Resolution of male-female conflict in an hermaphroditic flower

Abstract

The £owers of most angiosperm species are hermaphroditic. Spatial separation of male and female organs within a £ower (hercogamy) is a common character traditionally interpreted as an adaptation to reduce intra£oral self-fertilization, one potential cost of hermaphroditism. Another possible cost that may lead to selection for hercogamy is physical interference between male and female £oral functions. Here, I present evidence demonstrating the role of a £oral character in reducing female interference with male function. The bi-lobed stigma of the bush monkey£ower closes after receiving pollen, causing increased spatial separation of the anthers and stigma (`movement' hercogamy). Experimental manipulations show that £owers with closed stigmas export more than twice as much pollen to other £owers as those in which the stigma is prevented from closing. However, stigma closure only minimally reduces the potential for intra£oral self-pollination. This study provides the ¢rst experimental evidence that selection to reduce intra£oral male^female interference can be a strong selective force and can drive the evolution of £oral characters usually interpreted as mechanisms to reduce self-fertilization.

Effect of variation in herkogamy on outcrossing within a population of Gilia achilleifolia

“…In such self-incompatible plants, herkogamy may have evolved solely to prevent the interference between the two functions of a perfect flower: pollen export from anthers (male function) and pollen import to the stigma (female function). For example, the stigma may interfere with pollen export if pollen from the anther lands on the stigma instead of on the pollinator owing to close proximity of anther and stigma (Fetscher, 2001). Likewise, anthers may interfere with pollen importation if self pollen clogs the stigma (Galen et al, 1989;Waser and Price, 1991), or if the anthers tightly surround the stigma and physically block pollinator access to the stigma.…”

Recurrent modification of floral morphology in heterantherous Solanum reveals a parallel shift in reproductive strategy

“…The relative position of male and female organs within a flower affects pollen placement and receipt from the pollinator's body, which in turn influences the rates of pollen transfer between plants [14 -16]. In addition, the degree of spatial separation between anthers and stigma within a flower (herkogamy) can reduce sexual interference in self-compatible species [9,17,18] and is functionally related to the extent of within-flower self-pollen deposition, with reduced herkogamy resulting in higher rates of selfing [19,20]. It is therefore expected that changes in flower morphology have the potential to change patterns of pollen transfer, including the relative contribution of self-versus cross-fertilization to offspring production (mating system).…”

“…Correlations between form and function have been demonstrated in many instances including changes in pollinator fauna in closely related species with different floral characteristics (e.g. Aquilegia [3], Mimulus [4], Penstemon [5], Stylidium [6]), visitation by specialized pollinators [7][8][9] and evolutionary shifts from cross-to self-fertilization [10][11][12][13]. Studying the evolution of floral form provides clues about the functional significance of the variation of plants' sexual reproductive structures.…”

Seasonal change in a pollinator community and the maintenance of style length variation in Mertensia fusiformis (Boraginaceae)

“…pollen export), rather than selection to maximize pollen receipt, a possibility we did not consider here. For example, in Mimulus aurantiacus, the large, bilobed stigma closes shortly after receiving pollen -apparently a behaviour that has evolved to minimize interference between male and female functions (Fetscher, 2001). One could imagine that short styles might similarly facilitate pollen export in M. fusiformis (cf.…”