Stamen Movement Research Articles

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

BackgroundSuccessive 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.MethodsIn 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.ResultsThe 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.ConclusionOur 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.

Pollination ecology of Ranzania japonica (Berberidaceae), a perennial plant of a monotypic genus endemic to deep‐snow regions in Japan

AbstractPlants that bloom in early spring often face constraints on reproduction, which are influenced by low temperatures and unpredictable weather conditions that affect pollinator activity. We aimed to elucidate the pollination ecology and the mating system of Ranzania japonica (Berberidaceae), a perennial plant of a monotypic genus endemic to deep‐snow regions in Japan. We documented the flowering phenology and visiting insects in the field, and conducted pollination experiments by using artificial treatments. R. japonica was suggested to be self‐incompatible but not pollen‐limited. Fruit set varied between years, and florivory seemed to have a negative influence on fruit set. Insects from various taxa were observed to visit the flowers of R. japonica, with Eusphalerum sp. (rove beetle) being the most abundant, followed by Bombylius major and hymenopteran species. The stamen movement in response to insect visits was observed. The results of the observation and the pollination treatments suggested that small‐ and medium‐sized Hymenoptera were the main pollinators and rove beetles may also contribute to pollination in R. japonica. Because early spring weather can be unsuitable for activity of bees, rove beetles may act as supplementary pollinators of R. japonica. The role of the supplementary pollinators may be an overlooked but important aspect for understanding the pollination biology of early‐spring blooming plants.

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

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? 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. 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. 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.

Flower symmetry in Saxifraga revisited

Monosymmetry in flowers has evolved many times from ancestors with polysymmetrical flowers. Flower symmetry characteristics often lack intraspecific variability. The genus Saxifraga represents an exception with high variations of floral symmetry between and within species and even within individual plants. Lab-based studies could show that this variation is to some extent caused by the flowers’ response to gravity and thus varies regularly between horizontally and vertically oriented flowers. Here, we investigate inter- and intra-individual variation in flower size, flower colouration, and floral symmetry in three species, Saxifraga stellaris, S. rotundifolia, and S. paniculata. In all three species, the stamen that initiates the sequential stamen movement is mostly downward pointing. In S. stellaris and S. paniculata, the terminal flowers are larger than the other flowers. In S. stellaris and S. rotundifolia, the size of floral guides is larger and the colour is stronger on the upward pointing 3 petals of diagonally and vertically oriented flowers, whereas the other two petals have paler or smaller floral guides. The septum between the two carpels is mostly oriented horizontally. We discuss the evolution of flower monosymmetry in regard to the morphological symmetry referring to symmetry defined by the mirror plane between carpels, petals and moving stamens, and visual symmetry defined by the pollinators view on the floral colour pattern and visible morphological features.

Plant ecology: New insights into the adaptive significance of rapid floral movements

Rapid movements by plants have been a subject of interest since Linnaeus in the 18th century. Largely lacking, however, has been a modern understanding of the adaptive significance of such movements. A recent study shows that rapid stamen movements can increase male fitness by scaring off pollinators once they have pollen placed on them.

Preliminary observations on the flower visitors ofNasa colanii(Loasaceae), a poorly known species endemic to northern Peru

Nasa is the most diverse genus among the family Loasaceae and it is mainly distributed in Peru. Most species of this genus are microendemics, with distributions restricted to very specific locations; such is the case of Nasa colanii Dostert & Weigend. This species — previously only known from the type collected in 1978 from the Amazonas region of Peru — lacks information about its biology and ecology. To improve our understanding of the reproductive biology and pollination ecology of N. colanii, we observed flower development and insect floral visits in a cloud forest in the Amazonas region. The flowers of N. colanii are nectariferous and protandrous. The typical stamen movement to the flower center of the subfamily Loasoideae appears to be autonomous. Only well-developed (elongated) pistils showed positive stigmatic receptivity to 3% hydrogen peroxide. Syrphid flies (Baccha sp.) and small beetles (Baridinae spp. and Alticini sp.) were the only observed flower visitors. The syrphid flies visited the flower and foraged for pollen, whereas the small beetles were found already in the flowers and seemingly used it as a shelter. Results suggest that N. colanii might be adapted to fly pollination.

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.

First report of osmophores and wet stigma in Podostemaceae with notes on floral biology and pollination of Weddellina squamulosa Tul.

