First records of flower biology and pollination in African Annonaceae: Isolona, Piptostigma, Uvariodendron, Monodora and Uvariopsis

Seven species from five genera of Annonaceae were studied with regard to their flower biology and pollination in the Southwest Province of Cameroon, West Africa. They have protogynous hermaphroditic flowers, with exception of Uvariopsis species, which are monoecious. Fused petals of Isolona campanulata remain apically spreading and open during anthesis but form a deep basal urceolate tube around the reproductive organs. At anthesis the yellow pendent flowers emit a fruit-like scent and attracted small beetles, the likely pollinators. Piptostigma sp. flowers also emit a fruit-like scent but provide a closed pollination chamber formed by the three inner petals. Small staphylinid beetles attracted during the female stage of anthesis are released from the flowers at the end of the male stage 2-3 days later. Both species have diurnal anthesis, attracting and releasing the flower visitors during daytime. In contrast, Uvariodendron connivens and U. calophyllum have nocturnal anthesis with floral thermogenesis, produce spicy, aromatic and fruity scents and attract large Scarabaeidae beetles, the pollinators, along with many curculionid beetles, which were principally predators of the thick petals. The very large flowers of Monodora tenuifolia have yellowish petals which are spotted with dark red markings. Together with the sweetish, slightly disagreeable scent the flowers attract flies, principally dung flies. The two investigated Uvariopsis species are monoecious with pistillate and staminate flowers being functional at the same time. The violet red flowers of U. bakeriana visually seem to mimic the fruiting body of certain stinkhorn fungi (Phallaceae) although without producing their strong unpleasant carcass stench. Flower-visiting dung flies were rare. Conversely, U. congolana has a strong fungus-like scent, its flowers are presented at litter height and dung flies living in the litter were the flower visitors, albeit sporadic. The 4-5 days lasting anthesis of both Uvariopsis species appears to be an evolutionary consequence of their diffuse pollinator spectra. The studied African Annonaceae therefore have either cantharophilous or myiophilous/sapromyiophilous flowers with, in part, respectively, remarkably long anthesis, thermogenesis, and widely open, large flowers - all attributes unknown or rare in the hitherto better studied Neotropical Annonaceae.     

Specialized pollination in the African milkweed Xysmalobium orbiculare: a key role for floral scent in the attraction of spider-hunting wasps

Specialized pollination by prey-hunting wasps is poorly documented in rewarding plants. Furthermore, the mechanisms of achieving specialization are not clear since flowers typically produce exposed nectar and have no morphological adaptations (such as long spurs) to exclude non-pollinating visitors. We investigated the pollination of Xysmalobium orbiculare and explored the functional roles of floral scent and nectar in attracting pollinators and deterring nectar robbers. Floral visitor observations showed that this milkweed is visited almost exclusively by pompilid wasps in the genus Hemipepsis. These wasps were the only insects to carry pollinia, and a cage experiment confirmed their effectiveness in removing and inserting pollinia on flowers. Hand-pollinations showed that plants are genetically self-incompatible and thus reliant on pollinators for seed set. Palatability experiments with honeybees showed that nectar is distasteful to non-pollinating insects and is therefore likely to play a functional role in deterring nectar thieves. Choice experiments in the field showed that the wasp pollinators are attracted primarily by floral scent rather than visual cues. Analysis of spectral reflectance of flowers revealed that flowers are dull colored and are unlikely to stand out from the background vegetation. We conclude that X. orbiculare is specialized for pollination by spider-hunting wasps in the genus Hemipepsis and utilizes floral scent to selectively attract its pollinators and unpalatable nectar to deter non-pollinating visitors.     

Electrophysiological and behavioural responses of the housefly to “sweet” volatiles of the flowers of Caralluma europaea (Guss.) N.E. Br.

