Effects of pollinia removal and insertion on flower longevity inChloraea alpina (Orchidaceae)

Summary Although it is known that stigmatic pollen deposition may trigger early flower senescence, the existence of a similar plastic response of flower lifespan to pollen removal has been much less studied. Here we report on a factorial, manipulative experiment in which all 2 × 2 flower combinations of pollinia removal and stigmatic pollinia insertion were performed in inflorescences of the Patagonian ground orchidChloraea alpina. This experiment was conducted in the laboratory, in a population of cut inflorescences and in the field. We hypothesized that if expected fitness gains, through both the male and female functions, were weighed against the costs of flower maintenance, then early flower senescence should be triggered by either pollinia removal or insertion. The shortest flower lifespan would be expected in flowers where both processes occurred. Results showed that flower longevity was very strongly affected by pollinia insertion, reducing the flower lifespan by approximately 60%. The response of pollinia removal was much weaker. A significant reduction in flower longevity caused by pollinia removal was only detected in unpollinated flowers (i.e. no pollinia inserted). Within the racemose inflorescences, flowers in basal positions lived longer than flowers in terminal ones, which might be evidence of the importance of resource availability in determining maximum flower longevity. The observed responses of flower lifespan plasticity to pollinia manipulation only partially supported our expectations based on fitness benefit—cost relationships. Other factors that might explain these discrepancies are the different fitness gains that may indeed accrue to the processes of pollinia removal and insertion as they occur in nature, donor manipulation of the recipient flower lifespan associated with the evolution of pollen clustering into pollinia and physiological constraints in terms of the extent to which flower longevity may respond to pollen removal.     

In nomen omen: the effect of flower distance on female reproductive success of the lax-flowered orchid Anacamptis laxiflora (Orchidaceae)

论花距对花序松散的倒距兰(Anacamptis laxiflora)雌花繁殖成功率的影响对多花物种而言,花序结构是塑造植物吸引力的首要因素。本研究旨在揭示花序性状对植物雌花繁殖成功率的影响,以及倒距兰(Anacamptis laxiflora,一种采用欺骗性授粉策略的陆生物种)花序上的授粉规律。我们还探究了花序性状与雌花繁殖成功率之间的关系是否会因为周围植被的高度和/或种群密度的影响而改变。我们在一个天然的倒距兰种群中划定了实验区块,对每个区块内的植株个体进行计数,并将各区块按低密度和高密度进行分类;随后,在部分区块内,我们人工清除了植株周围的杂草,从而产生了同等数量的高草丛区块和低草丛区块。我们统计了这些区块中的花序性状和雌花繁殖成功率(即果实数量及其在花序上的位置),使用广义线性混合模型(GLMMs)对统计数据进行了分析,并计算出了选择梯度。我们发现所研究的所有花序性状均对雌花繁殖成功率造成了影响。特别是GLMMs的结果表明,“平均花距”是对繁殖成功规律的最佳预测因子。我们所研究的花序性状受到显著的正向选择作用,但是这些选择趋势与周围植被的高度和种群密度都紧密相关,表明当地环境背景对选择规律的形成有显著影响。雌花繁殖成功率与花朵在花序上的位置无关,这说明传粉者在花序上随机选择花朵,未见其对花序特定部位的偏好。本项研究突显出花序性状对于多花、具有欺骗性的兰花雌花繁殖成功的重要性,并证实了环境背景在调节传粉者介导的选择规律中的主导作用。     

Differential pollination success in the course of individual flower development and flowering time in Gentiana pneumonanthe L. (Gentianaceae)