Weddellina squamulosa floral morphology, anthesis and pollination were investigated. Anatomical and histochemical analyses were carried out to clarify the stigma type and location of putative osmophores. Although bracts, tepals, stamens, and stigmas were stained after immersion in neutral red, osmophores were detected only in the tepals. The presence of osmophores is supported by the positive test for starch, and unique micromorphology of the tepals when compared with others floral structures, such as the presence of idioblasts with lipophilic contents. These results indicated the importance of a combined approach using floral biology and anatomy to determine the presence of osmophores. Stamen movement had an important function in delaying self-pollination in the early stages of anthesis, improving the opportunity for cross-pollination and promoting self-pollination in the last hour of anthesis in case of cross-pollination failure. Halictid bees were observed collecting pollen from anthers of W. squamulosa flowers, which may promote pollination. Some attributes of W. squamulosa flowers can attract floral visitors, and others contribute to spontaneous self-pollination. There is no evidence for anemophily in this species. This is the first report of wet stigmas and description of osmophores in Podostemaceae.

Stamen movement detection of Commelina purpurea based on feature matching

The stamen movement is very important to reproduction of plant. This paper presents a feature-matching-based method to detect stamen movement of Commelina Purpurea using image processing. The regions of stamen were firstly extracted by image segmentation using thresholding. Then, the area discrimination factor of each stamen region was calculated to judge whether these stamens were adhered or not, if such adhesion did exist, the adhered stamens were segmented by watershed algorithm. After that, feature detection and matching were carried out between two adjacent frames in the image sequence in order. Then, the slope and distance statistics between the matching feature points are maded to further optimize the matching results and figure out the matching relation of different stamens in the two frames. Finally, through the matching result of different stamens in consecutive frame images, the moving trajectory of the stamens was obtained. The empirical results show that, this method can accurately segment the adhered stamens and acquire stamen trajectory of Commelina Purpurea.

Ingenious floral structure drives explosive pollination in Hydrilla verticillata (Hydrocharitaceae).

In explosive pollination, many structures and mechanisms have evolved to achieve high-speed stamen movement. The male flower of the submerged plant Hydrilla verticillata is reported to be able to release pollen explosively some time after leaving the mother plant time, but the mechanism of stamen movement and the related functional structure in this species are unclear. In this study, we observed the male flower structure and pollen dispersal process of H.verticillata. We analysed the stamen movements during the pollen dispersal process and conducted several controlled experiments to study the process of storage and release of elastic potential energy in explosive pollination. When the male flower of H. verticillata is bound to the united bracts, the sepals accumulate elastic potential energy through the expansion of basal extensor cells. After the male flower is liberated from the mother plant, the stamens unfold rapidly with the sepals under adhesion and transfer the elastic potential energy to the filament in seconds. Once stamens unfold to a critical angle, at which the elasticity of the filament just exceeds the adhesion between sepals and anthers, the stamens automatically rebound and release pollen in milliseconds. These results reveal that Catapult-like stamens, spoon-shaped sepals and enclosed united bracts in the spathe together constitute the functional structure in rapid stamen movement of H.verticillata. They ensure that the pollen can be released on the water surface, and thus adapt successfully to the pollen-epihydrophilous pollination.

Specialised protagonists in a plant-pollinator interaction: the pollination of Blumenbachia insignis (Loasaceae).

Analyses of resource presentation, floral morphology and pollinator behaviour are essential for understanding specialised plant-pollinator systems. We investigated whether foraging by individual bee pollinators fits the floral morphology and functioning of Blumenbachia insignis, whose flowers are characterised by a nectar scale-staminode complex and pollen release by thigmonastic stamen movements. We described pollen and nectar presentation, analysed the breeding system and the foraging strategy of bee pollinators. We determined the nectar production pattern and documented variations in the longevity of floral phases and stigmatic pollen loads of pollinator-visited and unvisited flowers. Bicolletes indigoticus (Colletidae) was the sole pollinator with females revisiting flowers in staminate and pistillate phases at short intervals, guaranteeing cross-pollen flow. Nectar stored in the nectar scale-staminode complex had a high sugar concentration and was produced continuously in minute amounts (~0.09μl·h-1 ). Pushing the scales outward, bees took up nectar, triggering stamen movements and accelerating pollen presentation. Experimental simulation of this nectar uptake increased the number of moved stamens per hour by a factor of four. Flowers visited by pollinators received six-fold more pollen on the stigma than unvisited flowers, had shortened staminate and pistillate phases and increased fruit and seed set. Flower handling and foraging by Bicolletes indigoticus were consonant with the complex flower morphology and functioning of Blumenbachia insignis. Continuous nectar production in minute quantities but at high sugar concentration influences the pollen foraging of the bees. Partitioning of resources lead to absolute flower fidelity and stereotyped foraging behaviour by the sole effective oligolectic bee pollinator.

