Pollination biology and reproductive success in four Brazilian species of Gomesa (Orchidaceae: Oncidiinae): Specific pollinators,but high pollen loss and low fruit set

Four species of Gomesa (Gomesa flexuosa, Gomesa ranifera, Gomesa cornigera, and Gomesa riograndensis), a horticulturally important, albeit scarcely studied orchid genus, were investigated. Pollination biology was studied through fieldwork in Rio Grande do Sul in Southern Brazil during two flowering seasons. Breeding systems were studied through controlled pollinations in cultivated plants. All studied species secrete floral oils through elaiophores and are exclusively pollinated by native, oil-collecting bees of the Centridini or Tapinotaspidini tribes. Pollinarium reconfiguration after withdrawal, a feature likely promoting cross-pollination, was recorded in G. cornigera and G. riograndensis. All studied species are pollinator-dependent and either predominantly or fully self-incompatible, that is, unable to set fruit following self-pollination. The used indexes of pollination efficiency consistently scored values below 1, indicating that in all studied species less than one flower is pollinated per pollinarium removed. Accordingly, pollen loss was high, ranging from 40% to 75%. Furthermore, inflorescences in natural populations displayed low fruit sets (below 13%). Gomesa flexuosa presented the highest values of pollinarium removal (36.24%) and deposition (15.34%). Significantly, this is the only studied species bearing a tabula infraestigmatica, a column swelling that bees hold to stabilize themselves while gathering the floral oils. Since pollinators were observed in all studied species spending considerable time (up to 3 min 46 s) and visiting several (up to 19) flowers, we propose that the observed low fruit set is the result of a combination of self-incompatibility, pollinator-mediated self-pollination, and pollen loss.     

Pollination biology of Cymbidium goeringii (Orchidaceae) in China

The genus Cymbidium comprises three subgenera with ca. 50 species. Interactions between pollinators and plants have been studied in the two subgenera Cymbidium and Cyperorchis, but only a few studies in the subgenus Jensoa have been reported. Here we report on the reproductive characteristics of C. goeringii (in sub-genus Jensoa) in three populations in the southwest of Hunan Province, China, during the winter from December 2005 to March 2006. Floral phenological and morphological features, behavior of visitors, the breeding system, and fruit sets under natural conditions were studied. The flowers of C. goeringii were strongly fragrant, but did not present any rewards to the visitors. The flowering period of C. goeringii in the studied populations lasted about 40 days, and most flowers (about 60%) opened within 30 days. Flowers opened immediately when temperature increased obviously and reached to about 16 ℃. The flowering time of the pollinated flowers, unpollinated flow-ers and the flowers with pollinarium removed were similar. Two bees of Apidae, Apis cerana cerana (honeybee) and Anthophora melanognatha, were observed visiting flowers of C. goeringii, but only the honeybees performed as pollinators. The honeybees mostly visited the orchid flowers at 10:00–17:00 on sunny days with temperature above 10 ℃. A total of only thirteen visits were observed during 20 days of observation, indicating pollinators were rare. Honeybees directly landed on the upper surface of the labellum and inserted their heads into the flowers between column and labellum, while the hind legs trod on the surface of the curved downward mid-lobe of label-lum. When a honeybee landed on the labellum of a flower, the labellum moved up and down slightly. After the honeybee entered the flower further, its head might touch the foot of the column. At this time, the body of the honeybee was parallel with the upper surface of the labellum. Then the honeybee used its front legs to scratch on the callus ridges on the upper surface of the labellum, and its hind legs hooked the edges of the side lobe of label-lum, trying to exit forcibly from the flower. During exiting process, sometimes the honeybee’s body was arched owing to tension. In this case, the surface of the scutellum came into close contact with the viscidium and then pollinaria, together with the anther cap, were removed. When this honeybee visited next flower, the pollinaria would be adhered to the stigma when it arched its body during the exiting process. Three plant species flowered synchronously with C. goeringii in the studied areas, but their flowers were different with C. goeringii in color or shape. Because C. goeringii is rewardless to pollinators, the flowers probably attract visitors by olfactory stimu-lus. Breeding system experiments showed no spontaneous autogamy and pollination success relying on pollinators in C. goeringii. Artificial pollination resulted in 90% fruit set by induced autogamy, 100% by pollinating within clone, and 100% by xenogamous pollination, respectively. These results indicate that C. goeringii is highly self-compatible and the fruit production is pollen limited. Because pollinators are essential for fruit set of C. goeringii in natural habitats, protection of wild honeybee populations or apiculture is likely a simple but effective strategy to maintain the orchid populations.     

