Relative pollination effectiveness of floral visitors of Pitcairnia angustifolia (Bromeliaceae)

The effectiveness of flower visitors as pollinators will determine their potential role as selective agents on flower traits. Pitcairnia angustifolia has floral characters that would fit pollination by long-billed hummingbirds, and they should be the most effective pollinators for this plant. To test this prediction, we characterized the behavior of visitors toward flowers and their pollination effectiveness. Coereba flaveola (bananaquits) was the most frequent flower visitor and acted as a primary nectar robber; however, they pollinated incidentally and deposited pollen on stigmas. The endemic short-billed hummingbird Chlorostilbon maugaeus behaved as a secondary robber and did not pollinate flowers. As expected, the long-billed hummingbird, Anthracothorax viridis, was the most efficient visitor in terms of pollen deposition; however, it was the least frequent flower visitor. Introduced Apis mellifera (honeybees) were second in efficiency at depositing pollen and performed one third of the flower visits. Estimates of the expected rate of pollen deposition by each pollinator did not identify a single most effective pollinator. For P. angustifolia at least three flower visitors including an exotic bee and a nectar robber may be equally important to reproductive success. While these results limit our ability to make predictions on the role of hummingbird-pollination on current flower evolution, they do suggest the potential for pollination redundancy among flower visitors for P. angustifolia populations.     

Distyly and sequential pollinators of Psychotria nuda (Rubiaceae) in the Atlantic rain forest, Brazil

Reciprocal herkogamy is known to promote intermorph-pollination in distylous species, which are generally self- and intramorph-incompatible. Legitimate crossing rates are also influenced by pollinator foraging strategy, which determines most of the pollen flow in natural populations. This study reports on the floral morphology, compatibility relations and pollination biology of Psychotria nuda (Cham. and Schltdl.) Wawra in the Atlantic rain forest, southeastern Brazil, based on floral measurements, hand-pollination experiments and focal observation of floral visitors. It was found that P. nuda does not present an exactly reciprocal herkogamy, however, this morphological trait in P. nuda is as good as in most of Rubiaceae. Reproductive experiments showed compatibility relations similar to those frequently observed in distylous species. The hummingbirds Ramphodon naevius and females of Thalurania glaucopis were the main pollinators of P. nuda, presenting the traplining foraging strategy, which seems to maximize intermorph crosses in P. nuda flowers. These hummingbirds pollinated P. nuda flowers sequentially throughout the flowering period.     

The importance of bees as pollinators in the short corolla bromeliad Aechmea caudata in southern Brazil

The majority of bromeliad species are pollinated by vertebrates, mainly hummingbirds and bats. However, bees are among the most frequent visitors in some short-corolla species with ornithophilous features, but only few studies identified insects as pollinators of these bromeliads. The importance of visitors for pollination success in Aechmea caudata (Bromeliaceae) was determined through the frequency and pollination effectiveness (measured as seed set/single visit) of its visitors in a secondary Atlantic forest area in southern Brazil. Aechmea caudata is self-incompatible and therefore pollinator-dependent. A total of 16 species were recorded visiting their flowers. Bees were the most rich and frequent taxon (91% of 647 visits). Bombus morio was the most frequent species (41%). Although the floral features of A. caudata, such as scentless, tubular corollas, yellow and red flowers, and nectar secretion during the whole diurnal anthesis, are related to ornithophily, the single hummingbird species Thalurania glaucopis failed to pollinate the flowers. Its low frequency (2.5%) apparently did not promote the pollen flux between conspecific bromeliads. Pollination tests showed that no seeds developed after hummingbird visits. Seeds were formed only at flowers visited by B. morio. We discuss our findings by contrasting them with the results on the similar and sympatric A. lindenii and by emphasizing the importance of bees for pollination of bromeliads with short corolla. Our results show that pollination effectiveness together with frequency data are necessary to analyze the complex interactions between plants and their flower visitors.     

