -distance pollination in a wind-pollinated species, and contradicts tr aditional models of wind pollination which suggest that clouds of poll en dissipate from the source to ineffectively low densities over short distances. Instead, the mating system of bur oak seems to be extraord inarily efficient at producing highly outbred individuals and ensuring long-range pollen flow, perhaps through pollen competition or mate ch oice favoring distant pollen sources.