In sapromyiophilous plants, up to date, long range attraction of fly pollinators has been thoroughly investigated and attributed to “fetid” floral compounds, while the “sweet” floral scent fraction has not been specifically investigated and its role has received little attention. The aim of the present study was to verify if terpenoids, which are the main compounds of the floral bouquet of Caralluma europaea, play a role in the attraction of its pollinator Musca domestica. Terpinolene, α-terpinene and linalool, described as the three main volatiles of the flowers of C. europaea, were evaluated in electrophysiological investigations and blends of these compounds as well as the whole fresh flowers were used in behavioural assays. Antennae of housefly adults showed positive dose-dependent responses to all the chemicals tested. Houseflies were attracted by the odour of the fresh flowers and by the reconstructed terpenoid blend at the dose of 100 μg. At the dose of 10 μg, the blend did not produce any attraction. The results of the present study support the hypothesis that terpinolene, α-terpinene and linalool emitted by C. europaea flowers are involved in pollinator attraction and demonstrate the importance of the “sweet” scent in this sapromyiophilous species.     

Active pollination favours sexual dimorphism in floral scent

Zoophilous flowers often transmit olfactory signals to attract pollinators. In plants with unisexual flowers, such signals are usually similar between the sexes because attraction of the same animal to both male and female flowers is essential for conspecific pollen transfer. Here, we present a remarkable example of sexual dimorphism in floral signal observed in reproductively highly specialized clades of the tribe Phyllantheae (Phyllanthaceae). These plants are pollinated by species-specific, seed-parasitic Epicephala moths (Gracillariidae) that actively collect pollen from male flowers and pollinate the female flowers in which they oviposit; by doing so, they ensure seeds for their offspring. We found that Epicephala-pollinated Phyllanthaceae plants consistently exhibit major qualitative differences in scent between male and female flowers, often involving compounds derived from different biosynthetic pathways. In a choice test, mated female Epicephala moths preferred the scent of male flowers over that of female flowers, suggesting that male floral scent elicits pollen-collecting behaviour. Epicephala pollination evolved multiple times in Phyllantheae, at least thrice accompanied by transition from sexual monomorphism to dimorphism in floral scent. This is the first example in which sexually dimorphic floral scent has evolved to signal an alternative reward provided by each sex, provoking the pollinator''s legitimate altruistic behaviour.     

The missing stink: sulphur compounds can mediate a shift between fly and wasp pollination systems

The radiation of the angiosperms is often attributed to repeated evolutionary shifts between different pollinators, as this process drives diversification of floral forms and can lead to reproductive isolation. Floral scent is an important functional trait in many pollination systems but has seldom been implicated as a key mechanism in pollinator transitions. In this study, we suggest a role for sulphur compounds in mediating a shift between specialized carrion-fly and pompilid-wasp pollination systems in Eucomis (Hyacinthaceae). Flowers of closely related Eucomis species pollinated by carrion flies or pompilid wasps have very similar greenish-white flowers, but differ markedly in floral scent chemistry (determined by GC–MS analysis of headspace extracts). Comparison of the floral colours of the four Eucomis species in the visual systems of flies and wasps suggests that colour plays little role in pollinator discrimination. Nectar properties and morphology also do not differ strongly between fly- and wasp-pollinated flowers. By comparing floral scent bouquets and experimentally manipulating the scent of plants in the field, we demonstrate that shifts between wasp and fly pollination in these four congeners can depend on the production or suppression of sulphur compounds (dimethyl disulphide and dimethyl trisulphide) in the fragrance bouquet. This suggests that mutations affecting the production of particular scent compounds could precipitate shifts between pollinators, independently of floral morphology, colour or nectar properties.     

