A pollinators' eye view of a shelter mimicry system

Background and Aims

‘Human-red’ flowers are traditionally considered to be rather unpopular with bees, yet some allogamous species in the section Oncocyclus (genus Iris, Iridaceae) have evolved specialized interactions with their pollinators, a narrow taxonomic range of male solitary bees. The dark-red, tubular flowers of these irises are nectarless but provide protective shelters (i.e. a non-nutritive form of reward) primarily to male solitary bees (Apidae, Eucerini) that pollinate the flowers while looking for a shelter. An earlier study on orchids suggested that species pollinated predominantly by male solitary bees produce significantly larger amounts and larger numbers of different n-alkenes (unsaturated cuticular hydrocarbons). Whether or not this also applies to the Oncocyclus irises and whether pollinators are attracted by specific colours or scents of these flowers is unknown.

Methods

Using Iris atropurpurea, recording of pollinator preferences for shelters with different spatial parameters was combined with analyses of floral colours (by spectrophotometry) and scents (by gas chromatography–mass spectrometry) to test the hypotheses that (a) pollinators significantly prefer floral tunnels facing the rising sun (floral heat-reward hypothesis), and that (b) flowers pollinated predominantly by male solitary bees produce significantly larger amounts and larger numbers of unsaturated cuticular hydrocarbons (n-alkenes) in their floral scent (preadaptation to sexual-deception hypothesis).

Key Results

Male bees do not significantly prefer shelters facing the rising sun or with the presence of high absolute/relative amounts and numbers of n-alkenes in the floral scent.

Conclusions

The results suggest that the flowers of I. atropurpurea probably evolved by pollinator-mediated selection acting primarily on floral colours to mimic large achromatic (‘bee-black’) protective shelters used preferentially by male solitary bees, and that pollinator visits are presumably not the result of an odour-based sexual stimulation or motivated by an increased morning floral heat reward in tunnels facing the rising sun.     

The endangered Iris atropurpurea (Iridaceae) in Israel: honey-bees,night-sheltering male bees and female solitary bees as pollinators

Background and Aims

The coastal plain of Israel hosts the last few remaining populations of the endemic Iris atropurpurea (Iridaceae), a Red List species of high conservation priority. The flowers offer no nectar reward. Here the role of night-sheltering male solitary bees, honey-bees and female solitary bees as pollinators of I. atropurpurea is documented.

Methods

Breeding system, floral longevity, stigma receptivity, visitation rates, pollen loads, pollen deposition and removal and fruit- and seed-set were investigated.

Key Results

The main wild pollinators of this plant are male eucerine bees, and to a lesser extent, but with the potential to transfer pollen, female solitary bees. Honey-bees were found to be frequent diurnal visitors; they removed large quantities of pollen and were as effective as male sheltering bees at pollinating this species. The low density of pollen carried by male solitary bees was attributed to grooming activities, pollen displacement when bees aggregated together in flowers and pollen depletion by honey-bees. In the population free of honey-bee hives, male bees carried significantly more pollen grains on their bodies. Results from pollen analysis and pollen deposited on stigmas suggest that inadequate pollination may be an important factor limiting fruit-set. In the presence of honey-bees, eucerine bees were low removal–low deposition pollinators, whereas honey-bees were high removal–low deposition pollinators, because they removed large amounts into corbiculae and deposited relatively little onto receptive stigmas.

Conclusions

Even though overall, both bee taxa were equally effective pollinators, we suggest that honey-bees have the potential to reduce the amount of pollen available for plant reproduction, and to reduce the amount of resources available to solitary bee communities. The results of this study have potential implications for the conservation of this highly endangered plant species if hives are permitted inside reserves, where the bulk of Oncocyclus iris species are protected.     