异型花柱植物喀什补血草的传粉者功能群与花粉转移效率

异型花柱是受遗传控制的花柱多态现象, 被达尔文认为是植物通过在传粉者体表不同部位滞落花粉以促进型间花粉准确传递的一种适应。该现象虽已受到广泛关注, 但在一些花型变异较大且不稳定的传粉系统中, 不同传粉者对各花型繁殖所产生的影响仍知之甚少。该研究以分布于新疆天山南坡的一个有同长花柱共存的异型花柱植物喀什补血草(Limonium kaschgaricum)种群为研究对象, 对其花型构成及频率、传粉者及花粉转移效率等进行了调查分析。结果表明: 1)种群中除了存在雌/雄蕊长度交互对应的长(L)/短(S)花柱型花外, 还有雌/雄蕊同长的花(H型), 且各花型花的花冠口直径、花冠筒长及花粉量等参数间无差异, 但花粉纹饰和柱头乳突细胞形态具二型性。其中, H型花的花粉和柱头形态与L型花(或S型花)的一致。2)花型内和自花授粉均不亲和; 型间授粉时, 花粉和柱头形态不同的花型间亲和, 反之不亲和。3)种群内存在长/短吻两类传粉昆虫。在以短吻传粉者为主的盛花初、中期, L和H型花柱头上的异型花粉数均显著高于S型花的, 且L和S型花高位性器官间的异型花粉传递效率高于低位性器官间的; 而在以长吻传粉者为主的盛花后期, L和S型花的柱头间异型花粉数无显著差异, 且高/低位性器官间具有相同的异型花粉转移效率; 与传粉者出现时期相对应的、在花期不同阶段开放花的结实率也明显不同。4)长/短吻昆虫具明显不同的传粉功能, 短吻昆虫只能对L和H型花进行有效传粉, 且访花频率和型间花粉转移效率较低, 为低效传粉者; 而长吻昆虫对各花型均能有效传粉, 具高的访花频率和型间花粉转移效率, 为高效传粉者。因为长吻昆虫的阶段性出现所形成的不稳定传粉系统, 使低效的短吻昆虫可能会成为种群中花型变异的驱动力, 并使S型花受到更大的选择压力。H型花克服了柱头缩入的弊端, 可能会成为不稳定传粉系统下的一个替代花型而持续存在。     

Plant–hummingbird interactions in the West Indies: floral specialisation gradients associated with environment and hummingbird size

Floral phenotype and pollination system of a plant may be influenced by the abiotic environment and the local pollinator assemblage. This was investigated in seven plant–hummingbird assemblages on the West Indian islands of Grenada, Dominica and Puerto Rico. We report all hummingbird and insect pollinators of 49 hummingbird-pollinated plant species, as well as six quantitative and semi-quantitative floral characters that determine visitor restriction, attraction and reward. Using nonmetric multidimensional scaling analysis, we show that hummingbird-pollinated plants in the West Indies separate in floral phenotypic space into two gradients—one associated with the abiotic environment and another with hummingbird size. Plants pollinated by large, long-billed hummingbirds had flowers with long corolla tube, large amounts of nectar and showy orange-red colouration. These attracted few or no insect species, whereas plants pollinated by small, short-billed hummingbirds were frequently pollinated by insects, particularly lepidopterans. The separation of plants related to environmental factors showed that species in the wet and cold highlands produced large amounts of dilute nectar, possessed no or a weak odour, and were associated with few insects, particularly few hymenopterans, compared to plants in the dry and warm lowlands. The most specialised hummingbird-pollinated plants are found in the West Indian highlands where they are pollinated by mainly large, long-billed hummingbirds. At the other extreme, highly generalised plants growing in the dry and warm lowlands are pollinated by small, short-billed hummingbirds and numerous insect species. This illustrates that, even within the hummingbird-pollinated flora, pollination syndrome and the degree of specialisation may vary tremendously depending on pollinator morphology and environment. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Pollination biology of Canna indica (Cannaceae) with particular reference to the functional morphology of the style

The anatomy of the bizarre style of Canna indica is analyzed functionally and comparatively within Zingiberales, particularly in relation to the presence of two stigma-like areas, one apical and the other lateral and subapical. We asked whether these areas have separate receptive or adhesive functions and whether they are derived from a single stigma that previously had both functions. We expected that the mechanism of pollen transference would be highly effective at the flower level, i.e., that pollen limitation would affect fruit set rather than seed set. Both areas produce a sticky carbohydrate- and mucilage-positive exudate but only the apical one leads to pollen tube growth into the stylar canal. The subapical and lateral area is regarded here as being homologous to the viscidium of Lowiaceae and Marantaceae. High pollen limitation through fruit set is attributable to the low visitation rate of the single long-billed hummingbird pollinator (Heliomaster furcifer) and to pollen loss caused by nectar robbers, while low limitation through seed set suggests that the efficiency of a few visits of pollen-carrying hummingbirds is high. Recordings of the pollination process indicate that the viscidium is touched before the pollen presenter, when hummingbirds are flying out of the flowers.     