Floral volatiles play a key role in specialized ant pollination

Chemical signals emitted by plants are crucial to understand the ecology and evolution of plant–animal interactions. Scent is an important component of floral phenotype and represents a decisive communication channel between plants and floral visitors. Floral volatiles promote attraction of mutualistic pollinators and, in some cases, serve to prevent flower visitation by antagonists such as ants. Despite ant visits to flowers have been suggested to be detrimental to plant fitness, in recent years there has been a growing recognition of the positive role of ants in pollination. Nevertheless, the question of whether floral volatiles mediate mutualisms between ants and ant-pollinated plants still remains largely unexplored. Here we review the documented cases of ant pollination and investigate the chemical composition of the floral scent in the ant-pollinated plant Cytinus hypocistis. By using chemical-electrophysiological analyses and field behavioural assays, we examine the importance of olfactory cues for ants, identify compounds that stimulate antennal responses, and evaluate whether these compounds elicit behavioural responses. Our findings reveal that floral scent plays a crucial role in this mutualistic ant–flower interaction, and that only ant species that provide pollination services and not others occurring in the habitat are efficiently attracted by floral volatiles. 4-oxoisophorone, (E)-cinnamaldehyde, and (E)-cinnamyl alcohol were the most abundant compounds in Cytinus flowers, and ant antennae responded to all of them. Four ant pollinator species were significantly attracted to volatiles emitted by Cytinus inflorescences as well as to synthetic mixtures and single antennal-active compounds. The small amount of available data so far suggest that there is broad interspecific variation in floral scent composition among ant-pollinated plants, which could reflect differential responses and olfactory preferences among different ant species. Many exciting discoveries will be made as we enter into further research on chemical communication between ants and plants.     

Fly pollination in Ceropegia (Apocynaceae: Asclepiadoideae): biogeographic and phylogenetic perspectives

Background and Aims

Ceropegia (Apocynaceae subfamily Asclepiadoideae) is a large, Old World genus of >180 species, all of which possess distinctive flask-shaped flowers that temporarily trap pollinators. The taxonomic diversity of pollinators, biogeographic and phylogenetic patterns of pollinator exploitation, and the level of specificity of interactions were assessed in order to begin to understand the role of pollinators in promoting diversification within the genus.

Methods

Flower visitor and pollinator data for approx. 60 Ceropegia taxa were analysed with reference to the main centres of diversity of the genus and to a cpDNA–nrDNA molecular phylogeny of the genus.

Key Results

Ceropegia spp. interact with flower-visiting Diptera from at least 26 genera in 20 families, of which 11 genera and 11 families are pollinators. Size range of flies was 0·5–4·0 mm and approx. 94 % were females. Ceropegia from particular regions do not use specific fly genera or families, though Arabian Peninsula species are pollinated by a wider range of Diptera families than those in other regions. The basal-most clade interacts with the highest diversity of Diptera families and genera, largely due to one hyper-generalist taxon, C. aristolochioides subsp. deflersiana. Species in the more-derived clades interact with a smaller diversity of Diptera. Approximately 60 % of taxa are so far recorded as interacting with only a single genus of pollinators, the remaining 40 % being less conservative in their interactions. Ceropegia spp. can therefore be ecological specialists or generalists.

Conclusions

The genus Ceropegia has largely radiated without evolutionary shifts in pollinator functional specialization, maintaining its interactions with small Diptera. Intriguing biogeographic and phylogenetic patterns may reflect processes of regional dispersal, diversification and subsequent specialization onto a narrower range of pollinators, though some of the findings may be caused by inconsistent sampling. Comparisons are made with other plant genera in the Aristolochiaceae and Araceae that have evolved flask-shaped flowers that trap female flies seeking oviposition sites.Key words: Apocynaceae, Asclepiadoideae, Brachystelma, Ceropegia, Diptera, flower evolution, generalization, mutualism, pollination, Riocreuxia, specialization, Stapeliinae     

Nocturnal emission and post-pollination change of floral scent in the leafflower tree,Glochidion rubrum,exclusively pollinated by seed-parasitic leafflower moths