Multiple paternity in an aggregate breeding amphibian: the effect of reproductive skew on estimates of male reproductive success

Aggregate, or explosive, breeding is widespread among vertebrates and likely increases the probability of multiple paternity. We assessed paternity in seven field-collected clutches of the explosively breeding spotted salamander (Ambystoma maculatum) using 10 microsatellite loci to determine the frequency of multiple paternity and the number of males contributing to a female's clutch. Using the Minimum Method of allele counts, multiple paternity was evident in 70% of these egg masses. Simple allele counts underestimate the number of contributing males because this method cannot distinguish multiple fathers with common or similar alleles. Therefore, we used computer simulations to estimate from the offspring genotypes the most likely number of contributing fathers given the distributions of allele frequencies in this population. We determined that two to eight males may contribute to A. maculatum clutches; therefore, multiple paternity is a common strategy in this aggregate breeding species. In aggregate mating systems competition for mates can be intense, thus differential reproductive success (reproductive skew) among males contributing to a female's clutch could be a probable outcome. We use our data to evaluate the potential effect of reproductive skew on estimates of the number of contributing males. We simulated varying scenarios of differential male reproductive success, ranging from equal contribution to high reproductive skew among contributing sires in multiply sired clutches. Our data suggest that even intermediate levels of reproductive skew decrease confidence substantially in estimates of the number of contributing sires when parental genotypes are unknown.     

Reproductive biology of Dyckia excelsa Leme (Bromeliaceae): a xerophyte species from ironstone outcrops in central-western Brazil

Dyckia is the third most diverse genus from Pitcairnoideae, pollinated mainly by insects and hummingbirds. In this study, we evaluated demography, reproductive biology and pollination of Dyckia excelsa, a saxicolous species typical of ironstone outcrops. It occurs in groupings composed of genets, ramets and seedlings and bloomed several times, principally in September, with fruiting and dispersing of seeds in November. The anthesis is diurnal and flowers remain open for 2 days. Nectar volume decreased during the anthesis, whereas nectar sugar concentration remained constant. Dyckia excelsa is partially self-compatible and xenogamic; the highest fruit set was observed in the control and cross-pollination treatments; high seed germination rates were observed in all treatments. Flowers have the ornithophilous syndrome, but hummingbirds, bees and butterflies visited them. The occurrence of groupings with multiple inflorescences could contribute to geitonogamy. The high number of flowers during a year supplies food resources and ensures the fidelity of pollinators.     

广东地区外来种五爪金龙的传粉生物学研究（英文）

五爪金龙(Ipomoea cairica)是一种匍匐或攀援生长的入侵杂草。2006-2007年作者在广东地区开展了对该入侵种的传粉生物学研究。五爪金龙在广东全年均可开花,花序为聚伞花序,花冠为紫色或蓝紫色喇叭状。开花时间在早晨4:30-5:20之间,下午17:40闭合,持续大约12h。每朵花平均分泌花蜜量为5.82±2.47μL(n=10),花蜜平均含糖量为41.03±6.52%,氨基酸含量为0.042mg/mL。开花过程中花粉活性和柱头可受性均保持较高水平(>90%)。花粉/胚珠比率(P/O)为4,778.18±264.58(n=10)。木蜂(Xylocopasp.)是其有效的传粉昆虫,蝇类和蝶类为随机访问者。开花过程中柱头与花药相接触,有利于自花授粉。然而,繁育系统的研究表明五爪金龙是自交不亲和植物,其种子仅能通过异花授粉获得。     

The reproductive biology of Stellera chamaejasme (Thymelaeaceae): A self-incompatible weed with specialized flowers

It has profound implications for species invasions and fitness, how weeds achieve reproductive success. We present the first study on the reproductive biology of Stellera chamaejasme, a toxic perennial weed which is abundant in the alpine meadows on the eastern Tibetan Plateau of China since the 1960s. S. chamaejasme has synchronogamy and herkogamous flowers, which last for about 11 days. Flowers can be yellow, white or reddish. Our results suggest that this species is self-incompatible and depends entirely on pollen vectors for seed production. All the pollinators observed were Lepidopteran species; however, the pollinator assemblage was significantly different among populations and likely independent on floral colour. Reproductive success and invasion of the weed might be a complex function of floral traits, breeding system and pollination ecology. Generally, plants with generalized pollination system are more invasive. However, our results suggest that specialized flowers and self-incompatibility in the present case may not prevent invasion of the weed.     

