THE RELATIVE COSTS OF SELF- AND CROSS-FERTILIZED SEEDS IN IMPATIENS CAPENSIS (BALSAMINACEAE)

By using a generally applicable technique that involves monitoring the development and survivorship of flowers and seed capsules, I estimated the material and energetic costs of producing self- and cross-fertilized seeds in Impatiens capensis. All flowers and fruits on six plants were censused intensively for the two-month period of reproduction. Cleistogamous (selfing) flowers ripened seed in about 24 days, compared to about 36 days for the chasmogamous (outcrossing) flowers. In terms of dry weight, selfed seeds cost about two-thirds as much as outcrossed seeds: 12.4 versus 18.4 mg dry weight per seed. When adjusted to the currency of calories, and including an independent estimate of pollen and nectar production in outcrossing flowers, I estimate the costs to be about 65 and 135 calories per selfed or outcrossed seed. Sources of error include the accuracy of the estimates of flower and fruit weight, and possible differences among the developmental stages in respiratory costs. The cost discrepancy implies that outcrossed seeds should possess a countervailing fitness advantage large enough to offset their greater energetic cost.