The cost of fidelity: foraging oligolectic bees gather huge amounts of pollen in a highly specialized cactus–pollinator association

Abstract Plant–pollinator interactions vary along a specialization–generalization continuum. Advances in understanding the evolutionary and ecological consequences of different degrees of specialization depend on precise data on plant–pollinator interdependency. We studied the association of Parodia neohorstii (Cactaceae) and its bee pollinators focusing on pollinator foraging behaviour, flower functioning, female and male reproductive success, and pollen fate. Parodia neohorstii showed synchronized flower opening and pollen presentation but discontinuous blooming. The apparently generalized flowers partition pollen through thigmonastic stamen movements that function as a mechanical filter against generalist bees by restricting access to the major pollen reservoir to bees that show flower handling ‘know-how’, thereby favouring the oligolectic bee Arhysosage cactorum. This pollinator adjusted its pollen foraging to flower opening, removed pollen hurriedly, and promoted maximal fruit and seed set, which was minimal in its absence. Estimates of pollen fate revealed that a huge amount of pollen flows to specialized pollinators (86.5%), and only 0.9% reaches conspecific stigmas. The specialized interaction between P. neohorstii and Arhysosage cactorum, both threatened species, is efficient but fragile. Any environmental modification that causes a mismatch between the partners is likely to result in reproductive failure.

Flowers anticipate revisits of pollinators by learning from previously experienced visitation intervals

ABSTRACTPlants – and their pollinating counterparts – display complex and sophisticated mechanisms to achieve successful pollination. It probably was only a matter of time for proof of plant intelligence in the context of floral ecology to surface, i.e. the memorization of previous events and a corresponding adjustment of flower behavior. In a recent study we presented a large experimental dataset on the evolution of stamen movement patterns observed in Loasaceae and the apparent role of plant behavior in the diversification of this plant group. The findings at species level suggest that individual plants may be able to adjust the timing of their pollen presentation to the actual pollination scenario they experience. Here we provide first evidence for a pre-emptive stamen presentation in Nasa poissoniana (Loasaceae), based on previously experienced pollinator visitation intervals. Using the unique ability of fast and precise stamen movements in response to a previous stimulus of the nectar scales, the plants should be able to reduce pollen loss and increase outbreeding success via optimizing the timing of male function. We discuss this behavior and its implications in the light of the recent literature and propose questions for future investigations.

A case of behavioural diversification in male floral function \u2013 the evolution of thigmonastic pollen presentation

Obvious movements of plant organs have fascinated scientists for a long time. They have been studied extensively, but few behavioural studies to date have dealt with them, and hardly anything is known about their evolution. Here, we present a large experimental dataset on the stamen movement patterns found in the Loasaceae subfam. Loasoideae (Cornales). An evolutionary transition from autonomous-only to a combination of autonomous and thigmonastic stamen movement with increased complexity was experimentally demonstrated. We compare the stamen movement patterns with extensive pollinator observations and discuss it in the context of male mating behavior. Thigmonastic pollen presentation via stamen movements appears to be a crucial component of floral adaptation to pollinator behaviour, evolving in concert with complex adjustments of flower signal, reward and morphology. We hypothesize that rapid adjustments of pollen presentation timing may play a significant role in the diversification of this plant group, representing a striking example for the evolutionary significance of plant behaviour.

Nectary tracks as pollinator manipulators: The pollination ecology of Swertia bimaculata (Gentianaceae).