Pollination biology of Eulophia alta (Orchidaceae) in Amazonia: effects of pollinator composition on reproductive success in different populations

Background and Aims

Spatial variation in pollinator composition and abundance is a well-recognized phenomenon. However, a weakness of many studies claiming specificity of plant–pollinator interactions is that they are often restricted to a single locality. The aim of the present study was to investigate pollinator effectiveness of the different flower visitors to the terrestrial orchid Eulophia alta at three different localities and to analyse whether differences in pollinator abundance and composition effect this plant''s reproductive success.

Methods

Natural pollination was observed in vivo, and manipulative experiments were used to study the pollination biology and breeding system of E. alta at three sites near Manaus, Brazil. To gain a better understanding of the underlying mechanisms of pollinator attraction, nectar composition and secretion patterns were also studied, floral scent composition was analysed and a bioassay was conducted.

Key Results

Flower visitors, pollinator composition, pollinia transfer efficiency of particular pollinator species and natural fruit set differed among the investigated populations of E. alta. Flowers were self-compatible, partially autogamous and effectively pollinated by five bee species (four Centris species and Xylocopa muscaria). Visiting insects appeared to imbibe small amounts of hexose-rich nectar. Nectar sugar content was highest on the third day after flower opening. Floral fragrance analyses revealed 42 compounds, of which monoterpenes and benzenoids predominated. A bioassay using floral parts revealed that only floral tissue from the labellum chamber and labellum tip was attractive to flower visitors.

Conclusions

The data suggest that observed differences in reproductive success in the three populations cannot be explained by absolute abundance of pollinators alone. Due to behavioural patterns such as disturbance of effective pollinators on flowers by male Centris varia bees defending territory, pollinia transfer efficiencies of particular pollinator species also vary between study sites and result in differing reproductive success.     

广东地区外来种五爪金龙的传粉生物学研究

五爪金龙(Ipomoea cairica)是一种匍匐或攀援生长的入侵杂草。2006–2007年作者在广东地区开展了对该入侵种的传粉生物学研究。五爪金龙在广东全年均可开花, 花序为聚伞花序, 花冠为紫色或蓝紫色喇叭状。开花时间在早晨4: 30–5: 20之间, 下午17: 40闭合, 持续大约12 h。每朵花平均分泌花蜜量为5.82 ± 2.47 μL (n = 10), 花蜜平均含糖量为41.03 ± 6.52%, 氨基酸含量为0.042 mg/mL。开花过程中花粉活性和柱头可受性均保持较高水平(>90%)。花粉/胚珠比率(P/O)为4,778.18 ± 264.58 (n = 10)。木蜂(Xylocopa sp.)是其有效的传粉昆虫, 蝇类和蝶类为随机访问者。开花过程中柱头与花药相接触, 有利于自花授粉。然而, 繁育系统的研究表明五爪金龙是自交不亲和植物, 其种子仅能通过异花授粉获得。     

Evolution of the selfing syndrome: Anther orientation and herkogamy together determine reproductive assurance in a self‐compatible plant

Capacity for autonomous self‐fertilization provides reproductive assurance, has evolved repeatedly in the plant kingdom, and typically involves several changes in flower morphology and development (the selfing syndrome). Yet, the relative importance of different traits and trait combinations for efficient selfing and reproductive success in pollinator‐poor environments is poorly known. In a series of experiments, we tested the importance of anther–stigma distance and the less studied trait anther orientation for efficiency of selfing in the perennial herb Arabis alpina. Variation in flower morphology among eight self‐compatible European populations was correlated with efficiency of self‐pollination and with pollen limitation in a common‐garden experiment. To examine whether anther–stigma distance and anther orientation are subject to directional and/or correlational selection, and whether this is because these traits affect pollination success, we planted a segregating F2 population at two native field sites. Selection strongly favored a combination of introrse anthers and reduced anther–stigma distance at a site where pollinator activity was low, and supplemental hand‐pollination demonstrated that this was largely because of their effect on securing self‐pollination. The results suggest that concurrent shifts in more than one trait can be crucial for the evolution of efficient self‐pollination and reproductive assurance in pollinator‐poor habitats.     