Pollination of Oncocyclus irises (Iris: Iridaceae) by night-sheltering male bees

Irises in the section Oncocyclus (Siems.) Baker ( IRIS: Iridaceae) grow throughout the Middle East and have large and dark-coloured flowers but no nectar reward available to flower visitors. Consequently, no reward-collecting pollinators have been observed visiting the flowers during daytime. The only visitors are solitary male bees ( Eucera spp.: Apidae) that enter the flowers at dusk and stay there overnight. Here we describe the mating system of Oncocyclus irises, and the role of night-sheltering male bees in their pollination system. Pollen viability in I. haynei on Mt. Gilboa was very high (>90%) throughout all floral life stages. Stigmas were receptive in buds and in open flowers, but not in older ones. Self-pollination yielded no fruits in three species, confirming complete self-incompatibility in Oncocyclus irises. On average, 1.9 flowers were visited by each male bee before it settled for the night in the last one. Moreover, Iris pollen was present on the dorsal side of 38.8% of males caught sheltering in flower models mounted near an I. atrofusca population, indicating that pollen is transferred between flowers by night-sheltering solitary male bees. We have surveyed 13 flowering populations of six Oncocyclus species for the presence of night-sheltering male bees as well as for fruit set. We found a positive correlation, indicating that sexual reproduction in Oncocyclus irises is dependent on night-sheltering solitary male bees. Based on their complete self-incompatibility, the absence of nectar-collecting visitors during the day, and the transfer of pollen grains by the night-sheltering solitary male bees, we conclude that fertilization of Oncocyclus irises is totally dependent on pollination by night-sheltering solitary male bees.     

Solitary and social bees as pollinators of Wahlenbergia (Campanulaceae): single-visit effectiveness, overnight sheltering and responses to flower colour

Solitary bees often form specialised mutualisms with particular plant species, while honeybees are considered to be relatively opportunistic foragers. Thus, it may be expected that solitary bees are more effective pollinators than honeybees when foraging on the same floral resource. To test this, we studied two Wahlenbergia species (Campanulaceae) in South Africa that are visited by both social honeybees and solitary bees, and which are shown here to be genetically self-incompatible and thus reliant on pollinator visits for seed production. Contrary to expectation, the solitary bee Lipotriches sp. (Halictidae) and social bee Apis mellifera (Apidae), which were the two most frequent visitors to flowers of the study species, were equally effective pollinators in terms of the consequences of single visits for fruit and seed set. Both bee species preferentially visited female phase flowers, which contain more nectar than male phase flowers. Male solitary bees of several genera frequently shelter overnight in flowers of both Wahlenbergia species, but temporal exclusion experiments showed that this behaviour makes little contribution to either seed production or pollen dispersal (estimated using a dye particle analogue). Manipulation of flower colour using a sunscreen that removed UV reflectance strongly reduced visits by both bee groups, while neither group responded to Wahlenbergia floral odour cues in choice tests. This study indicates that while flowers of Wahlenbergia cuspidata and W. krebsii are pollinated exclusively by bees, they are not under strong selection to specialise for pollination by any particular group of bees.     

Association of flower color with pollen reward may explain increased bumblebee visitation to the Scotch broom yellow morph

Given that pollinators usually visit flowers for hidden rewards, they need to rely on floral traits that indicate reward status (“honest signals”). However, the relationship between pollination, honest signals, and floral rewards is little documented in natural conditions. The Scotch broom (Cytisus scoparius) is an invasive shrub with polymorphism in the color of its flowers that can be yellow, orange, or red. In three areas dominated by the Scotch broom, we described the abundance of the floral morphs and estimated bumblebee (Bombus terrestris) visitation rate. We examined whether bumblebee visitation to the floral morphs was related to pollen reward. We collected flowers and classified their stamens according to their function: reward or pollen export. Then, we measured anther size and estimated pollen quantity. The yellow morph was more abundant and more visited by bumblebees than the orange and red morphs. The yellow flowers did indeed offer more pollen than the other morphs and this occurred only for rewarding anthers, suggesting that bumblebees could use yellow color as an honest signal to visit the most rewarding flowers. We discuss whether innate and/or learned preferences of bumblebees can explain why the yellow morph is more visited, pollinated, and abundant, while the other morphs are maintained at a lower frequency. This is one of the few field works that shows that variation in intra-specific floral traits is associated with variation in floral reward and pollinator visitation rate, helping to understand the foraging preferences of pollinators and the coexistence of floral morphs in nature.

Clinical trials registration: Not applicable.

     

Bees use honest floral signals as indicators of reward when visiting flowers

Pollinators visit flowers for rewards and should therefore have a preference for floral signals that indicate reward status, so called ‘honest signals’. We investigated honest signalling in Brassica rapa L. and its relevance for the attraction of a generalised pollinator, the bumble bee Bombus terrestris (L.). We found a positive association between reward amount (nectar sugar and pollen) and the floral scent compound phenylacetaldehyde. Bumble bees developed a preference for phenylacetaldehyde over other scent compounds after foraging on B. rapa. When foraging on artificial flowers scented with synthetic volatiles, bumble bees developed a preference for those specific compounds that honestly indicated reward status. These results show that the honesty of floral signals can play a key role in their attractiveness to pollinators. In plants, a genetic constraint, resource limitation in reward and signal production, and sanctions against cheaters may contribute to the evolution and maintenance of honest signalling.     

