Reproductive Success and Sex Variation in Nectarless and Rewarding Orchids

Abstract

In hermaphroditic plants, the number of flowers in the inflorescence and the presence of a reward may have a differential effect on male (pollen dissemination) and female (pollen deposition) reproductive success and thus on the evolution of floral features. Two rewarding and one nectarless orchid species were used here to test the hypothesis that a large inflorescence serves primarily to increase male reproductive success (“male function hypothesis”). We have found that both in rewarding and in nectarless species, the rate of increase of male reproductive success with the number of flowers is not significantly different from that of female reproductive success, which does not support the male function hypothesis. Since the lack of reward causes lower reproductive success in nectarless orchids, we hypothesized that in nectarless species, the average time interval between flower opening and its first visit by a pollinator is longer compared with rewarding ones. Our data confirmed this hypothesis.