Pollination biology of two columnar cacti (Neobuxbaumia mezcalaensis and Neobuxbaumia macrocephala) in the Tehuacan Valley,central Mexico

We document the pollination biology and mating systems of Neobuxbaumia mezcalaensis and Neobuxbaumia macrocephala, two Mexican giant columnar cacti. These two species form mixed forests in the western Tehuacan Valley, Mexico. The flowers of both N. mezcalaensis and N. macrocephala exhibit nocturnal anthesis, are self-incompatible, and are pollinated primarily by three species of nectar-feeding bats (Choeronycteris mexicana, Leptonycteris curasoae, and Leptonycteris nivalis). Neobuxbaumia mezcalaensis is androdioecious, a breeding system that appears to be uncommon among Cactaceae. Neobuxbaumia macrocephala is hermaphroditic. We hypothesize that columnar cacti show a geographical dichotomy in floral biology specialization that probably can be related to predictability in pollinator abundance.     

Pollination and reproductive biology of twelve species of neotropical Malpighiaceae: stigma morphology and its implications for the breeding system

BACKGROUND AND AIMS: This study on reproductive biology examines the stigmatic morphology of 12 Brazilian Malpighiaceae species with regard to their pollination and breeding system. METHODS: The species were studied in natural populations of a semi-deciduous forest fragment. Style tips were processed for observation by SEM and pollen-tube growth was analyzed under fluorescence microscopy. The breeding system was investigated by isolating flowers within waterproof bags. Floral visitors were recorded through notes and photographs. KEY RESULTS: Flowers are yellow, pink or white, protogynous, herkogamous and sometimes lack oil glands. While Banisteriopsis pubipetala has functional female flowers (with indehiscent anthers), 11 species present hermaphrodite flowers. Stigmas of these species may be terminal, with a slightly concave surface, or internal, consisting of a circular cavity with a large orifice, and are covered with a thin, impermeable cuticle that prevents pollen from adhering, hydrating, or germinating. Malpighiaceae have a special type of 'wet' stigma, where a secretion accumulates under the cuticle and is released by mechanical means-mainly rupture by pollinators. Even though six species show a certain degree of self-compatibility, four of them present a form of late-acting self-incompatibility, and the individual of B. pubipetala is agamospermous. Species of Centris, Epicharis and Monoeca bees pollinate these flowers, mainly collecting oil. Some Epicharis and Monoeca species collected pollen by vibration. Paratetrapedia and Tetrapedia bees are pollen and oil thieves. CONCLUSIONS: The Malpiguiaceae species studied are pollinator-dependent, as spontaneous self-pollination is limited by herkogamy, protogyny and the stigmatic cuticle. Both the oil- and pollen-collecting behaviours of the pollinators favour the rupture of the stigmatic cuticle and the deposition of pollen on or inside the stigmas. As fruit-set rates in natural conditions are low, population fragmentation may have limited the sexual reproduction of these species.     

Pollination of Schisandra henryi (Schisandraceae) by female, pollen-eating Megommata species (Cecidomyiidae, Diptera) in south-central China

BACKGROUND AND AIMS: The mutualistic interaction between insects and flowers is considered to be a major factor in the early evolution of flowering plants. The Schisandraceae were, until now, the only family in the ANITA group lacking information on pollination biology in natural ecosystems. Thus, the objective of this research was to document the pollination biology and breeding system of Schisandra henryi. METHODS: Field observations were conducted in three populations of S. henryi and the floral phenology, floral characters and insect activities were recorded. Floral fragrances were sampled in the field and analysed using TCT-GC-MS. Floral thermogenesis was measured with a TR-71U Thermo Recorder. Pollen loads and location of pollen grains on insect bodies (including the gut) were checked with a scanning electron microscope and under a light microscope. KEY RESULTS: Schisandra henryi is strictly dioecious. Male flowers are similar to female flowers in colour, shape, and size, but more abundant than female flowers. The distance between tepals and the androecium or gynoecium is narrow. Neither male nor female flowers are fragrant or thermogenic. Schisandra henryi is pollinated only by adult female Megommata sp. (Cecidomyiidae, Diptera) that eat the pollen grains as extra nutrition for ovary maturation and ovipositing. Both male and female flowers attract the pollinators using similar visual cues and thus the female flowers use deceit as they offer no food. CONCLUSIONS: Schisandra henryi exhibits a specialized pollination system, which differs from the generalized pollination system documented in other ANITA members. Pollen is the sole food resource for Megommata sp. and the female flowers of S. henryi attract pollinators by deceit. This is the first report of predacious gall midges utilizing pollen grains as a food source. The lack of floral thermogenesis and floral odours further enforces the visual cues by reducing attractants for other potential pollinators.     

