Pollination by Deceit in a Neotropical Monoecious Herb, Begonia involucrata

Abstract

In the predominantly monoecious genus Begonia, pollen is the only floral reward to pollinators. To investigate the hypothesis that female Begonia flowers attract pollinators by mimicking male flowers, we studied floral display and pollinator behavior in a population of the protandrous perennial herb Begonia involucrata at Monteverde, Costa Rica. The stigmas of the female flowers are bicornute and dark yellow, strongly resembling the anthers of male flowers. The petaloid sepals of male flowers are somewhat larger than those of female flowers, but the number of open flowers does not differ between male- and female-phase inflorescences. Both male and female inflorescences have a sweet odor. Trigona grandipennis, the most frequent flower visitor in the study population, consistently showed a strong preference for male-phase inflorescences; on average, individual male inflorescences received 3.4-9.6 (median 7.2) times as many visits as female inflorescences during five different observation periods. Moreover, visits to male flowers lasted about ten times longer than visits to female flowers (mean 29.8 versus 2.6 seconds). Although visits to female flowers were infrequent and brief, fruit set averaged 76 percent and seed set 57 percent. A hand-pollination experiment indicated that seed set was pollen limited (1.4 times higher after supplemental pollination), but that fruit set was not. Taken together, the striking similarity in male and female flower display, the selective pollinator behavior, and the relatively high levels of fruit and seed set support the hypothesis that the rewardless female flowers of B. involucrata mimic male flowers and are pollinated by deceit.