The Basis of Pollinator Discrimination Between Male and Female Phase Flowers in Impatiens capensis and the Implications for Plant Mating Systems
author: Robin Russell
advisor: Keith Karoly
ABSTRACT: Pollinators can discriminate visually between floral sex morphs based on the presence or absence of sex characters, such as anthers, which may indicate an expected reward. This discrimination may prevent the evolution of dioecy by decreasing the reproductive success of male sterile mutants in hermaphroditic populations. The basis of discrimination between sex morphs in the hermaphroditic species Impatiens capensis was investigated. To determine pollinator preferences in this species, pollinator visitation rates to naturally occurring male (with anthers) and female (without anthers) phase flowers were observed. Anthers were removed from natural male phase flowers to observe whether pollinators discriminated on the presence or absence of anthers. Pollinator foraging behavior was observed to determine the sequence and number of naturally occurring male and female phase flower visitations. Based on these observations pollinators do discriminate between the natural male and female phase flowers. However, the observation of pollinator visitation rates to emasculated flowers of Impatiens capensis, indicate that the presence or absence of anthers is not the basis of discrimination in this species. Pollinator discrimination between male and female morphologies is not unique to Impatiens capensis. Twenty-five studies involving pollinator behavior on male, and female morphologies of flowers were reviewed. In twenty-three of the studies pollinators were observed discriminating between morphs. Fifteen studies noted that pollinators preferred male morphologies to female morphologies, but the basis of discrimination was often unclear.