Abstract: Through its role in regulating pollinator behavior, floral display size and nectar gradient within inflorescences may alter the extent of geitonogamy and thus female reproductive success in protandrous species. However, this has seldom been examined. By quantifying selfing rate, seed number and male donor number, we estimated the effects of floral display size, nectar gradient and their interactions on plant reproduction in protandrous Aconitum gymnandrum. At plant level, selfing rate and seed number increased with a larger floral display of both main and lateral inflorescences but reduced with a declining nectar gradient. The effects of floral display of the main inflorescence on selfing rate and seed number were altered by the nectar gradient and floral display of lateral inflorescences as shown by their interactions. Larger floral display of the main inflorescence reduced male donor diversity. At flower level, the selfing rate and the seed number varied among flower positions, in which bottom flowers had lower selfing rate and higher seed number than top flowers. The effects of floral traits on geitonogamous selfing rate and seed number were inconsistent among flower positions. Although low cost of geitonogamous selfing for reproduction was tested by hand-pollination, the selfing rate was negatively correlated with seed number and male donor number in open-pollinated population. Our results suggest the potential role of trade-off between geitonogamy cost and reproductive benefit in evolution of floral traits. The variation of selfing rate and reproductive success among flowers may alter the trade-off and thus complicate evolution of traits.

Key words: geitonogamy, protandry, nectar gradient, floral display, seed quantity, male donor number, Aconitum gymnandrum