传粉昆虫对我国中南地区油茶结实和结籽的作用

油茶(Camellia oleifera)是一种重要的木本油料植物。2007-2008年在我国中南地区湖南省对油茶开展传粉生物学研究结果表明:油茶花期从10月到翌年1月份,单株开花时间一般持续20d左右,单花花期为4-5d。单花花蜜量平均为(145.40±24.89)μL,含糖量为(23.13±1.03)%,并含有17种氨基酸,约占花蜜总量的1.73%。膜翅目蜜蜂总科(Hymenoptera:Apoidea)油茶地蜂(Andrena camellia)和大分舌蜂(Colletes gigas)是油茶的有效传粉昆虫,大分舌蜂的传粉效率较油茶地蜂高;蝇类和蝶类为随机访问者。油茶不存在无融合生殖和自动自花授粉现象,其结实和结籽依赖传粉者。此外,油茶具有一定程度的自交不亲和,自交和异交的繁殖成功率存在显著性差异。人工异花授粉结果显示油茶在资源限制程度较低时,即大年时,花粉限制主要表现在结籽水平,而不是结实水平。根据油茶的传粉综合特征以及油茶在山茶属中的系统位置,目前很难解释油茶类似鸟类传粉综合特征的花蜜特征是如何演化的。     

On the low reproductive success of two Cyrtopodium species (Orchidaceae: Cyrtopodiinae): The relative roles of biotic and abiotic pollination

Rewardless orchid species are pollinated by deception and have reduced reproductive success. Those species that present self-compatibility followed by alternative mechanisms of autogamy may compensate for such episodic allogamy events. This is the case for rain-assisted self-pollination, a rare mechanism in Orchidaceae. In this study, we investigated the reproductive biology of two terrestrial species: Cyrtopodium hatschbachii and C. paludicolum. We studied their reproductive systems, examined pollinators and male and female successes, and ascertained if rain promotes self-pollination. Both species are allogamous but self-compatible. However, natural fruit set is low, not exceeding 1.40% during 4 years of observation. This may result from the reduced frequency of pollinator visitation followed by a high pollinator specificity, because each species was pollinated by a single specialist bee. Although spontaneous selfing did not occur, we verified fruits formed by rain action. The evaporation of the water droplet that accumulates on stigma helps the pollinarium to slip back, promoting selfing. This occurred in approximately 10% of C. hatschbachii fruits, but in C. paludicolum it was recorded only once during three observation years. This indicates that the phenomenon happens at random and may vary temporally. Nevertheless, rain may confer additional fruit set, especially under circumstances of pollinator limitation. Overall, we confirmed deception as a strategy for this understudied genus. In addition, we report a further two cases of rain-assisted self-pollination for Cyrtopodium, for species from the center of diversity of the genus, indicating that it may be more widespread than previously thought.     

Effects of floral display size on male and female reproductive success in Mimulus ringens

Background and Aims

The number of flowers blooming simultaneously on a plant may have profound consequences for reproductive success. Large floral displays often attract more pollinator visits, increasing outcross pollen receipt. However, pollinators frequently probe more flowers in sequence on large displays, potentially increasing self-pollination and reducing pollen export per flower. To better understand how floral display size influences male and female fitness, we manipulated display phenotypes and then used paternity analysis to quantify siring success and selfing rates.

Methods

To facilitate unambiguous assignment of paternity, we established four replicate (cloned) arrays of Mimulus ringens, each consisting of genets with unique combinations of homozygous marker genotypes. In each array, we trimmed displays to two, four, eight or 16 flowers. When fruits ripened, we counted the number of seeds per fruit and assigned paternity to 1935 progeny.