Floral nectaries are closely associated with biotic pollination, and the nectar produced by corolla nectaries is generally enclosed in floral structures. Although some Swertia spp. (Gentianaceae), including S. bimaculata, evolved a peculiar form of corolla nectaries (known as “gland patches”) arranged in a conspicuous ring on the rotate corolla and that completely expose their nectar, little is known about the pollination of these plants. Two hypotheses were made concerning the possible effects of gland patches: visual attraction and visitor manipulation. The floral traits, mating system, and insect pollination of S. bimaculata were examined, and the pollination effects of gland patches were evaluated. A comparative study was made using Swertia kouitchensis, a species with fimbriate nectaries. Swertia bimaculata flowers were protandrous, with obvious stamen movement leading to herkogamy in the female phase and to a significant reduction in nectary–anther distance. The species is strongly entomophilous and facultatively xenogamous. The daily reward provided per flower decreased significantly after the male phase. The most effective pollinators were large dipterans, and the visiting proportion of Diptera was significantly higher in S. bimaculata than in S. kouitchensis. Most visitors performed “circling behavior” in S. bimaculata flowers. Removing or blocking the nectaries caused no reduction in visiting frequency but a significant reduction in visit duration, interrupting the circling behavior. The circling behavior was encouraged by nectar abundance and promoted pollen dispersal. Visitor species with small body size had little chance to contact the anthers or stigma, revealing a filtration effect exerted by the floral design. These results rejected the “visual attraction” hypothesis and supported the “visitor manipulation” hypothesis. The nectary whorl within a flower acted like a ring‐shaped track that urged nectar foragers to circle on the corolla, making pollination in S. bimaculata flowers more orderly and selective than that in classically generalist flowers.

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

Approximately 80 % of angiosperm species produce hermaphroditic flowers, which face the problem of male-male sexual interference (one or more anthers gets in the way of disseminating pollen from other anthers) or male-female sexual interference (the pistil interferes with disseminating pollen from the anthers by preventing the anther from touching a pollinator, or the anther prevents pollinator from depositing outcross pollen on the stigma). Slow stamen movement in hermaphrodite flowers has been interpreted as an adaptation for reducing male-male sexual interference. Using slow stamen movement in Lychnis cognata (Caryophyllaceae), this study presents new evidence that this phenomenon can reduce both male-male and male-female sexual interference. Ten stamens in L. cognata flowers vertically elongated their filaments in two batches and displayed similar patterns in pollen dispensing. More importantly, 10 stamens bend out of the floral centre by curving the filament also in 2 batches and pollen grains located at the flower centre displayed the highest viability. Thus, three stages of stamen movement can be identified, comprising two male stages (M1 and M2) and one female stage (F). We found that the main pollinator for L. cognata, Bhutanitis yulongensis (Papilionodae) generally preferred M1 flowers. Manipulation experiments show that vertical stamen movement enabled the anthers to dehisce at different times to prolong the presentation of pollen grains. Horizontal movement of the stamen decreased both male-male and male-female interference. However, vertical stamen movement had a minor role in increasing amount of pollen received by the stigma. This study provides the first direct experimental evidence of concurrent male-male and male-female interference in a flower. We suggest that the selection pressure to reduce such interference might be a strong force in floral evolution. We also propose that other selective pressure, including pollen dispensing mechanisms, pollen longevity, pollinator behaviour and weather, might contribute to floral evolution.

Sequential stamen maturation and movement in a protandrous herb: mechanisms increasing pollination efficiency and reducing sexual interference.

Successive stamen movement directly controls pollen presentation schedules through sequential stamen maturation and changes the extent of herkogamy by altering the positions of sexual organs. However, the implications of such movements in terms of pollination are not well understood. Pollen presentation theory predicts that staggered pollen presentation should be favoured when plants are subject to diminishing returns on pollen transfer. Herkogamy on the other hand, has been interpreted as an adaptive trait that reduces sexual interference in hermaphrodite flowers. In this study, we conducted floral manipulations to determine the function of successive stamen movement in pollen transfer. By artificially manipulating the flowers to present two anthers simultaneously in the floral centre, we attempted to investigate whether changes in the anther presentation strategy affect pollen removal, deposition and the efficiency of pollinators. Compared with the natural treatment, the pollen transfer efficiency of halictid bees decreased significantly when the flowers were manipulated to present two anthers simultaneously. Although the presentation of two anthers simultaneously led to a similar pollen removal rate, there was a significant reduction in pollen deposition on neighbouring stigmas. To evaluate the effect of movement herkogamy on pollen export and deposition and seed set, the flowers were manipulated with or without the movement of stamen bending out from the floral centre. Pollen export decreased significantly when the central anther was moved away from the pistil, and pollen deposition and seed set declined significantly when the five spent anthers were retained on the pistil. Our study provides good support for the pollen presentation theory and provides direct experimental evidence that successive stamen movement could increase pollen transfer efficiency by sequential stamen maturation. Moreover, movement herkogamy promotes pollen export, deposition and seed set, and could therefore be regarded as an effective mechanism to reduce interference between male and female functions.

