Slow stamen movement in a perennial herb decreases male-male and male-female interference

Successive stamen movement in Saxifraga candelabrum is responsive to weather and pollinator visits

BACKGROUND

Successive stamen movement is a complex plant behavior involving successive uplift of stamens and pollen release, which plays a role in reducing sexual interference, increasing pollen deposition and promoting pollen export. Although reported from several taxa, studies on whether the movement can be influenced by abiotic and biotic factors are scarce.

METHODS

In this study, we here for the first time described a pattern of successive stamen movement in Saxifraga candelabrum (Saxifragaceae). We then compared the rates of stamen movement in S. candelabrum under different weather and varying pollinator visits. Pollen packaging and presentation schedule of S. candelabrum were also investigated.

RESULTS

The results showed that the number of stamens bent per day in sunny days was significantly higher than overcast and rain. Flowers that receive more pollinator visits (control treatment) had significantly higher number of stamen movement than those that received fewer (removal treatment) and none (bagging treatment). Throughout the staminate phase of a flower, there was a progressive increase in both pollen quantity of individual stamens and pollen presentation during each day.

CONCLUSION

Our research demonstrates that successive stamen movement in S. candelabrum was accelerated by favorable weather and increased pollinator visits, which may promote pollen export. Moreover, incremental pollen packaging is likely an adaptation to seasonal regularity in variations of sex ratio resulting from protandry.

Effect of temporal changes in stamen position on reproductive success in flowers with many stamens: Manipulations of stamen position

PREMISE

Male and female reproductive success is enhanced (increased outcrossing and seed production, respectively) by stamen movement in species that have few stamens per flower. Does such enhancement also occur in species that have many stamens per flower?

METHODS

We examined the effects of stamen movement on male and female reproductive success in Anemone flaccida, which has many stamens per flower. We measured stamen movement, including temporal changes in anther-stigma and anther-anther distances. We experimentally fixed stamens in their pre- or post-movement positions.

RESULTS

The anthers moved horizontally away from the stigmas with increasing flower age, thus reducing female-male interference. The dehisced anthers tended to move farther from the stigmas, while the undehisced or dehiscing anthers remained closer to them. The number of anthers touched per flower visit was higher in flowers whose stamens were fixed in the pre-movement position than in flowers whose stamens were fixed in the post-movement position or in flowers that were not manipulated. Thus, this position may promote male reproductive success. Seed production was lower for the untreated flowers than for those with stamens fixed in the post-movement position, suggesting that the post-movement stamen position is advantageous and stamen movement is suboptimal for female reproductive success.

CONCLUSIONS

Stamen movement promotes male reproductive success in the early flowering stage and female reproductive success in the late flowering stage. In species having many stamens per flower, female-male interference can be reduced, but not eliminated, by stamen movement due to the conflict between female and male reproductive successes.

Effects of continuous variation in vertical and lateral herkogamy on reproductive success in Euphorbia fischeriana (Euphorbiaceae)

Continuous variation in herkogamy has been well reported, however, less attention has been paid to the phenomena that the consecutive expression of two types of herkogamy in the same flower. Euphorbia fischeriana, which have both vertical and lateral herkogamy, show vertical herkogamy during the female phase. However, their gynophores bend to one side with the male phase and show lateral herkogamy. In this study, we observed the effect of successive sexual organs movement on variation in herkogamy traits. By artificially manipulating the flower to present gynophore straightened in the floral center or bend to one side, we attempted to investigate whether herkogamy movement affects pollinator access efficiency, pollen removal and deposition, and seed set ratio. Furthermore, we conducted artificial pollination in the female phase to evaluate the effect of changes in pollination environment on the variations in herkogamy traits. The results showed that gynophore straightened in female phase favors pollen deposition, whereas gynophore bending in male phase was conducive to the removal of pollen. Visitation frequency, pollen deposition and removal, and seed set ratio decreased significantly when the gynophore movement was manipulated. Finally, the bending of gynophore was obviously promoted by pollination. Therefore, the continuous variation of herkogamy in the same flower of E. fischeriana caused by the bending of the gynophore could improve the accuracy of pollination and avoid the interference of the ovary with access efficiency. That may be an adaptive strategy when pollinators are scarce. Furthermore, our study also provides good support for the hypothesis that variations in herkogamy traits are strongly selected by differences in pollination environments.

Pollination adaptations of group-by-group stamen movement in a meadow plant with temporal floral closure

Floral sexual organ (stamen and pistil) movements are selective adaptations that have different functions in male-female reproduction and the evolution of flowering plants. However, the significance of stamen movements in the spatial-temporal function and separation of male and female organs has not been experimentally determined in species exhibiting floral temporal closure. The current study investigated the role of slow stamen (group-by-group) movement in male-female sexual function, and the effect of stamen movement on pollen removal, male-male and male-female interference, and mating patterns of Geranium pratense, a plant with temporal floral closure. This species uses stamen group-by-group movement and therefore anther-stigma spatial-temporal separation. Spatial separation (two whorls of stamen and pistil length) was shown to be stronger than temporal separation. We found that stamen movements to the center of the flower increase pollen removal, and the most common pollinators visited more frequently and for longer durations during the male floral stage than during the female floral stage. Petal movements increased both self-pollen deposition rate and sexual interference in G. pratense. The fruit and seed set of naturally and outcrossed pollinated flowers were more prolific than those of self-pollinated flowers. Group-by-group stamen movement, dehiscence of stamens, pistil movement, and male-female spatial-temporal functional separation of G. pratense before floral temporal closure may prevent male-female and stamen-stamen interference and pollen discounting, and may increase pollen removal and cross-pollination.