The effect of flowering time and anthesis stage on fecundity of Gentiana pneumonanthe L. (Gentianaceae) in a greenhouse experiment was studied. The species is self-compatible, not apomictic, and rarely self-pollinates spontaneously. On average, flowers lived for 11.4 days, starting with a male stage of 3.6 and continuing with a female stage of 7.9 days. Pollen viability was highest during the first two days of the male stage, but never exceeded 50%. Seed-set from cross-pollination was higher earlier in the flowering period (77%) than later (63Vo). For self-pollinations, no significant difference was observed. The success of hand-pollinations declined dramatically after the fourth day of the female stage. Self-pollination yielded lower seed-set on the first day of the female stage than on the following three days. Also, there was a significant difference in seed-set between self- and cross-pollinations (25% vs 55%, respectively) only on the first day. This suggests that selection against self pollen was stronger during the first stage of the female phase and weakened as the stylar tissue aged. In conclusion, two different ways to enhance outcrossing were observed: (1) within the population's flowering period, and (2) within an individual flower's lifespan. Both may have important effects on the genetic variability of G. pneumonanthe offspring under unfavourable conditions. Wese include small population size (associated with reduced pollinator service), general pollinator scarcity, or rainy summers.     

Long pollinia on eyes: hawk-moth pollination of Cynorkis uniflora Lindley (Orchidaceae) in Madagascar

NILSSON, L. A., RABAKONANDRIANINA, E., RAZANANAIVO, R. & RANDRIAMANINDRY, J.J., 1992. Long pollinia on eyes: hawk-moth pollination of Cynorkis uniflora Lindley (Orchidaceae) in Madagascar. The pollination biology of Cynorkis uniflora Lindley (Orchidaceae) was studied on a rocky outcrop in a fragment of montane rain forest in central Madagascar. The plant was obligately pollinated by hawk-moths. Nectar was produced in a floral spur and was accessible to hawk-moths with medium-long and long tongues. All observed visits took place during the 80 min following dusk. Floral traits and visits indicated pollination association with endemic hawk-moths of the genera Nephete and Hippotion with medium tongue length and early-evening habits. The orchid pollinia had extraordinarily long caudicles (c. 16 mm) and were carried attached to the hawk-moths' eyes, thus protruding far in front of the face of the pollinator. The ratio between components of floral female and male functions within the orchid population suggested that the much elongated operative male floral parts result from strong and progressively extreme sex-specific selection for acquiring mates via hawk-moths. By far the most frequent flower-visitors of C. uniflora at the study site were long-tongued nectar thieving hawk-moths whose relative abundance probably reflected faunal imbalance caused by the destruction of nearby moth foraging habitats through deforestation.     

Functional differentiation in pollination processes among floral traits in Serapias species (Orchidaceae)

Floral displays, influencing attractiveness to insects, increase the number of pollinator visits and the efficiency of each visit in terms of pollen exchange and thus affect the plant reproductive success. Here, we conducted an in situ manipulation experiment to investigate whether the floral modifications affect reproductive success in natural orchid populations of Serapias lingua and Serapias vomeracea. We estimated male and female reproductive success of three treatment groups, disassembly of floral tube, cutting of lip, and painting of the callus surface, in terms of pollinaria removed/deposited and fruit production. Results revealed that phenotypic modification had opposite effects on reproductive success of two examine species. Indeed, reproductive success was significantly increased by the detached of the petals and sepals, and decreased, due to callus painting and lip removal, in S. lingua. On the contrary, unmanipulated plants of S. vomeracea showed significantly higher value of pollinaria removed and deposited and fruit set than manipulated ones. The differences between S. lingua and S. vomeracea agree to the different pollination strategy of examined species. S. vomeracea shows shelter imitation strategy, and thus, the disassembly of tunnel‐like corolla does not allow the insects to use the flower as a refuge, while S. lingua is a sexually deceptive orchid and therefore the opening of the flower made more visible callus (visible at a greater distance) increasing the pollinators attraction. This study provides evidence that pollinators were largely sensitive to the experimental modification of the flower phenotype, which is consistent with the presence of significant selection on individual floral characters. Our experimental investigations of the effects of variation in display on pollinator visitation provide insights into the evolution of floral morphology in orchid with shelter imitation strategy.     