RELATIVE POLLINATOR EFFECTIVENESS AND EVOLUTION OF FLORAL TRAITS IN SPATHIPHYLLUM FRIEDRICHSTHALII (ARACEAE)

We studied the relative effectiveness of different pollinators of Spathiphyllum friedrichsthalii Schott for 15 months on Barro Colorado Island, Panama. Pollen-foraging stingless bees (Apidae: Trigona) made 87% of floral visits. Experiments showed that these bees pollinate flowers, and correlations of fruit- and seed-set with visitation frequencies and floral contact times suggested that they were responsible for the majority of seeds produced. Fifteen species of fragrance-foraging, male euglossine bees (Apidae: Euglossini) collectively accounted for a small portion of seed-set in fewer than 27% of the inflorescences. Neocorynura (Halictidae) were pollen thieves and were unimportant as pollinators. We propose that euglossine and stingless bees differentially influence outcrossing rates and the evolution of floral traits of S. friedrichsthalii. Foraging behavior of male euglossines should allow for more long-distance pollen flow whereas stingless bees are likely to promote near-neighbor and geitonogamous pollinations. We discuss why the prolonged male phase of anthesis in this protogynous species may be maintained through pollination by stingless bees rather than male euglossines. Furthermore, although the floral fragrance is attractive to many species of male euglossines, it attracts few individuals. This condition may represent an intermediate step in the evolution of predominant pollination by male euglossines.     

Flower biology of the cactus Coryphantha elephantidens in the tropical dry forest of Central Mexico

Floral traits and sexual systems in angiosperms are strategies that enhance outcrossing within hermaphrodite flowers and among individuals in a population. Sexual systems with unisexual flowers have also evolved among angiosperms, resulting in sex specialization. Furthermore, the interaction of floral traits and floral visitors determines successful plant reproduction. Globose cacti are bee pollinated, and variation in the diversity of their pollinator assemblages is strongly associated with floral phenotype. Our objective was to describe the floral biology of the cactus Coryphantha elephantidens and to determine its relationship with pollinators. Floral traits were studied by direct observations in live and fixed flowers. The breeding system was determined using two estimators based on floral morphology: pollen grains to ovules per flower (P/O) ratio and outcrossing index. Pollination treatments were conducted to determine the mating system. Floral visitors were recorded using direct observation. Flowers of C. elephantidens are variable in color, protandric, herkogamous and nectarless. Estimators of the breeding system indicated xenogamy, which is consistent with the obligate outcrossing revealed by the pollination experiment. Thirty-seven percent of the plants have female flowers that do not produce pollen, making this population functionally gynodioecious. Both fruit and seed set were high compared to other globose cacti. Pollinators included eight species of native bees, a more diverse pollinator assemblage than other globose cacti. Given the high pressure on pollen due to functional gynodioecy, nectarless flowers, an outcrossing mating system, and the necessity of pollinators to set seeds, we concluded that native bees are highly efficient pollinators that play a crucial role in the sexual reproduction of C. elephantidens.     

Floral sexual dimorphism and flower choice by pollinators in a nectarless monoecious vine Akebia quinata (Lardizabalaceae)

We investigated the pollination system and movement patterns of pollinators among flowers of the nectarless, monoecious vine Akebia quinata in natural populations and experimental floral arrays. Female flowers did not offer any rewards for pollinators and were larger than male flowers. Pollinators of A.quinata , such as small solitary bees and hoverflies, clearly discriminated between male and female flowers. Hoverflies always visited male flowers and rarely visited female flowers. In contrast, solitary bees tended to visit female flowers first when entering the array, but then switched to male flowers within the same foraging bout. This tendency disappeared when the sepal size of female flowers was experimentally reduced to the size of male flowers. Thus, observed non-randomness in flower choice by solitary bees may be caused by female>male sexual dimorphism and may increase the chance of cross-pollination and lower the probability of geitonogamous pollination in a single visit to a plant. Therefore, floral sexual dimorphism in A.quinata is considered to be an adaptation for deceptive pollination associated with discriminating pollinators.     

