How does secondary pollen presentation affect the fitness of Polygala vayredae (Polygalaceae)?

Secondary pollen presentation is the relocation and presentation of pollen in floral structures (termed pollen presenters) other than the anthers. These pollen presenters are often found close to the stigma and have been hypothesized to increase the accuracy of pollen transfer, although no experimental studies have been done. We examined the function of the pollen presenter and its efficiency in pollen dispersal, female fitness, and the degree of interference created by self-pollen in the shrublet Polygala vayredae, an insect-pollinated species with secondary pollen presentation. Herkogamy, a mechanism generally involved in the reduction of self-interference, was also evaluated. Significant pollen was lost (49% of total pollen) during the secondary relocation in the pollen presenter. However, pollen was exported from the pollen presenter, and subsequent pollen losses were similar to those in species with primary pollen presentation. Despite the presence of a self-incompatibility system, the numbers of developed pollen tubes as well as fruit and seed production were significantly reduced by the self-pollen interference created at the stigmatic papillae level. The extent of herkogamy correlated positively with female fitness. The secondary pollen presentation mechanism may in fact be an accurate system for pollen transport, but it may also have its costs. Further comparative studies involving species with primary and secondary pollen presentation are needed to fully understand the advantages and disadvantages of secondary pollen presentation.