| Abstract: | Effects of pre-seed-dispersal processes on offspring vigor were examined in Erythronium grandiflorum using manipulations of the number of pollen donors contributing to the pollen pool and comparisons of means and variances in offspring growth measurements. There were no effects of the number of donors on measures of pollen-tube growth, ovule abortion, seed set, mean seed weight, or seedling germination. Seeds from pollinations with only one donor produced corms that averaged 5% lighter after one season of growth and had lower overall survival after three years compared to corms from pollinations with either three or ten donors. Patterns of within- and among-family variance estimates for the different treatments were consistent with the hypothesis that less-vigorous offspring were eliminated prior to seed dispersal in the multiple-donor treatments. The difference in the growth of offspring from different treatments was apparently not due to pollen competition because pre-zygotic attrition of pollen tubes led to incomplete fertilization of ovules. Results from this study suggest that post-fertilization abortion of less-vigorous progeny, perhaps as a consequence of early-acting inbreeding depression, is responsible for the increase in the average vigor of offspring from multiply-sired fruits. |