Pleiotropic effects of flowering time genes in the annual crucifer Arabidopsis thaliana (Brassicaceae)

Variation in flowering time of Arabidopsis thaliana was studied in an experiment with mutant lines. The pleiotropic effects of flowering time genes on morphology and reproductive yield were assessed under three levels of nutrient supply. At all nutrient levels flowering time and number of rosette leaves at flowering varied among mutant lines. The relationship between these two traits depended strongly on nutrient supply. A lower nutrient supply first led to an extension of the vegetative phase, while the mean number of leaves at flowering was hardly affected. A further reduction resulted in no further extension of the vegetative phase and, on average, plants started flowering with a lower leaf number. At low nutrients, early flowering affected the timing of production of siliques rather than the total output, whereas late flowering was favorable at high nutrients. This may explain the fact that many plant species flower at a relatively small size under poor conditions. Flowering time genes had pleiotropic effects on the leaf length, number of rosette and cauline leaves, and number of axillary flowering shoots of the main inflorescence. Silique production was positively correlated with the number of axillary shoots of the main inflorescence; the number of axillary primordia appeared to have a large impact on reproductive yield.     

Effects of local density and flower colour polymorphism on pollination and reproduction in the rewardless orchid Dactylorhiza sambucina (L.) Soò

The rewardless orchid Dactylorhiza sambucina shows a stable flower colour polymorphism, with both yellow- and red-flowered morphs growing sympatrically. Pollination biology and breeding system were investigated to examine the effects of density of plants, colour polymorphism, inflorescence dimension, and flower position within inflorescence on male and female reproductive success in three natural populations of D. sambucina. There were significant differences among sites in the number of pollinia removed and in fruit set per inflorescence. Number of removed pollinia and capsule production in D. sambucina were independent from flower and inflorescence size or flower position. As a whole, the red morphs showed the highest number of capsules produced, while the yellow morphs had the greatest male success. The relative male and female reproductive success were independent from plant density but were significantly correlated with the yellow morph frequency at the population level. Overall, our findings show that the contribution to the total reproductive success deriving from the two colour morphs does not conform with the predictions of negative frequency-dependent selection.     

Phenotypic selection on flowering phenology and size in two dioecious plant species with different pollen vectors

Dioecious plants may be pollinated biotically by animals or abiotically via wind or water currents. It has been hypothesized that these two types of pollen vectors might impose contrasting selective pressures on plant flowering phenology. In the present study we describe the flowering phenology of two sympatric dioecious species with contrasting pollination modes: Mercurialis perennis (wind‐pollinated) and Tamus communis (insect‐pollinated). We estimated selection differentials and gradients for flowering time and flowering synchrony. As flowering time might depend on the accumulation of enough internal resources, we also estimated direct and indirect selection on plant size. Both species have male‐biased sexual ratios, and males are bigger and produce larger flower displays than females, but only in T. communis do males bloom earlier and for longer than females. Selection gradients suggest that selection tends to favor early‐flowering females of T. communis. There is no evidence of direct current selection on the flowering phenology of M. perennis. Intersexual differences in phenology fit with sex allocation and sexual selection theories. As we hypothesized, phenology of the animal‐pollinated species is under stronger selection than that of the wind‐pollinated species and we discuss the potential role of pollen vectors in shaping the flowering phenologies of the study species.     

Rainfall and flowering synchrony in a tropical shrub: Variable selection on the flowering time ofErythroxylum havanense

Summary We tested the adaptive significance of flowering synchrony by means of a quantitative analysis of selection and by flowering induction experiments with the deciduous shrubErythroxylum havanense. Temporal schedules of flower and fruit production were determined for a local population (in three sites) in a Mexican seasonal forest for 2 years (1987–1988). The consequences of natural variation in flowering time (flowering initiation day) on maternal reproductive success (fecundity) were evaluated. We observed high levels of inter- and intraindividual flowering synchrony in 1987, but not in 1988 and this contrast was related to differences in rainfall patterns between the two years. A significant proportion (15.4%) of the phenotypic variation in flowering initiation day was accounted for by environmental variance. The expression of phenotypic variance of flowering time and, consequently, the opportunity for selection to act, are controlled by annual variation in rainfall. Despite the between-year difference in flowering synchrony, we detected a relatively intense directional selection on flowering initiation day in both years, but selection coefficients were of opposite sign (standardized directional gradients were –0.326 and 0.333 for 1987 and 1988, respectively). For both years there was a significant relationship between individual relative fitness and the number of neighbouring flowering plants in a given day, suggesting positive frequency-dependent selection.     