Stigmatic fluid aids self-pollination in Roscoea debilis (Zingiberaceae): a new delayed selfing mechanism

Background and Aims

Delayed selfing is the predominant mode of autonomous self-pollination in flowering plants. However, few delayed selfing mechanisms have been documented. This research aims to explore a new delayed selfing mechanism induced by stigmatic fluid in Roscoea debilis, a small perennial ginger.

Methods

Floral biology and flower visitors were surveyed. The capacity of autonomous selfing was evaluated by pollinator exclusion. The timing of autonomous selfing was estimated by emasculation at different flowering stages. The number of seeds produced from insect-pollination was assessed by emasculation and exposure to pollinators in the natural population. The breeding system was also tested by pollination manipulations.

Key Results

Autonomous self-pollination occurred after flowers wilted. The stigmatic fluid formed a globule on the stigma on the third day of flowering. The enlarged globule seeped into the nearby pollen grains on the fourth flowering day, thus inducing pollen germination. Pollen tubes then elongated and penetrated the stigma. Hand-selfed flowers produced as many seeds as hand-crossed flowers. There was no significant difference in seed production between pollinator-excluded flowers and hand-selfed flowers. When emasculated flowers were exposed to pollinators, they produced significantly fewer seeds than intact flowers. Visits by effective pollinators were rare.

Conclusions

This study describes a new form of delayed autonomous self-pollination. As the predominant mechanism of sexual reproduction in R. debilis, delayed self-pollination ensures reproduction when pollinators are scarce.     

Changes in Florets’ Vertical Direction within Inflorescence Affects Pollinator Behavior,and Fitness in <i>Trifolium repens</i>

Ecological interactions between flowers and pollinators greatly affect the reproductive success. To facilitate these interactions, many flowers are known to display their attractive qualities, such as scent emission, flower rewards and floral vertical direction, in a rhythmic fashion. However, less is known about how plants regulate the relationship between these flower traits to adapt to pollinator visiting behavior and increase reproduction success. Here we investigated the adaptive significance of the flower bending from erect to downward in Trifolium repens. We observed the flowering dynamic characteristics (changes of vertical direction of florets, flowering number, pollen grain numbers, pollen viability and stigma receptivity over time after blossom) and the factors affecting the rate of flower bending in T. repens. Then we altered the vertical direction of florets in inflorescence of different types (upright and downward), and compared the pollinator behaviors and female reproductive success. Our results showed that florets opened sequentially in inflorescence, and then bend downwards slowly after flowering. The bending speed of florets was mainly influenced by pollination, and bending angle increased with the prolongation of flowering time, while the pollen germination rate, stigma receptivity and nectar secretion has a rhythm of “low-high-low” during the whole period with the time going. The visiting frequency of all the four species of pollinators on upward flowers was significantly higher than that of downward flowers, and they especially prefer to visit flowers with a bending angle of 30°–60°, when the flowers was exactly of the highest flower rewards (nectar secretion and number of pollen grains), stigma receptivity and pollen germination rate. The seed set ratio and fruit set ratio of upward flowers were significantly higher than downward flowers, but significantly lower than unmanipulated flowers. Our results indicated that the T. repens could increase female and male fitness by accurate pollination. The most suitable flower angle saves pollinators’ visiting energy and enables them to obtain the highest nectar rewards. This coordination between plants and pollinators maximizes the interests of them, which is a crucial factor in initiating specialized plant-pollinator relationships.     

