Differential siring success of PGI genotypes in Clarkia unguiculata (Onagraceae)

Competition among pollen grains fur the fertilization of ovules can play an important role in determining the male and female reproductive success of flowering plants. To examine the influence of pollen-donor genotype on mole reproductive success, hand-pollinations were conducted on Clarkia unguicul ata and the siring success of pollen-donor plants was compared between dono rs homozygous for different allelomorphs of the allozyme PGI (phosphoglucoi somerase). Donors homozygous for the B allele sired more seeds than C-allel e donors. Single-donor crosses indicated that C-donor-sired seeds ore abort ed more often than are B-donor-sired seeds, suggesting that the B-allele do nor's advantage in mixed pollinations was a result of differential abortion . A negative relationship between pollen load and the siting success of B-a llele donors implies that pollen from B-allele donors has reduced performan ce relative to C-allele donors when pollen loads are high. These data demon strate consistent differences in siring success between individuals homozyg ous for different alleles at a single locus and suggest that variation at t he Pgi locus map be maintained by a post-pollination trade-off.