Many insect-pollinated plants use floral scent signals to attract and guide the effective pollinators, and temporal patterns of their floral scent emission may be tuned to respond to the pollinator's activity and pollination status. In the intimate nursery pollination mutualism between monoecious Glochidion trees (Phyllanthaceae) and Epicephala moths (Gracillariidae), floral scent signals mediate species-specific interactions and influence the moth's efficient pollen-collecting and pollen-depositing behaviors on male and female flowers, respectively. We tested the hypotheses that both sexes of flowers of Epicephala-pollinated Glochidion rubrum exhibit a diel pattern of scent emission matching the activity period of the nocturnally active pollinator, and that female flowers change the chemical signal after pollination to reduce further visits and oviposition by the pollinator. We investigated the diel change of floral scent emissions during two consecutive days and the influence of pollination on the floral scent by conducting hand-pollinations in the field. The total scent emission of male and female flowers was higher at night than in the day, which would be expected from the nocturnal visitations of Epicephala moths. Some compounds exhibited a clear nocturnal emission rhythm. Hand-pollination experiments revealed that emission of two compounds, nerolidol and eugenol, drastically decreased in pollinated flowers, suggesting that these compounds may function as key attractants for the pollinator; however, the total scent emission of the female flower was not influenced by hand-pollination. The pattern of the floral scent emission of G. rubrum may be optimized to attract nocturnal pollinators and reduce oviposition.     

Generalized fly-pollination in Ceropegia ampliata (Apocynaceae�CAsclepiadoideae): the role of trapping hairs in pollen export and receipt

Flowers of most species in the genus Ceropegia have elaborate adaptations to trap pollinating flies. Flies are trapped within a bulbous base of the flower after moving through an elongated corolla tube that is frequently lined with stiff hairs. When these hairs wilt after several days, insects held in the bulbous chamber at the base of the corolla tube are released. Despite such complex adaptations for trapping pollinators, key aspects of the pollination ecology including the identity of pollinators, presence or absence of nectar rewards, duration of pollinator trapping, and pollination success remain undescribed for most Ceropegia species. Importantly, no studies have empirically tested the role that trapping hairs may have on pollen export and receipt. We documented the pollination biology of Ceropegia ampliata in two natural populations and found that C. ampliata can be regarded as a generalist, being pollinated by flies from at least four families (Tachinidae, Sarcophagidae, Muscidae, and Lauxaniidae). The duration of the trapping phase lasted 2?C5?days and flowers produce small quantities of nectar. Pollination success was highly variable but generally low with occasional peaks suggesting that flies are likely to visit this species sporadically. Flowers that had already proceeded beyond the trapping phase generally had a significantly greater number of pollinaria removed than flowers that were still in the trapping phase, probably reflecting the longer exposure to pollinators. In contrast we found no differences in pollinarium removal between flowers with trapping hairs present and flowers with hairs experimentally disabled. The role of trapping hairs in the pollination success of C. ampliata therefore remains uncertain although we propose, on the basis of this experiment, that trapping may be an adaptation to enhance female success through pollen deposition rather than pollen export. Given the low rates of natural pollen deposition, an experiment with a large number of replicates is required to test this hypothesis in Ceropegia.     

Intraspecific Variation of Floral Scent Chemistry in Magnolia kobus DC. (Magnoliaceae)

Magnolia kobus was examined at 32 sites in Japan (109 female-stage flowers from 52 plants) by GC-MS. Major chemical compounds (a total of 36 chemicals) emitted from the flowers were: linalool (and its oxides), limonene, cis- and trans-β-Ocimene, benzaldehyde, benzyl alcohol, benzyl cyanide, and 2-aminobenzaldehyde. Linalool and its oxides were the most abundant components of floral scents in 21 individuals. The rate at which chemical volatiles were emitted ranged from 0.002 to 0.929 μg/flower/hour (average 0.211). High quantitative and qualitative variation in floral scent chemistry among individuals was found throughout the range of M. kobus, especially in central Honshu. The high variability in floral scent chemistry may be due to the importance of visual cues in the reproductive biology of M. kobus which flowers in early spring, resulting in decreased selection for specific floral scent profiles. Alternatively, different scent compounds or chemical profiles may be equally effective in attracting pollinators. Received 25 June 2001/ Accepted in revised form 25 August 2001     

Genetic aspects of floral fragrance in plants

It is generally assumed that compounds are emitted from flowers in order to attract and guide pollinators. Due to the invisibility and the highly variable nature of floral scent, no efficient and reliable methods to screen for genetic variation have been developed. Moreover, no convenient plant model systems are available for flower scent studies. In the past decade, several floral fragrance-related genes have been cloned; the biosynthesis and metabolic engineering of floral volatiles have been studied with the development of biotechnology. This review summarizes the reported floral fragrance-related genes and the biosynthesis of floral scent compounds, introduces the origin of new modification enzymes for flower scent, compares different methods for floral fragrance-related gene cloning, and discusses the metabolic engineering of floral scent. Finally, the perspectives and prospects of research on floral fragrance are presented. Published in Russian in Biokhimiya, 2007, Vol. 72, No. 4, pp. 437–446.     