Pollination of Aosa rupestris (Hook.) Weigend (Loasaceae): are stamen movements induced by pollinators?

Inducement to stamen movement by oligolectic bees has been reported for some Loasaceae species; however, detailed research studies on the pollination ecology of species in the genus Aosa are absent. In this study, we analyzed the floral biology and breeding system of Aosa rupestris (Hook.) Weigend, focusing on the role of pollinators in inducing stamens’ movements. We described the anthesis, the behavior of floral visitors, and carried out reproductive experiments in a population in a dry forest (“caatinga”) area in Northeastern Brazil. We carried out four experiments and one control to establish whether the interval between the movements of two successive stamens is regulated by pollinator visits. Anthesis lasted for 3–4 days. Stamens (102 ± 12.57) remained with closed anther inside petals early in the anthesis, after which they moved to the center of the flower and presented its pollen (male phase). After all stamens have reached the center of the flower, the female phase started. Bicolletes nordestina Urban, 2006 was the only floral visitor to A. rupestris flowers, drinking nectar, collecting pollen, or sleeping on the flowers. Aosa rupestris was autogamous, but fruit set was higher under natural conditions. The interval between movements of two successive stamens was not different among experiments. Therefore, stamen movements were spontaneous and did not respond to pollinator visits, in contrast to the pattern of stamen movements observed in other Loasaceae species. Although A. rupestris is autogamous, floral structure and behavior of the oligolectic bee pollinator ensured the highest level of fruit set in this species.

Stamen Movement and its Biological Significance in <i>Compositae</i> Plants

There is a unique inflorescence composition and stamen structure in Compositae. Stamen structure, filament movement and its mechanism was analyzed and discussed, with cosmos and small sunflowers as experimental materials, by using morphological anatomy, microscopic measurement, tabletting observation. The results showed that: (1) There was a certain regularity in the opening of tubular floral organ in capitulum, of which their movements were initiated from outside to inside. (2) The mainly cause of stamen movement in Compositae came from the changes filaments length. (3) Stamen movement was not a simple physical movement-with filaments shortening, cell structure also has changed. (4) The filament movement in Compositae is not only beneficial to itself fully stretching, but also reduces the interference during pollen spreading.

Is There ‘Anther-Anther Interference’ within a Flower? Evidences from One-by-One Stamen Movement in an Insect-Pollinated Plant

The selective pressure imposed by maximizing male fitness (pollen dispersal) in shaping floral structures is increasingly recognized and emphasized in current plant sciences. To maximize male fitness, many flowers bear a group of stamens with temporally separated anther dehiscence that prolongs presentation of pollen grains. Such an advantage, however, may come with a cost resulting from interference of pollen removal by the dehisced anthers. This interference between dehisced and dehiscing anthers has received little attention and few experimental tests to date. Here, using one-by-one stamen movement in the generalist-pollinated Parnassia palustris, we test this hypothesis by manipulation experiments in two years. Under natural conditions, the five fertile stamens in P. palustris flowers elongate their filaments individually, and anthers dehisce successively one-by-one. More importantly, the anther-dehisced stamen bends out of the floral center by filament deflexion before the next stamen's anther dehiscence. Experimental manipulations show that flowers with dehisced anther remaining at the floral center experience shorter (1/3–1/2 less) visit durations by pollen-collecting insects (mainly hoverflies and wasps) because these ‘hungry’ insects are discouraged by the scant and non-fresh pollen in the dehisced anther. Furthermore, the dehisced anther blocks the dehiscing anther's access to floral visitors, resulting in a nearly one third decrease in their contact frequency. As a result, pollen removal of the dehiscing anther decreases dramatically. These results provide the first direct experimental evidence that anther-anther interference is possible in a flower, and that the selection to reduce such interferences can be a strong force in floral evolution. We also propose that some other floral traits, usually interpreted as pollen dispensing mechanisms, may function, at least partially, as mechanisms to promote pollen dispersal by reducing interferences between dehisced and dehiscing anthers.