The extent to which the genetic structure of populations of forest herbs controls their reproductive success is not well understood. We used comparisons of naturally and hand-pollinated flowers in northern Ohio populations of mayapple, Podophyllum peltatum, to determine the extent to which genetic variation at the population level may influence fruit and seed production. Mayapple populations were located at 4 wooded sites in the Cleveland Metroparks where 125 patches with at least 7 flowering stems per patch were marked. Flowers in 31 patches were hand-pollinated using pollen from other patches or pollen from other flowers in the same patch. The rest of the flowers were exposed to natural pollination. Developing fruits, were measured every 7-10 days for a month, then collected and dissected to determine seed number.
Results/Conclusions
Natural fruit production varied from 2.7 to 37.9% across sites. The site with the lowest natural fruit production also had a relatively low rate of fruit production among flowers that were hand-pollinated between patches (38% vs. 85.7%). The rate of fruit production among flowers pollinated within patches was generally low (<15%) across all sites. Regression analysis using data from the site with the lowest natural fruit set showed a positive relationship between the number of seeds per fruit from intra-patch crosses and the distance between donor and recipient flowers (F = 8.00; df = 1, 46; p = .007). A significant relationship was not found at the other site in which intra-patch crosses were done (F = .089, df = 1, 65; p = .77). A positive relationship between seed set and distance between crossed flowers suggests that patches are dominated by a small number of genotypes; the lack of such a relationship suggests greater within-patch genotypic diversity. Therefore, our results indicate that the genetic structure of mayapple populations varies among sites and may contribute to inter-site differences in reproductive success.