The pollination biology of two species of Helicteres (Malvaceae) with different mechanisms of pollen deposition

Species of Helicteres are pollinated mainly by hummingbirds and bats. Most species pollinated by hummingbirds have a mechanism of depositing pollen on the top of the pollinator's head such as is shown in this work for Helicteres sacarolha. H. brevispira has an unusual mechanism of depositing pollen grains under the tail or on the abdomen of the hummingbirds. The top of the birds’ head may be considered an efficient place to transport pollen grains, because it is plain, easily accessible for deposition and donation of pollen and not easily accessible for grooming, while the tail is movable and inclined. Thus, H. brevispira pollinators may carry or transfer fewer amounts of pollen grains than H. sacarolha pollinators from one flower to another. If a large amount of pollen grains is lost, a higher quantity of flower or pollen has to be produced to guarantee reproductive success. Plants of H. brevispira set higher number of flowers and pollen grains per flower than H. sacarolha and have also higher rates of fruit and flower abortion. Thus, pollination efficiency of H. brevispira may be reached by high pollen and flower production. Flower change mechanism presented in this species may be also involved with the optimization of pollinator feeding and pollination efficiency.     

Effectiveness of nectarivorous birds and honeybees as pollinators of Banksia spinulosa (Proteaceae)

Abstract The effectiveness of nectarivorous birds and honeybees (Apis mellifera) as pollinators of Banksia spinulosa (Proteaceae) was investigated. Birds visited inflorescences in the early, mid and late flowering seasons. In contrast, honeybees visited only on days in the late flowering period when maximum temperatures exceeded 15°C. Self pollen remained on pollen presenters of flowers for up to 5 days in the early and mid periods. In the late period, when honeybees visited inflorescences, self pollen was removed within 2 days. Pollen removal was similar for caged (birds excluded) and open inflorescences in the late period, indicating that most pollen was removed by honeybees. In the early and mid periods, honeyeaters pollinated 22% and 27% of flowers on open inflorescences, respectively. In the late period, when both birds and bees visited inflorescences, 64–73% of flowers on open inflorescences were pollinated. Foraging by honeybees resulted in pollen deposition as 38% of flowers on caged inflorescences were pollinated. Throughout the flowering season a similar number of pollen grains was deposited per stigma. There were 3.0–3.7 pollen grains per stigma on open inflorescences in the late period, although only 2.0 grains per stigma on caged inflorescences. In the early and mid periods, fewer caged than open inflorescences produced fruits, indicating the importance of honeyeaters to reproductive success at these times. In contrast, in the late period when honeybees visited inflorescences, fruit-set was similar on caged and open inflorescences. Overall, these results indicate that honeybees were effective pollinators of B. spinulosa.     

A generalized pollination system in the tropics: bats, birds and Aphelandra acanthus

Background and Aims

A number of different types of flower-visiting animals coexist in any given habitat. What evolutionary and ecological factors influence the subset of these that a given plant relies on for its pollination? Addressing this question requires a mechanistic understanding of the importance of different potential pollinators in terms of visitation rate (pollinator ‘quantity’) and effectiveness at transferring pollen (pollinator ‘quality’) is required. While bat-pollinated plants typically are highly specialized to bats, there are some instances of bat-pollinated plants that use other pollinators as well. These generalized exceptions tend to occur in habitats where bat ‘quantity’ is poor due to low or fluctuating bat densities.

Methods

Aphelandra acanthus occurs in tropical cloud forests with relatively high densities of bat visitors, yet displays a mix of floral syndrome characteristics, suggesting adaptation to multiple types of pollinators. To understand its pollination system better, aspects of its floral phenology and the ‘quantity’ and ‘quality’ components of pollination by its floral visitors are studied here.

Key Results

Flowers were found to open and senesce throughout the day and night, although anther dehiscence was restricted to the late afternoon and night. Videotaping reveals that flowers are visited nocturnally by bats and moths, and diurnally by hummingbirds. Analysis of pollen deposition shows that bats regularly transfer large amounts of conspecific pollen, while hummingbirds occasionally transfer some pollen, and moths rarely do so.

