SEX DIFFERENTIAL NECTAR SECRETION IN PROTANDROUS ALSTROEMERIA-AUREA (ALSTROEMERIACEAE) - IS PRODUCTION ALTERED BY POLLEN REMOVAL AND RECEIPT

We examined diurnal and nocturnal nectar secretion across sexual stage s in protandrous Alstroemeria aurea, a bumble bee-pollinated herb with long-lived flowers native to the southern Andes. We found the followi ng patterns: (1) most nectar was produced diurnally and (2) three time s more sugar was secreted during the male than female phase, not only because the male phase lasted longer but also because the rate of nect ar production was higher. This 3:1 ratio in nectar production matched the ratio of the minimum number of bumble bee visits required on avera ge to saturate male (pollen removal) vs. female (seed set) functions. Standing crop of nectar, on the other hand, did not differ greatly bet ween male-and female-stage flowers left open to visitors, because the high-production male-phase flowers were visited more frequently than f emale-phase flowers. In an experiment concurrent with the repeated nec tar sampling of individual flowers over their life-span, we removed po llen from anthers or deposited pollen on stigmas by hand. Neither trea tment, designed to mimic effects of visits by Alstroemeria's native bu mble bee pollinator, affected nectar production. The absence of plasti city in nectar secretion in relation to pollination events may reflect a low cost of nectar production, or may result from developmental con straints related to the evolution of the synchronous protandry that ch aracterizes A. aurea.