Adaptive radiation of the putrid perianth: Ferraria (Iridaceae: Irideae) and its unusual pollinators

Field studies of 13 of the estimated 17 species of the southern African geophytic genus Ferraria (Iridaceae: Iridoideae) identified four distinct pollination systems. Ferraria flowers are radially symmetric and cupped with a large, mostly pale or dull-colored perianth. Perigonal nectaries secrete hexose dominant (fructose and glucose) nectar. Most species are pollinated by Diptera of four families, apparently attracted by strong floral odors, mostly putrid or fermenting, but sometimes apparently sweet, and a large perianth mottled and edged with dark color. Concentrated sugary secretions are produced on the tepal claws that form a shallow floral cup. In contrast, flowers of F. ferrariola have a deep, narrow floral cup, a pale blue or yellow perianth, and a spicy scent and are pollinated by bees in the family Apidae, rewarded by nectar of moderate sugar concentration. Ferraria divaricata and F. variabilis have dull-colored, darkly speckled or streaked perianths and produce ample, highly dilute nectar pooled at the base of the floral cup and are pollinated by eumenid and masarine wasps (Vespidae). Lastly, F. uncinata has flowers with a narrow floral cup and dull violet tepals with brown margins. They are visited only by meloid and melyrid beetles. All pollen transfers from the anther of a Ferraria flower to an insect’s body are passive, regardless of pollinator. Pollen load analyses suggests that all pollinators show a high degree of faithfulness to Ferraria flowers.     

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.     

Floral attraction and flower visitors of a subcanopy,tropical rainforest tree,Fontainea picrosperma

1. Flowering plants in tropical rainforests rely heavily on pollen vectors for successful reproduction. Research into pollination systems in tropical rainforests is dominated by canopy species, while subcanopy plant–pollinator interactions remain under‐represented. The microclimate beneath the rainforest canopy is characterized by low light levels and is markedly different from the canopy environment that receives more light energy.
2. We studied the floral attractants and floral visitors of a dioecious, subcanopy tree, Fontainea picrosperma (Euphorbiaceae), in the Wet Tropics bioregion of northern Queensland, Australia.
3. We found that wind pollination is rare and male and female flowers do not produce nectar. Female flowers are likely pollinated due to their perceptual similarity to pollen‐offering male flowers. Female flowers had the same scent profile as male flowers, and floral scent was an important floral attractant that acted to regulate pollinator behavior. The two most abundant scent compounds present in the floral bouquet were benzyl alcohol and 4‐oxoisophorone. These compounds are ubiquitous in nature and are known to attract a wide variety of insects. Both day‐time and night‐time pollinators contributed to successful pollen deposition on the stigma, and diurnal flower visitors were identified from several orders of insects including beetles, flies, predatory wasps, and thrips. Fontainea picrosperma is therefore likely to be pollinated by a diverse array of small insects.
4. Synthesis. Our data indicate that F. picrosperma has a generalist, entomophilous pollination syndrome. The rainforest subcanopy is a distinctive environment characterized by low light levels, low or turbulent wind speeds, and relatively high humidity. Female flowers of F. picrosperma exhibit cost‐saving strategies by not producing nectar and mimicking the smell of reward‐offering male flowers. Insects opportunistically forage on or inhabit flowers, and pollination occurs from a pool of small insects with low energy requirements that are found beneath the rainforest canopy.

     

Can fine-scale post-pollination variation of fig volatile compounds explain some steps of the temporal succession of fig wasps associated with Ficus racemosa?