Conclusions

Hummingbirds and bats were comparable in terms of pollination ‘quantity’, while bats were the most effective in terms of ‘quality’. Considering these components together, bats are responsible for approx. 70 % of A. acanthus pollination. However, bats also transferred remarkably large amounts of foreign pollen along with the conspecific grains (three of four grains were foreign). It is suggested that the negative effects of interspecific pollen transfer may decrease bat ‘quality’ for A. acanthus, and thus select for generalization on multiple pollinators instead of specialization on bats.Key words: Specialization, generalization, pollinator effectiveness, hummingbirds, floral syndrome, bat pollination, chiropterophily, ornithophily, cloud forest, heterospecific pollen transfer     

The bumblebee Bombus ardens ardens (Hymenoptera: Apidae) visits white clover in orchards before Oriental persimmon blooms

Flowers on the ground of orchards can provide substantial resources for wild pollinators of orchard trees. Few studies, however, have examined the relative importance of groundcover flowers to orchard pollination by analyzing pollen on the body surface of pollinators. Oriental persimmon trees bloom within the longer blooming period of white clover, which is occasionally found as a flowering plant on the ground of persimmon orchards in Japan. The present study compared the insect species assemblage collected on persimmon flowers with that on clover. Before persimmon bloomed, Bombus ardens ardens and Apis cerana japonica were the major visitors of clover flowers. Once persimmon bloomed, the former was the most abundant bee that visited persimmon flowers over the flowering period. Apis mellifera was captured only on clover flowers. We found numerous clover pollen grains on the body surface of bumblebees captured on persimmon flowers, but far fewer persimmon pollen grains on bees that visited clover. These findings show that B. ardens ardens utilized the clover flowers under the orchards before persimmon bloomed.     

Nectar secretion dynamic links pollinator behavior to consequences for plant reproductive success in the ornithophilous mistletoe Psittacanthus robustus

The mistletoe Psittacanthus robustus was studied as a model to link flower phenology and nectar secretion strategy to pollinator behaviour and the reproductive consequences for the plant. The bright‐coloured flowers presented diurnal anthesis, opened asynchronously throughout the rainy season and produced copious dilute nectar as the main reward for pollinators. Most nectar was secreted just after flower opening, with little sugar replenishment after experimental removals. During the second day of anthesis in bagged flowers, the flowers quickly reabsorbed the offered nectar. Low values of nectar standing crop recorded in open flowers can be linked with high visitation rates by bird pollinators. Eight hummingbirds and two passerines were observed as potential pollinators. The most frequent flower visitors were the hummingbirds Eupetomena macroura and Colibri serrirostris, which actively defended flowering mistletoes. The spatial separation between anthers, stigma and nectar chamber promotes pollen deposition on flapping wings of hovering hummingbirds that usually probe many flowers per visit. Seed set did not differ between hand‐, self‐ and cross‐pollinated flowers, but these treatments set significantly more seeds than flowers naturally exposed to flower visitors. We suggest that the limitation observed in the reproductive success of this plant is not related to pollinator scarcity, but probably to the extreme frequency of visitation by territorial hummingbirds. We conclude that the costs and benefits of plant reproduction depend on the interaction strength between flowers and pollinators, and the assessment of nectar secretion dynamics, pollinator behaviour and plant breeding system allows clarification of the complexity of such associations.     

Reproductive system and fitness of Vriesea friburgensis,a self‐sterile bromeliad species

Reproductive biology and plant fertility are directly related to many aspects of plant evolution and conservation biology. Vriesea friburgensis is an epiphytic and terrestrial bromeliad endemic to the Brazilian Atlantic rainforest. Hand‐pollination experiments were used to examine the reproductive system in a wild population of V. friburgensis. Plant fertility was assigned considering flower production, fruit and seed set, seed germination, and pollen viability. Self‐sterility observed from spontaneous selfing and manual self‐pollination treatments may be the consequence of late‐acting self‐incompatibility. Hand‐pollination results indicated no pollen limitation in the population studied. Floral biology features such as a few daily open flowers, nectar production, and sugar concentration corroborate hummingbirds as effective pollinators, although bees were also documented as pollinators. Components of fitness such as high flower, fruit, and seed production together with high seed and pollen viability indicate that this wild population is viable. From a conservation point of view, we highlight that this self‐sterile species depends on pollinator services to maintain its population fitness and viability through cross‐pollination. Currently, pollinators are not limited in this population of V. friburgensis. Conversely, the maintenance and continuous conservation of this community is essential for preserving this plant–pollinator mutualism.     