Key Results

Siring success per flower declined sharply with increasing display size, while female success per flower did not vary with display. The rate of self-fertilization increased for large floral displays, but siring losses due to geitonogamous pollen discounting were much greater than siring gains through increased self-fertilization. As display size increased, each additional seed sired through geitonogamous self-pollination was associated with a loss of 9·7 seeds sired through outcrossing.

Conclusions

Although total fitness increased with floral display size, the marginal return on each additional flower declined steadily as display size increased. Therefore, a plant could maximize fitness by producing small displays over a long flowering period, rather than large displays over a brief flowering period.     

Beyond the pollination syndrome: nectar ecology and the role of diurnal and nocturnal pollinators in the reproductive success of Inga sessilis (Fabaceae)

Inga species present brush‐type flower morphology allowing them to be visited by distinct groups of pollinators. Nectar features in relation to the main pollinators have seldom been studied in this genus. To test the hypothesis of floral adaptation to both diurnal and nocturnal pollinators, we studied the pollination ecology of Inga sessilis, with emphasis on the nectar secretion patterns, effects of sequential removals on nectar production, sugar composition and the role of diurnal and nocturnal pollinators in its reproductive success. Inga sessilis is self‐incompatible and pollinated by hummingbirds, hawkmoths and bats. Fruit set under natural conditions is very low despite the fact that most stigmas receive polyads with sufficient pollen to fertilise all ovules in a flower. Nectar secretion starts in the bud stage and flowers continually secreting nectar for a period of 8 h. Flowers actively reabsorbed the nectar a few hours before senescence. Sugar production increased after nectar removal, especially when flowers were drained during the night. Nectar sugar composition changed over flower life span, from sucrose‐dominant (just after flower opening, when hummingbirds were the main visitors) to hexose‐rich (throughout the night, when bats and hawkmoths were the main visitors). Diurnal pollinators contributed less than nocturnal ones to fruit production, but the former were more constant and reliable visitors through time. Our results indicate I. sessilis has floral adaptations, beyond the morphology, that encompass both diurnal and nocturnal pollinator requirements, suggesting a complementary and mixed pollination system.     

Crane flies and microlepidoptera also function as pollinators in Epidendrum (Orchidaceae: Laeliinae): the reproductive biology of E. avicula

Crane flies and microlepidoptera have been recorded as pollinators in unrelated orchid groups, but these insects have never been recorded in Epidendroideae, the most species‐rich orchid subfamily, which includes one of the most diverse genera among Orchidaceae, Epidendrum. Based on data on phenology, floral morpho‐anatomy, pollinators, pollination mechanisms and breeding system, the reproductive biology of E. avicula was studied in south‐eastern Brazil. Epidendrum avicula possess osmophores that produce a citric fragrance at night. The flowers attract Tipulidae flies and several families of microlepidoptera that drink the nectar produced in a tube formed by the adnation of the labellum and column. As is common in Epidendrum, after removing the pollinarium, both crane flies and micro‐moths get trapped by the proboscis, which frightens the insects and inhibits any possible intent to immediately visit another flower. The behavior of the pollinators on flowers, plus the retention of the anther cap by the pollinarium, results in a reduction in the occurrence of geitonogamy. Because E. avicula is self‐incompatible, the consequence of pollinator behavior and the floral mechanisms tend to reduce the pollen loss. As far as we know, this is the first study to report the reproductive biology of a species of Epidendroideae pollinated by crane flies and microlepidoptera. Based on more recent concepts of plant–pollinator interactions, although E. avicula is pollinated by several species belonging to two distinct orders, suggesting an unspecialized pollination system is involved, nectar‐seeking microlepidoptera and Tipulidae flies can be recognized as a single functional group.     