Effect of pollination success on floral longevity in the orchid Calypso bulbosa (Orchidaceae)

The lifespan of an individual flower is often affected by pollination success. Species differ regarding whether male function (pollen removal), female function (pollen deposition), or both trigger floral senescence. We studied senescence in the singleflowered, deceptive orchid Calypso bulbosa by manipulating the degree of male and female reproductive success. We found that deposition of any amount of pollen resulted in dramatic changes in shape and color within 4 d, whereas unmanipulated flowers and those that had had pollinia removed remained unchanged for 8-11 d after treatment. Selection may favor the reproductive function that is less easily satisfied as the trigger for senescence, because a flower that senesces after accomplishment of this function is likely to have already succeeded at the more easily satisfied one. Deceptive (i.e., rewardless) flowers are more likely to satisfy male than female function since the latter requires that a pollinator be fooled twice, first to pick up pollen and second to deposit it. A survey of naturally pollinated Calypso showed that male function, pollinium removal, was more likely to occur than female function, deposition (95% vs. 66% of visited flowers); thus floral senescence in Calypso is triggered by achievement of the function less likely to succeed. Studies of senescence triggers in species in which female function is more likely to be achieved than male are necessary to further test this hypothesis.     

Effects of human disturbance on reproductive success and population viability of Serapias cordigera (Orchidaceae)

Fragmentation of habitats by roads, railroads, fields, buildings and other human activities can affect population size, pollination success and fruit production, especially in plants showing pollinator limitation, such as Mediterranean orchids. In this study, we investigated the effect of human activity on the population dynamics and reproductive success of the orchid Serapias cordigera. Three anthropic and three natural populations were monitored over 14 years (1999–2012), classifying individuals into five stage classes and evaluating reproductive success. Population growth rates differed between anthropic and natural populations. Our results demonstrated that small anthropic populations have lower population viability compared with large natural populations. The proportion of flowering plants, the number of reproductive plants and the percentage of fruits were significantly lower in anthropic than in natural populations. This strong decline in fruit production in populations in urban areas may reflect lower pollination attraction and higher inbreeding in small than in natural populations. Calculation of extinction probabilities showed that the anthropic populations will drop below the survival threshold of 15–20 years. This study highlights that continued monitoring is needed to improve information on population viability and for appropriate conservation management. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 408–420.     

Beetle pollination of Shorea parvifolia (section Mutica, Dipterocarpaceae) in a general flowering period in Sarawak, Malaysia

Pollination ecology of an emergent tree species, Shorea (section Mutica) parvifolia (Dipterocarpaceae), was studied using the canopy observation system in a lowland dipterocarp forest in Sarawak, Malaysia, during a general flowering period in 1996. Although the species has been reported to be pollinated by thrips in Peninsular Malaysia, our observations of flower visitors and pollination experiments indicated that beetles (Chrysomelidae and Curculionidae, Coleoptera) contributed to pollination of S. parvifolia in Sarawak. Beetles accounted for 74% of the flower visitors collected by net-sweeping, and 30% of the beetles carried pollen, while thrips accounted for 16% of the visitors, and 12% of the thrips carried pollen. The apical parts of the petals and pollen served as a reward for the beetles. Thrips stayed inside the flower almost continuously after arrival, and movements among flowers were rare. Fruit set was significantly increased by introduction of beetles to bagged flowers, but not by introduction of thrips. Hand-pollination experiments and comparison of fruit set in untreated, bagged, and open flowers suggested that S. parvifolia was mainly outbreeding.     

