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

Abstract

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.

Consequences of nectar robbing for the fitness of a threatened plant species

“…Nectar is produced at the base of the corolla (daily nectar production: 1.9 ± 0.86 ll with 16.0 ± 6.23% of sugar), and flowers are able to resynthesize after several removals (Castro et al 2008b). Furthermore, flowers possess a mechanism of secondary pollen presentation, where the pollen is presented to the pollinators in a specialized region of the stigma (the pollen presenter; Castro et al 2008c). Fruiting occurs in late spring (May-June) with the production of a dehiscent capsule (10.0 ± 1.04 mm long and 8.8 ± 0.79 mm wide) containing two seeds (4.7 ± 0.24 mm long, each weighting 9.1 ± 1.62 mg, dry weight) (Castro 2007).…”

Pollen packaging and dispensing: adaption of patterns of anther dehiscence and flowering traits to pollination in three Epimedium species

“…; Harder & Wilson ; Castro et al . ), anther appendages (Han et al . ) and anther arrangement (Harder & Barrett ; Kudo ).…”

A treatment for Polygala of northern Australia

“…Indirect evidence for both selfpollination and herkogamy (a mechanism generally involved in the prevention of self-interference) exist for Polygala. However, Castro et al (2008) found that stigma interference did appear to influence pollen-tube growth in some herkogamous species, and so few generalisations can be made. Group 2, entirely Australian endemics, comprises species with very broad (P. exsquarrosa) and narrow (P. canaliculata) distributions; members have intricate and specific style and/or stigma arrangements characterised by the presence of the second sterile stigma, suggesting unique pollen presentation and, therefore, potentially unique pollinators.…”

“…Westerkamp and Weber (1997b). There are some species in the genus that have two fertile stigmas (Castro et al 2008). This is considered the ancestral form, and in some species one of the ancestral stigmas has been modified to form a pollen presenter or has been lost altogether, as is the case for many Australian species (Ladd and Donaldson 1993;Ladd 1994;Castro et al 2008).…”