In the right place at the right time: Parnassia resolves the herkogamy dilemma by accurate repositioning of stamens and stigmas

Background and Aims

Spatial (herkogamy) and temporal (dichogamy) separation of pollen presentation and stigma receptivity have been interpreted as reducing interference between male and female functions in hermaphroditic flowers. However, spatial separation leads to a potential conflict: reduced pollination accuracy, where pollen may be placed in a location on the pollinator different from the point of stigma contact.

Methods

To understand better how herkogamous flowers resolve this conflict, a study was made of a subalpine herb, Parnassia epunctulata, the nectariferous flowers of which exhibit sequential anther dehiscence (staggered pollen presentation) and stamen movements; usually one newly dehisced anther is positioned each day over the central gynoecium, while the older stamens bend away from the central position.

Key Results

The open flowers were visited by a variety of pollinators, most of which were flies. Seed set was pollinator-dependent (bagged flowers set almost no seeds) and pollen-limited (manual pollination increased seed set over open pollination). Analyses of adaptive accuracy showed that coordinated stamen movements and style elongation (movement herkogamy) dramatically increased pollination accuracy. Specifically, dehiscing anthers and receptive stigmas were positioned accurately in the vertical and horizontal planes in relation to the opposite sexual structure and pollinator position. By contrast, the spatial correspondence between anthers and stigma was dramatically lower before the anthers dehisced and after stamens bent outwards, as well as before and after the period of stigmatic receptivity.

Conclusions

It is shown for the first time that a combination of movement herkogamy and dichogamy can maintain high pollination accuracy in flowers with generalized pollination. Staggered pollen and stigma presentation with spatial correspondence can both reduce sexual interference and improve pollination accuracy.     

Aechmea pectinata: a hummingbird-dependent bromeliad with inconspicuous flowers from the rainforest in south-eastern Brazil

The pollination biology of Aechmea pectinata (Bromeliaceae) was studied in a submontane rainforest in south-eastern Brazil. This species has a mainly clumped distribution and its aggregated individuals are likely to be clones. From October to January, during the flowering period, the distal third of its leaves becomes red. The inflorescence produces 1-15 flowers per day over a period of 20-25 d. The flowers are inconspicuous, greenish-white coloured, tubular shaped with a narrow opening, and the stigma is situated just above the anthers. Anthesis begins at 0400 h and flowers last for about 13 h. The highest nectar volume and sugar concentration occur between 0600 and 1000 h, and decrease throughout the day. Aechmea pectinata is self-incompatible and therefore pollinator-dependent. Hummingbirds are its main pollinators (about 90 % of the visits), visiting flowers mainly in the morning. There is a positive correlation between the number of hummingbird visits per inflorescence and the production of nectar, suggesting that the availability of this resource is important in attracting and maintaining visitors. The arrangement of the floral structures favours pollen deposition on the bill of the hummingbirds. Flowers in clumps promote hummingbird territoriality, and a consequence is self-pollination in a broader sense (geitonogamy) as individuals in assemblages are genetically close. However, trap-lining and intruding hummingbirds promote cross-pollination. These observations suggest that successful fruit set of A. pectinata depends on both the spatial distribution of its individuals and the interactions among hummingbirds.     

FLORAL BIOLOGY,HUMMINGBIRD POLLINATION AND FRUIT PRODUCTION OF TRUMPET CREEPER (CAMPSIS RADICANS,BIGNONIACEAE)