A ballistic pollen dispersal system influences pollination success and fruit‐set pattern in pollinator‐excluded environments for the endangered species Synaphea stenoloba (Proteaceae)

The critically endangered Synaphea stenoloba (Proteaceae) has numerous scentless flowers clustered in dense inflorescences and deploys a ballistic pollen ejection mechanism to release pollen. We examined the hypothesis that active pollen ejection and flowering patterns within an inflorescence influence the reproductive success (i.e. fruit formation) of individual flowers within or among inflorescences of S. stenoloba in a pollinator‐excluded environment. Our results showed that: (1) no pollen grains were observed deposited on the stigma of their own flower after the pollen ejection system was manually activated, indicating self‐pollination within an individual flower is improbable in S. stenoloba; (2) fruit set in the indoor open pollination treatment and the inflorescence‐closed pollination treatment indicated that S. stenoloba is self‐compatible and pollen ejection can potentially result in inter‐floral pollination success; (3) fruit set in the inflorescence‐closed pollination treatment was significantly lower than that of indoor open pollination, indicating within‐ and between‐flower pollination events in an inflorescence are most likely limited, with pollination between inflorescences providing the highest reproductive opportunity; and (4) analysis of the spatial distribution of cumulative fruit set on inflorescences showed that pollen could reach any flower within an inflorescence and there was no functional limitation on seed set among flowers located at various positions within the inflorescence. These data suggest that the pollen ejection mechanism in S. stenoloba can enhance inter‐plant pollination in pollinator‐excluded environments and may suggest adaptation to pollinator scarcity attributable to habitat disturbance or competition for pollinators in a diverse flora. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 59–68.     

Reproductive isolation and pollination success of rewarding Galearis diantha and non-rewarding Ponerorchis chusua (Orchidaceae)

Background and Aims

Increasing evidence challenges the conventional perception that orchids are the most distinct example of floral diversification due to floral or prezygotic isolation. Regarding the relationship between co-flowering plants, rewarding and non-rewarding orchids in particular, few studies have investigated whether non-rewarding plants affect the pollination success of rewarding plants. Here, floral isolation and mutual effects between the rewarding orchid Galearis diantha and the non-rewarding orchid Ponerorchis chusua were investigated.

Methods

Flowering phenological traits were monitored by noting the opening and wilting dates of the chosen individual plants. The pollinator pool and pollinator behaviour were assessed from field observations. Key morphological traits of the flowers and pollinators were measured directly in the field. Pollinator limitation and interspecific compatibility were evaluated by hand-pollination experiments. Fruit set was surveyed in monospecific and heterospecific plots.

Key Results

The species had overlapping peak flowering periods. Pollinators of both species displayed a certain degree of constancy in visiting each species, but they also visited other flowers before landing on the focal orchids. A substantial difference in spur size between the species resulted in the deposition of pollen on different regions of the body of the shared pollinator. Hand-pollination experiments revealed that fruit set was strongly pollinator-limited in both species. No significant difference in fruit set was found between monospecific plots and heterospecific plots.

Conclusions

A combination of mechanical isolation and incomplete ethological isolation eliminates the possibility of pollen transfer between the species. These results do not support either the facilitation or competition hypothesis regarding the effect of nearby rewarding flowers on non-rewarding plants. The absence of a significant effect of non-rewarding P. chusua on rewarding G. diantha can be ascribed to low levels of overlap between the pollinator pools of two species.     

Directional selection on initial flowering date in Phlox drummondii (Polemoniaceae)

The fitness effects due to initial flowering date in Phlox drummondii were determined for three populations in central Texas (USA) over 3 yr (1990-1992). Mean fitness (seed set) always decreased with the later initiation of flowering. The likelihood of a plant fruiting differed with flowering date in five of the six instances (population by year combinations). Though plants that initiated flowering later tended to have spent more time in the vegetative stage and tended to die later in the year than did earlier flowering plants, this was not sufficient to overcome the reproductive penalties of flowering late. Plants that initiated flowering later in the season spent less time in the adult phase and were smaller. The mean number of flowers, fruits, and seeds per flowering plant always decreased with later flowering. Fruit set was negatively correlated with flowering date in four of the six population by year combinations. Nonparametric fitness functions were used to summarize predicted fitness among different initial flowering dates for each population on a yearly basis. Predicted mean fitness always declined nonlinearly with later flowering; the earliest flowering plants always had the highest predicted fitness. These fitness functions describe directional selection for the early initiation of flowering.     