Pollination of Campomanesia phaea (Myrtaceae) by night‐active bees: a new nocturnal pollination system mediated by floral scent

• Bees are the most important diurnal pollinators of angiosperms. In several groups of bees a nocturnal/crepuscular habit developed, yet little is known about their role in pollination and whether some plants are adapted specifically to these bees. We used a multidisciplinary approach to investigate the reproductive biology and to understand the role of nocturnal/crepuscular bees in pollination of Campomanesia phaea (Myrtaceae), popularly named cambuci.
• We studied the floral biology and breeding system of C. phaea. We collected the floral visitors and tested the pollinators' effectiveness. We also determined the floral scents released at night and during daytime, and studied behavioural responses of crepuscular/nocturnal bees towards these scents.
• The flowers of cambuci were self‐incompatible and had pollen as the only resource for flower visitors. Anthesis lasted around 14 h, beginning at 04:30 h at night. The flowers released 14 volatile compounds, mainly aliphatic and aromatic compounds. We collected 52 species of floral visitors, mainly bees. Nocturnal and crepuscular bees (four species) were among the most frequent species and the only effective pollinators. In field bioassays performed at night, nocturnal/crepuscular bees were attracted by a synthetic scent blend consisting of the six most abundant compounds.
• This study describes the first scent‐mediated pollination system between a plant and its nocturnal bee pollinators. Further, C. phaea has several floral traits that do not allow classification into other nocturnal pollination syndromes (e.g. pollinator attraction already before sunrise, with pollen as the only reward), instead it is a plant specifically adapted to nocturnal bees.

     

Floral reward presentation favored the expression of male function in the pollen‐only flower Melastoma malabathricum

Abstract Animal‐pollinated plant species modulate the presentation of pollinator rewards to maximize reproductive success. In plants providing pollen as the only reward for pollinators, it is usually difficult to unravel the dual roles of reward presentation and the realization of male and female functions (pollen removal and deposition). Exploiting the two types of anther in the androecia of Melastoma malabathricum L., we examined whether the removal of pollen for reward is regulated primarily to favor male function or female function. Pollen removal by carpenter bees from the feeding and pollination anthers, as well as pollen deposition on the stigmas, were quantified during anthesis of M. malabathricum. There was no significant difference in pollen removal rates from the feeding and pollination anthers of M. malabathricum between the onset of anthesis and flower wilting. The stigmatic pollen loads exceeded the ovule number after three sonication bouts, and female function was satisfied earlier than male function. The results support the hypothesis that the presentation of pollination reward in this species is regulated primarily to favor the expression of male function, rather than female function, in agreement with the pollen‐donation hypothesis. A cooperative relationship between the feeding and pollination anthers was demonstrated in heterantherous flowers, which optimizes the balance in investments between pollinator rewards and “functional pollen” for gene transfer.     

Pollination ofEchinocereus fasciculatus andFerocactus wislizenii

One of the most common types of cactus flower in the southwestern United States is the large, colorful, cup-shaped flower.Echinocereus fasciculatus var.boyce-thompsonii in Arizona is a representative of this class of flowers. Its flowers are visited by three common types of insect visitors: medium-sized bees, small solitary bees, and beetles. All three types of visitors come into contact with the pollen, but only the mediumsized bees regularly touch the stigma in their visitations. The main effective pollinators are therefore the medium-sized bees (Megachile, etc.).Ferocactus wislizenii has a similar floral mechanism and is likewise pollinated mainly by medium-sized bees (Megachile, Lithurge, Diadasia, etc.).Pollination of North American Cacti, 1.     

Change of floral orientation affects pollinator diversity and their relative importance in an alpine plant with generalized pollination system,Geranium refractum (Geraniaceae)

Floral orientation may affect pollinator attraction and pollination effectiveness, and its influences may differ among pollinator species. We, therefore, hypothesized that, for plant species with a generalized pollination system, changes in floral orientation would affect the composition of pollinators and their relative contribution to pollination. Geranium refractum, an alpine plant with downward floral orientation was used in this study. We created upward-facing flowers by altering the flower angle. We compared the pollinator diversity, pollination effectiveness, and pollinator importance, as well as female reproductive success between flowers with downward- and upward-facing orientation. Results indicated that the upward-facing flowers were visited by a wider spectrum of pollinators (classified into functional groups), with higher pollinator diversity than natural flowers. Moreover, due to influences on visitation number and pollen removal, the pollinator importance exhibited by the main pollinator groups differed between flower types. Compared with natural flowers, the pollination contribution of principal pollinators (i.e., bumblebees) decreased in upward-facing flowers and other infrequent pollinators, such as solitary bees and muscoid flies, removed more pollen. Consequently, stigmatic pollen loads were lower in upward- than in downward-facing flowers. These findings reveal that floral orientation may affect the level of generalization of a pollination system and the relative importance of diverse pollinators. In this species, the natural downward-facing floral orientation may increase pollen transfer by effective pollinators and reduce interference by inferior pollinators.     

