Secondary pollen presentation on anther hairs enhances reproductive fitness in Brandisia hancei, a protogynous perennial with autonomous selfing

Background: Secondary pollen presentation (SPP) is a phenomenon where pollen is relocated from within the anthers to other floral structures for presentation.Aims: We report a new mechanism of androecial SPP on anther hairs, which is involved in increasing reproductive fitness in Brandisia hancei.Methods: The morphological change of anther hairs during floral ageing was recorded, and pollen grains were quantified after anther hair removal to clarify the roles played by hairs in pollen retention. Additionally, fruit set and seed set were assessed to investigate the efficiency of anther hairs to reproductive success.Results: Young flowers of B. hancei showed approach herkogamy, while autonomous selfing was achieved by changes in relative positions of the stigma and anthers during floral ageing. In B. hancei, anthers developed characteristic hairs of epidermal origin, and hairs originated along the furrow between the paired pollen sacs and were used for SPP after anther dehiscence. Anther hairs increased pollen retention by over 70% in later floral-age stages, and seed set decreased by about 30% after anther hairs had been removed.Conclusions: In the process of autonomous selfing, SPP on anther hairs enhances both the male and female functions of the flowers of B. hancei.