EFFECTS OF PRE-DISPERSAL SELECTION ON OFFSPRING GROWTH AND SURVIVAL IN ERYTHRONIUM-GRANDIFLORUM

Effects of pre-seed-dispersal processes on offspring vigor were examin ed in Erythronium grandiflorum using manipulations of the number of po llen donors contributing to the pollen pool and comparisons of means a nd variances in offspring growth measurements. There were no effects o f the number of donors on measures of pollen-tube growth, ovule aborti on, seed set, mean seed weight, or seedling germination. Seeds from po llinations 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 do nors. Patterns of within- and among-family variance estimates for the different treatments were consistent with the hypothesis that less-vig orous offspring were eliminated prior to seed dispersal in the multipl e-donor treatments. The difference in the growth of offspring from dif ferent 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 ab ortion of less-vigorous progeny, perhaps as a consequence of early-act ing inbreeding depression, is responsible for the increase in the aver age vigor of offspring from multiply-sired fruits.