Errata

In south-eastern Arizona, heterostylous (often trimorphic) populations of Oxalis alpina (Rose) Knuth are visited most commonly by females of the solitary bee Heterosarus bakeri Cockerell. Bees collect pollen from flowers and are presumed to be the major pollinators of O. alpina in this region. Analysis of pollen loads from the corbiculae of H. bakeri suggests that individual bees may specialize temporally on different floral forms. However, the apparent preferential collection of pollen probably results from spatial segregation of morphs and the localized foraging behaviour of bees rather than preference on the part of individual bees for particular stylar forms. As a group, bees appear to visit floral morphs of O. alpina indiscriminately, even though individual bees may have a preponderance of pollen from one morph type. Despite spatial segregation leading to pollinator flights between members of the same incompatibility group, capsule and seed production in populations of O. alpina is high for all forms. Loss of the mid form in some populations cannot be attributed to pollinator preferences for individual style morphs.     

Dioecious <Emphasis Type="Italic">Clusia nemorosa</Emphasis> achieves pollination by combining specialized and generalized floral rewards

Plants often combine multiple strategies to achieve pollen transfer. The dioecious Clusia nemorosa (Clusiaceae) produces floral resin, a specialized reward for resin-collecting bees. It also exhibits floral automimicry with female flowers mimicking male flowers in order to attract pollen-collecting insects. We observed the hourly visitation frequency and behaviour of bee visitors on two rock savanna sites in French Guiana. The major strategy in pollen transfer and the variation in visitation rates among visitor species were examined. We hypothesized that the visitation rate will vary between the floral sexes and degree of this variation will differ between the two-reward systems. We found no evidence for visits being exclusively related to resin collection, which we expected to be the principal strategy in pollen transfer. Deceit pollination appeared to have minor importance and seemed to be locally associated with the site, where demand for pollen was greater. Flower visits that probably facilitated most pollen transfer, combined resin and pollen. The pollinators involved in this system collected pollen from male flowers and resin from female flowers. The fruit set was not particularly low (44.19%) so offering different rewards by different flower genders has not constrained reproductive success in this system. Pronounced variation in visitation rates between sexes was not related to the pollination mechanisms but to the demand for the two rewards. Overall demand for pollen was greater than demand for resin. Female flowers were visited much less frequently than male flowers. Peak pollen collection occurred in the morning, i.e., as soon as the resource was available, while resin was collected throughout the day. There was a local variability in demand for the two resources because both the visitation rate and the behaviour of foraging bees varied between the two observation sites.     

Optimal foraging: Random movement by pollen collecting bumblebees

Summary Two bumblebee species, Bombus bifarius and B. flavifrons, forage randomly with respect to direction when gathering pollen on Potentilla gracilis. Bees avoid revisiting flowers by being able to differentiate recently visited from unvisited flowers. This recognition occurs while bees are flying over open flowers and appears to be a response to the amount of available pollen within flowers. Random foraging with respect to direction is the optimal strategy when the probability of flower revisitation is low. Bumblebees appear to be moving preferentially between nearest neighbors, again as predicted by foraging theory. This behavior causes the establishment of pollen patches in the P. gracilis population. Unlike other pollinators studied in similar situations, bumblebees on P. gracilis do not forage utilizing an area-restricted searching behavior. Because floral reward quality can be assessed at low cost by bees foraging on P. gracilis, their tendency to move to nearby flowers even after encountering a poor quality blossom apparently yields a higher rate of net energy intake than does area-restricted searching. The data indicate that bumblebees exhibit great plasticity in foraging behavior and that they are able to forage efficiently under a wide range of environmental conditions.     

