SMITH-HUERTA, NANCY L.* and M. BARBARA NEMETH. Department of Botany, Miami University, Oxford OH, 45056. - Pollen grain deposition, pollen competition, and progeny vigor in a natural population of Clarkia unguiculata (Onagraceae).
When the number of pollen grains deposited on a stigma exceeds ovule
numbers, the potential for competition between individual pollen
grains exists. In natural plant populations, pollen grain deposition
patterns can vary greatly, thus affecting the intensity of pollen
competition for ovules. Intensity of pollen competition can in turn
affect progeny vigor. We examined pollen deposition patterns, the
relationship of pollen deposition to seed set, and the relationship of
pollen competition intensity to seedling vigor in a natural population
of Clarkia unguiculata. Within 6 hours of receptivity, an
average of 61 pollen grains were deposited on stigmas, by 48 hours
this number rose to an average of 148 pollen grains. These numbers
were sufficient for full seed set in this population which averages 49
seeds/capsule. However, flowers exposed to pollinators for only 6
hours set significantly fewer seeds (23 seeds/capsule) than flowers
exposed for 48 hours (35 seeds/capsule), and both treatments set
significantly fewer seeds than the average of 49 seeds/capsule for
this population. All measures of progeny vigor (percent germination,
cotyledon width, and first foliar leaf width) showed no significant
differences between the 6 hour and the 48 hour treatments. Our data
suggest that the intensity of pollen competition in Clarkia
unguiculata affects seed set but does not affect progeny vigor.
Key words: Clarkia unguiculata, competition, deposition, natural population, pollen, progeny vigor