Male Reproductive Success and Variation in Fruit and Seed Set in Aquilegia Caerulea (Ranunculaceae)

Abstract

The timing of fruit initiation and the proximity of fruits to resources influence the probability of fruit and seed initiation in many hermaphroditic plants. In two populations of Aquilegia caerulea, both fruit and seed set decreased significanlty between early and late flowers. Low fruit and seed set of late flowers was not due to pollen limitation. Fruit and seed set of late flowers remained low when extra pollen was added to these flowers (pollen quantity), or when all flowers on an inflorescence received self or outcross pollen (pollen quality). While competition for resources occurred among flowers, resource limitation was not responsible for the low fruit and seed set of late flowers. Indeed, preventing pollination of late flowers significantly increased both fruit and seed set of early flowers, but fruit and seed set of late flowers remained low when early flowers were prevented from setting fruits. Late flowers were not just smaller or larger replicates of early flowers, as they allocated more reproductive resources to male function relative to early flowers. Neither herbivory nor architectural constraints could explain the low fruit and seed set of late flowers. While previously published adaptive explanations proposed to explain the low fruit and seed set of late flowers have emphasized a positive aspect to female reproductive success, it is suggested here that both male and female functions should be considered. Morphological data and estimates of male and female reproductive success demonstrate how, both morphologically and functionally, late flowers on inflorescences of A. caerulea specialize as males, early flowers as females. It will be argued that potandry in this sequential bloomer is expected to select for an increase in relative male allocation between early and late flowers, and that the observed pattern of resource allocation and the decrease in fruit and seed set between early and later flowers is consistent with this prediction.