INFLUENCES OF FLORAL VARIATION ON POLLEN REMOVAL AND SEED PRODUCTION IN WILD RADISH

Studied the effects of corolla size, pollen production, and pollinator visitation frequency on pollen removal (an estimate of male reproductive success) and pollen deposition and seed production (female success) in Raphanus sativus. For flowers receiving a single honey bee visit, corolla size was positively correlated with pollen removal, but not with pollen deposition on stigmas or seed production. Flowers receiving an average of 3.7 honey bee visits (in 1987) also showed a correlation between corolla size and pollen removal. When flowers were visited an average c5.7 times by honey bees (1988) there was no significant relationship between corolla size and either pollen removal or estimates of female reproductive success (pollen deposition on stigmas and seed production). Honey bees demonstrated a preference for large flowers, either by significantly overvisiting large flowers or by visiting the large flowers before visiting smaller flowers. Most radish flowers receive numerous visits, but even with frequent visitation, at least 20% of the pollen a flower produced was not removed. Flowers with greater pollen production had a larger proportion of pollen removed. Pollen removal was a positive decelerating function of honey bee visitation frequency. Number of pollen grains removed per visit declined with increasing honey bee visits. The male fitness function (pollen removal plotted against pollen production) was positive and decelerating in 2 experiments; positive and linear in one study. Large flowers may have greater male success than small flowers by virtue of their greater pollen production, their greater pollinator visitation frequency, and their earlier pollinator visitation. -from Authors