On the mechanism of floral shifts in speciation: gained pollination efficiency from tongue- to eye-attachment of pollinia in Platanthera (Orchidaceae)

This work explores the mechanism of floral shifts that may result in speciation. The model organisms chosen were the moth-pollinated pollinator-limited orchid species Platanthera bifolia and P. chlorantha . P. bifolia exhibits tongue-attachment of pollinia on pollinators, a character state that has been found previously to be ancestral. The close relative P. chlorantha exhibits the derived state of eye-attachment of pollinia on pollinators. We reasoned that differences between the species in pollination efficiency could give insights into the mechanism of floral shifts and thus cladogenesis. Four populations per species were investigated. In three populations, where the species were growing intermixed and were sharing pollinators, there was significant difference in the pollen export and import efficiency per visit-night (night with pollen export and/or import) between the two species. P. bifolia exported pollinia more efficiently but imported pollen less efficiently than did P. chlorantha . Pollen import was 1.7–4 times faster in P. chlorantha (eye-attachment) than it was in P. bifolia (tongue-attachment). P. chlorantha had a lower risk of interference between pollen import and export. An increase in fitness through greater speed and efficiency of pollen import due to an enlargement of the stigmatic surface and a reduction in the risk of sexual interference may therefore be mechanisms of the floral shift from tongue- to eye-attachment of pollinia on pollinators.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 481–495.     

Beetle pollination and flowering rhythm ofAnnona spp. (Annonaceae) in Brazil

Dynastid scarab beetles are the main or exclusive pollinators ofAnnona spp. with large flowers and wide floral chambers. These nocturnal beetles are attracted by the characteristic odours which are caused by measurable temperature elevation of the flowers up to 10°C or even 15°C above the ambient air temperature. TheAnnona spp. investigated showed different floral rhythms varying from one to three days. The elaborate and wellcoordinated flowering processes, along with floral heating and olfactorial attraction of the night-activeCyclocephala spp., result in a very precise and effective pollination. The floral chamber provides alimentation for the beetles in the form of nutritious food-tissues and pollen and offers a mating place and a well developed shelter against predation and environmental changes. A staggered flowering period and an alternative attraction of different beetle species seems to be more a device for diminishing competition between the cooccurringAnnona spp. than a hybridization barrier.     

Evolution,pollination, and systematics of the tribeNeottieae (Orchidaceae)

The various classifications of the orchid tribeNeottieae are reviewed and a new classification is proposed that divides the tribe into three subtribes,Neottiinae, Limodorinae, andCephalantherinae, based primarily on characters of the column (gynostemium). A cladistic analysis illustrates that these three subtribes are more closely related to one another than either is to any other group in subfam.Neottioideae, although there are very few apomorphic characters for the tribe. Pollination biology is also discussed showing links between breeding systems and distribution. There is also a possible role between column and labellum morphology and the emergence of a deceptive pollination syndrome from one of reward.     

Temporal variations in the linkages between plants and flower visitors and the pollination success of Primula modesta along the snowmelt gradient

Although pollination networks between plants and flower visitors are diverse and flexible, seed production of many plant species is restricted by pollen limitation. Obligate outcrossers often suffer from low pollinator activity or severe interspecific competition for pollinator acquisition among co-flowering species. This study focused on seasonal changes in plant–flower visitor linkages in an alpine ecosystem and examined whether and how this seasonality affected the seed-set of Primula modesta, a self-incompatible distylous herb having long-tubed flowers. First, we recorded the linkages between plants and flower visitors along the snowmelt gradient. Then, pollination experiment was conducted to estimate the degree of pollen limitation over the course of flowering season of P. modesta. Flower visitors were classified by their tongue length based on the morphological matching with P. modesta flowers. As the season progressed, plant–visitor linkages became more diverse and generalized, and the visitation frequency to P. modesta flowers increased. In the later part of the season, however, the seed set of P. modesta was significantly reduced due to severe pollen limitation, presumably because of increased competition for long-tongued pollinators among co-flowering species. The present study revealed that pollinator availability for specialist species may be restricted even when plant–visitor linkages are diverse and generalized as a whole. In the case of P. modesta, morphological matching and competition for pollinators might be the main factors explaining this discrepancy.