Volatile organic compounds (VOCs) emitted by flowers play an essential role in mediating the attraction of pollinators. However, they also attract other species exploiting resources associated with flowers. For instance, VOCs emitted by figs play a major role in encounters between Ficus spp., their mutualistic pollinating wasps, and all the members of the community of non-pollinating fig wasps (NPFWs) that exploit the mutualistic interaction. Because pollinators might be in limited supply for a tree bearing many inflorescences, the plant might maximize its individual reproductive success by reducing the attractiveness of inflorescences once they are pollinated, so that pollinators orient only towards the tree's unpollinated figs. Changes in VOCs emission that bring this about could represent an important cue for NPFWs that exploit particular stages of fig development. In this study, by monitoring precisely the presence of fig-associated wasps on figs of F. racemosa, a common widespread fig species, we demonstrated that 4–5 days and 15 days following pollination represent two critical transitional steps in the succession of different wasp species. Then, focusing on the first one of these transitional steps, by investigating the composition of fig VOCs at receptivity and from 1 to 5 days following pollination, we detected progressive quantitative and qualitative variation of floral scent following pollination. These changes are significant at 5 days following pollination. The qualitative changes are mainly due to an increase in the relative proportions of two monoterpenes (α-pinene and limonene). These variations of the floral VOCs following pollination could explain why pollinating wasps stop visiting figs very shortly after the first pollinators enter receptive figs. They also possibly explain the succession of non-pollinating wasps on the figs following pollination.     

Floral scents of chafer-pollinated asclepiads and a potential hybrid

Floral scent is a key functional trait for pollinator attraction to flowers, but is poorly documented in many plant lineages and pollination systems. In South African grasslands, chafer beetles (Scarabaeidae: Cetoniinae), particularly Atrichelaphinis tigrina, Cyrtothyrea marginalis and Leucoscelis spp., are common floral visitors and specialized pollination by these beetles has recently been established in several asclepiad, orchid and protea species. Chafer beetles are known to be attracted by a variety of floral volatile compounds and scent has been suggested to be an important signal in these chafer-operated pollination systems. In this study, we used dynamic headspace extraction methods and coupled gas chromatography–mass spectrometry (GC–MS) to examine the chemical composition of the floral scents of seven putatively chafer-pollinated asclepiad species in the genera Asclepias, Pachycarpus and Xysmalobium. We identified 15–57 compounds in the scents of these species, of which seven were common to all species examined. The scent profiles of each species separate into discrete clusters in two dimensional space based on non-metric multidimensional scaling (NMDS), indicating clear distinctions between species and suggesting that plants may use different combinations of volatiles to attract beetles. Two plants suspected to be intergeneric hybrids were also examined. Data on pollination systems, morphology and scent chemistry are consistent with the hypothesis that these plants are hybrids between the chafer-pollinated species Asclepias woodii and Pachycarpus concolor. The results of this study are discussed in relation to the role of chafer beetles as generalist pollinators of specialized asclepiads.     

Pollination of the “carrion flowers” of an African stapeliad (<Emphasis Type="Italic">Ceropegia mixta</Emphasis>: Apocynaceae): the importance of visual and scent traits for the attraction of flies

Flowers that mimic carrion or faeces exhibit unusual traits, the evolution and functional significance of which remain poorly understood. Odour is an important pollinator attractant, but visual traits and interactions between visual and scent traits have seldom been considered. We studied pollination of the “carrion flowers” of Ceropegia mixta [= Orbea variegata], analysed floral traits and used manipulative experiments to explore the contributions of visual and scent traits to pollinator attraction. Flowers were pollinated primarily by Musca domestica (Muscidae), with lesser contributions by Calliphoridae and Sarcophagidae flies. The floral odour (analysed using gas chromatography–mass spectrometry) was dominated by oligosulphides and phenol. Comparison of floral and abiotic background colours (analysed using reflectance spectrometry) using a fly colour vision model suggested that flowers would be chromatically indistinguishable from the background. Comparison of fly arrival rates at concealed (but still scented) versus exposed flowers showed that flies can locate flowers without visual cues, but visitation was higher when the flowers were visible. Experiments using model flowers with odour supplied by real flowers (to explore the significance of dark flowers and dark spots on a pale background, which both occur frequently in flowers that mimic carrion or faeces) showed that scented black flowers attracted significantly more flies than similarly scented human-yellow flowers, while the presence or size of black spots on the corolla had no effect on the attraction of flies. Our results suggest that there is a visual component to fly attraction, but some traits, such as the mottled patterning, may not have evolved to enhance pollinator attraction.     