Interaction between oil-collecting bees and seven species of Plantaginaceae

Oil-bee/oil-flower mutualism evolved through multiple gains and losses of the ability to produce floral oil in plants and to collect it in bees. Around 2000 plant species are known to produce floral oils that are collected by roughly 450 bee species, which use them for the construction of nests and for the larval food. The Plantaginaceae contain several Neotropical species that produce floral oils, the main reward offered by these plants. In the genera Angelonia, Basistemon, Monopera and Monttea, mainly associated with Centris bees, the floral oil is produced in trichomes that are located in the inner corolla. The pollinators of a few species in this neotropical clade of Plantaginaceae are known, and the role of flower morphology as well as the requirements from pollinators and the role of other groups of bees in the pollination of these flowers remains unclear. In this paper we provide a list of the flower visitors of seven Plantaginaceae species (six Angelonia species and Basistemon silvaticus) analyzing their behavior to highlight the legitimate pollinators and illustrating little known aspects of flower morphology and oil-collecting apparatuses of the bees. Two general morphological patterns were observed in the Angelonia flowers: deep corolla tube with short lobes, and short corolla tube with long lobes. Corolla tubes of different length result in pollen adherence to different parts of the insect body. The six Angelonia species and B. silvaticus flowers were visited by 25 oil-collecting bee species (10 Centris, 11 Tapinotaspidini and 4 Tetrapedia species), the majority acting as legitimate visitors. The flowers were also visited by illegitimate bee pollinators, which collected pollen but do not transfer it to the female organ. Specialized collectors of Plantaginaceae floral oils present modifications on the first pair of legs, mainly in the basitarsi but also extended to the tarsomeres. The new records of Tapinotaspidini and Centridini species acting as specialized pollinators of Plantaginaceae suggest that there is a geographic variation in the pollinators of the same plant species, and that the evolutionary scenario of the historical relationships between oil-collecting bees and floral oil producing plants is more complex than previously considered.     

Reward partitioning in Capparis spp. along ecological gradient

Summary The genus Capparis is represented in Israel by three taxons of the section spinosa. The pollinators of the three taxa are hawkmoths, crepuscular bees of the genus Proxylocopa and various daily bees. However, the efficiency of the different pollinators is very varied with respect to the individual taxons. Hawkmoths were frequently observed as pollinators of C. spinosa var. aravensis and C. ovata, but rarely on C. spinosa var. aegyptia. All the other bees, on the other hand, were found abundantly on all three taxons, all over the country. The three taxa all provide different rewards for their particular pollinators. Bees visiting C. spinosa var. aegyptia are provided with a lot of pollen but a relatively small amount of nectar, with a low sugar content. C. spinosa var. aravensis and C. ovata (the flowers visited more by hawkmoths), have less pollen but a higher amount of nectar which has a higher concentration of sugar. In drier habitats the emphasis of the reward provided by the flowers is nectar, whilst in the Mediterranean habitats it is the pollen which is the reward, without any connection to the systematic origin of the plant.     

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 (~0.09 μl·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.

     

宁夏枸杞的花粉呈现式样及交配系统研究北大核心CSCD

被子植物的花回馈、雌雄蕊时空分离特征和花粉呈现式样等花部特征及传粉者效率会影响雄性适合度和有性繁殖过程。宁夏枸杞(Lycium barbarum)是中国宁夏、新疆、内蒙等干旱和半干旱地区分布的特有种。该研究对新疆喀什地区宁夏枸杞自然种群的花部综合征、花粉呈现式样、花回馈、传粉者行为与交配方式的关系进行观察及统计分析,以探讨其花粉逐步呈现的适应性及其在提高雌雄繁殖过程中的意义。结果表明:(1)宁夏枸杞的单花寿命为(4.07±0.15) d,而雄性持续时间(0.07±0.01 d)比雌性持续时间短(4±0.01 d);花寿命内雌蕊长度比雄蕊长,属柱头探出式异位类型;花粉呈现式样为不完全逐步呈现。(2)花寿命不同阶段花回馈间存在显著差异。(3)意大利蜜蜂(Apis mellifera)、熊蜂(Bombus sp.)、食蚜蝇(Syrphidae sp.)是宁夏枸杞在自然居群的主要访花者,其中熊蜂和食蚜蝇是主要传粉者,但传粉者效率低,属于高移出低沉积类型。(4)宁夏枸杞的花粉胚珠比(2 448.11±448.32)及授粉实验结果均表现出兼性异交特征;自发自交及人工自花授粉花的座果率及结籽率很低,属于自交不亲和类型;自然传粉花的座果率及结籽率比人工去雄异花低,存在其较高的花粉限制(40.71%)。研究发现,宁夏枸杞花部综合征表现出雌雄异位和花粉不完全逐步呈现式样,这是避免雌雄功能及雄蕊各花药间的干扰、减少花粉同步移出及保障其雄性适合度的有效途径,但自然居群的传粉者种类限制、传粉效率低以及自交不亲性是导致宁夏枸杞花粉限制及降低雌性繁殖成功的主要原因。