Trumpet creeper is self-incompatible and bears long, tubular, orange flowers from June to September. Flowering peaks rapidly, then declines and continues at low levels for several weeks. The initial burst of flowering may attract pollinators that return even during subsequent reduced flowering. Most flowers open before noon and nectar production totals 110 μl of 26% sucrose equivalents per flower, an exceptionally high production for a temperate zone plant. Production ceases within 20–30 hr of flower opening, but corollas persist for several days and may serve to attract pollinators. Effective pollination reduces the period of stigma receptivity and speeds closing of stigma lobes. Only 1–9% of flowers produced mature fruits at four sites in Illinois and Missouri. Roughly 400 pollen grains had to be deposited on a receptive stigma to cause fruit development beyond an initial period of high abortion. At two sites, 17% and 89% of stigmas received over 400 pollen grains. Assuming 50% of deposited grains were from the same plant, fruit production at one site was clearly pollinator limited, that at the second site may have been. Ruby-throated Hummingbirds (Archilochus colubris) deposited ten times as much pollen per stigma per visit as honeybees (Apis mellifera) and bumblebees (Bombus spp.). Fruit set was highest where rubythroat visitation was most frequent. Trumpet creeper appears primarily adapted for hummingbird pollination, but can also be adequately pollinated by honeybees and bumblebees. This is one of the first attempts to relate pollen-depositing capabilities of pollinators of any plant to pollen requirements for fruit production. Several characteristics suggest that trumpet creeper may be adapted to pollination at low densities (often called traplining) in its presumed original, woodland, habitat.     

大花黄牡丹的开花特性与繁育系统

2019-2020年观察河南省栾川县引种栽培的西藏特有植物大花黄牡丹(Paeonia ludlowii)开花过程和访花昆虫,计算花粉-胚珠比(P/O)和杂交指数(OCI),检测花粉活力与柱头可授性并结合人工控制授粉试验,探究其开花特性和繁育系统类型.结果表明:(1)大花黄牡丹花朵昼开夜合,花朵随花冠展开下垂,伴花冠闭合...     

Floral biology and pollination in Cucumis melo L., a tropical andromonoecious cucurbit

We studied floral biology and the role of flower visitors in fruit set of muskmelon (Cucumis melo L.). Muskmelon produced Staminate (hereafter ‘S’) and Hermaphrodite (hereafter ‘H’) flowers with a ratio of 18:1. Flowers opened around 40 days after planting and flowering continued for another 40 days. Longevity of both types of flowers was one day. Anthesis in S flowers was earlier (0545–0700 h) than that of H flowers (0700–0830 h). Anther dehiscence occurred 10–15 min after anthesis in both the flowers. The number of pollen grains in H flowers was significantly lower (2715 ± 143) than S flowers (4968 ± 398). Pollen viability and stigma receptivity was maximum between 1600 and 1800 h. The pollen tube of pollen grains from H flowers grew very slowly and never reached the ovary. There were two peaks in nectar production in a day (1000–1200 h and 1400–1800 h). Sixteen species of insects belonging to Hymenoptera (81.25%), Diptera (12.50%) and Lepidoptera (6.5%) visited muskmelon flowers. Major visitors were honeybees, Apis cerana F. and A. florea F. and both were efficient pollinators. Diversity and abundance of flower visitors positively correlated with floral abundance. In pollination exclusion experiments, no fruit set was observed in bagged, self-pollinated and the flowers artificially crossed only with other H pollen. But, those flowers hand pollinated with pollen from S flowers and ones that were allowed for open pollination set maximum fruits. The crop needs a minimum of 8–10 bee visits per flower to achieve the same level of pollination efficiency provided with natural/unrestrained visits.     

The pollination ofStenorrhynchos lanceolatus (Aublet) L. C. Rich. (Orchidaceae: Spiranthinae) by hummingbirds in southeastern Brazil

Hummingbird pollination is documented for a natural population ofStenorrhynchos lanceolatus Aublet. L. C. Rich. occurring in Rio de Janeiro State, southeastern Brazil. At the study site the plants are pollinated byPhaethornis eurynome (Phaethorninae),Thalurania glaucopis (females only) andLeucochloris albicollis (Trochilinae). The plants offer nectar as a reward and the pollinaria become stuck to the surface of the hummingbird's bill while it is probing the flowers. The orchid population received a few (0–4) hummingbird visits per day, with about 83% of the flowers being pollinated. In spite of the low frequency of visits, the granular structure of the pollinarium plus the behaviour of the most frequent pollinators, which tend to visit all the fresh-looking flowers of each inflorescence, a very high fruiting success was promoted. Experimental evidence suggests that the pollinaria may remain up to 6.30 hours on the hummingbird's bill, enhancing the chances of cross-pollination and long-distance pollen flow.