Interpopulation variation in pollinators and floral scent of the lady’s-slipper orchid <Emphasis Type="Italic">Cypripedium calceolus</Emphasis> L.

Floral scent is a key mediator in many plant–pollinator interactions. It is known to vary not only among plant species, but also within species among populations. However, there is a big gap in our knowledge of whether such variability is the result of divergent selective pressures exerted by a variable pollinator climate or alternative scenarios (e.g., genetic drift). Cypripedium calceolus is a Eurasian deceptive lady’s-slipper orchid pollinated by bees. It is found from near sea level to altitudes of 2500 m. We asked whether pollinator climate and floral scents vary in a concerted manner among different altitudes. Floral scents of four populations in the Limestone Alps were collected by dynamic headspace and analyzed by gas chromatography coupled to mass spectrometry (GC/MS). Flower visitors and pollinators (the subset of visitors with pollen loads) were collected and identified. Preliminary coupled gas chromatographic and electroantennographic measurements with floral scents and pollinators revealed biologically active components. More than 70 compounds were detected in the scent samples, mainly aliphatics, terpenoids, and aromatics. Although several compounds were found in all samples, and all samples were dominated by linalool and octyl acetate, scents differed among populations. Similarly, there were strong differences in flower visitor spectra among populations with most abundant flower visitors being bees and syrphid flies at low and high altitudes, respectively. Pollinator climate differed also among populations; however, independent of altitude, most pollinators were bees of Lasioglossum, Andrena, and Nomada. Only few syrphids acted as pollinators and this is the first record of flies as pollinators in C. calceolus. The electrophysiological tests showed that bees and syrphid flies sensed many of the compounds released by the flowers, among them linalool and octyl acetate. Overall, we found that both floral scent and visitor/pollinator climate differ among populations. We discuss whether interpopulation variation in scent is a result of pollinator-mediated selection.     

Heterodichogamy and nitidulid beetle pollination in Anaxagorea prinoides, an early divergent Annonaceae

Heterodichogamy in a natural population of an Annonaceae species from the rainforests of French Guiana is described for the first time. Anaxagorea prinoides had bisexual flowers and two floral morphs within the studied population were protogynous. The population under study comprised 7 mature trees belonging to one morph and 12 to the other. Statistical analyses showed that the two morphs were in a 50:50% ratio, and therefore the temporal sexual pattern of heterodichogamy is given. When anthesis of flowers in the male stage ended in one morph, anthesis started with flowers in the female stage in the complementary morph. Approximately 1?h before the end of anthesis in one morph, flowers of the reciprocal morph started to emit a fruit-like scent. The temporal separation of the female and the male stages of the two different morphs lasted only approximately 1?h. Six of the seven identified compounds in the banana-like floral scent were esters and one was an alcohol. The main compounds examined are known to be components of fruit scents. Nitidulidae beetles of the genus Colopterus were the pollinators of A. prinoides and during flowering were maintained within the population of this species. This was not only due to the fact that the beetles remained sheltered in the pollination chamber of the flowers, but also because upon release from individuals of male-stage flowers at the end of flower anthesis they were attracted by the odoriferous female-stage flowers of other individuals of the same population. Heterodichogamy of A. prinoides appears to be a means by which reproductive success is augmented. Attraction of beetle pollinators by ??fruit-imitating?? floral scent is not restricted to species of Anaxagorea, but occurs in many representatives of the Annonaceae.