Sex pheromone mimicry in the early spider orchid (Ophrys sphegodes): patterns of hydrocarbons as the key mechanism for pollination by sexual deception

We investigated the female-produced sex pheromone of the solitary bee Andrena nigroaenea and compared it with floral scent of the sexually deceptive orchid Ophrys sphegodes which is pollinated by Andrena nigroaenea males. We identified physiologically and behaviorally active compounds by gas chromatography with electroantennographic detection, gas chromatography-mass spectrometry, and behavioral tests in the field. Dummies scented with cuticle extracts of virgin females or of O.sphegodes labellum extracts elicited significantly more male reactions than odorless dummies. Therefore, copulation behavior eliciting semiochemicals are located on the surface of the females' cuticle and the surface of the flowers. Within bee and orchid samples, n-alkanes and n-alkenes, aldehydes, esters, all-trans-farnesol and all-trans-farnesyl hexanoate triggered electroantennographic responses in male antennae. Most of the alkanes and alkenes occurred in similar patterns both in the bees and orchids. O. sphegodes leaf extracts contained mostly the same compounds but in different proportions. In behavioral tests with synthetic compounds, blends of alkenes triggered significantly more approaches and pounces of the males whereas alkanes were not more attractive than odorless dummies. Since alkanes and alkenes together were most attractive, we conclude they constitute the bees' sex pheromone as well as the pseudocopulation-behavior releasing orchid-odor bouquet. Accepted: 30 March 2000     

Pollination specialization and time of pollination on a tropical Venezuelan plain: variations in time and space

Levels of specialization of the pollination systems were evaluated in 155 plant species from the Venezuelan Central Plain. In all, 29 pollination systems were found, resulting from various combinations of nine pollen‐vector types or pollinating agent classes. The number of pollen‐vector types composing a pollination system ranged from one to five. Ninety‐one species were pollinated by only a single pollen‐vector type; the frequency of pollination systems fell monotonically with increasing number of constituent pollen‐vector types. Some 30–40 per cent of bee‐, moth‐, beetle‐ and bat‐pollinated species were pollinated by that group of vectors alone. The highest incidence of co‐occurrence between pollen‐vector types was found for the combinations fly–wasp, butterfly–wasp, butterfly–fly, and to a lesser extent bird–butterfly, bat–bird, bat–moth and butterfly–moth. The average number of pollen‐vector types per plant species was significantly higher for trees and shrubs than for lianas and perennial herbs. The distribution of polyphily, oligophily, monophily and anemophily was significantly associated with life form and habitat. The relative frequencies of these types varied least through the year in the forest‐savannah ecotone and in the vegetation as a whole, reflecting the combination of life forms. There were significantly fewer night‐pollinated than day‐pollinated species. Day‐pollinated species tended to be polyphilous, and most of the night‐pollinated species were monophilous or oligophilous. Time of pollination activity was related to habitat. The relative importance of night pollination among life forms decreased from trees to perennial herbs. Plant species exclusively pollinated during the night reached a peak during the rainy season (May to November) for trees, lianas and perennial herbs. The data as a whole show that the relative frequency of polyphily, oligophily, monophily and anemophily, and the time of pollination activity are influenced by community structure and plant species richness, and may change from season to season. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 145 , 1–16.     

Pollination by deceit in Paphiopedilum barbigerum (Orchidaceae): a staminode exploits the innate colour preferences of hoverflies (Syrphidae)

Paphiopedilum barbigerum T. Tang et F. T. Wang, a slipper orchid native to southwest China and northern Vietnam, produces deceptive flowers that are self‐compatible but incapable of mechanical self‐pollination (autogamy). The flowers are visited by females of Allograpta javana and Episyrphus balteatus (Syrphidae) that disperse the orchid’s massulate pollen onto the receptive stigmas. Measurements of insect bodies and floral architecture show that the physical dimensions of these two fly species correlate with the relative positions of the receptive stigma and dehiscent anthers of P. barbigerum. These hoverflies land on the slippery centralised wart located on the shiny yellow staminode and then fall backwards through the labellum entrance. They are temporarily trapped in the inflated chamber composed of the interconnected labellum and column. The attractive staminode of P. barbigerum strongly reflects the colour yellow (500–560 nm), a colour preferred innately by most pollen‐eating members of the Syrphidae. No scent molecules were detected using GC mass spectrometry analysis, showing that the primary attractant in this system is visual, not olfactory. Pollination‐by‐deceit in P. barbigerum is contrasted with its congener, P. dianthum, a brood site mimic that is pollinated by ovipositing females of E. balteatus. As the natural rate of fruit set in P. barbigerum (mean 26.3% pooled over three seasons) is lower than that of P. dianthum (mean 58.5% over two seasons), the evolution of false brood sites in some Paphiopedilum spp. should be selectively advantageous as they may provide an increase in the attention and return rates of dependable pollinators to flowers that always lack a reward.