Headspace analysis of volatile flower scent constituents of bat-pollinated plants

To be or not to be fragrant: floral scent of some bat-pollinated cacti

Floral scent is a key olfactory cue in both diurnal and nocturnal pollination systems. In the case of nocturnal systems, such as bat-pollinated flowers, odour seems to play a more important role than visual cues. Cactaceae include many bat-pollinated species; however, few studies have investigated the olfactory cues in this family. We analysed and compared the chemical composition of the floral bouquet of three chiropterophilous cactus species, among which are a pair of congeners that differ considerably in scent intensity. Our research presents novel findings regarding the floral scent chemistry of chiropterophilous cactus species. We documented the first case of a bat-pollinated cactus whose flowers lack perceptible floral scent and in which no volatile compounds were detected in our chemical analyses. Additionally, we provide a comprehensive analysis of the chemical composition of the floral bouquet of the other two bat-pollinated species, revealing a resemblance among closely related species within the same genus. We highlight the need for further studies using biotests to investigate the mechanisms through which bats find flowers lacking scent.

Rodent responses to volatile compounds provide insights into the function of floral scent in mammal-pollinated plants

Flowers pollinated by mammals have evolved in many plant families. Several scent compounds that attract bats to flowers have been identified, but the chemical ecology of pollination mutualisms between plants and ground-dwelling mammals is poorly understood. Rodents are key pollinators in South Africa and rely heavily on olfaction to locate food. Our aim was to identify compounds that may function to attract rodents to flowers. Eighteen volatile compounds, including 14 that are prominent in the scent of rodent-pollinated flowers, were used in choice experiments involving wild-caught individuals of four native rodent species. Rodents were generally attracted to oxygenated aliphatic compounds, specifically ketones and esters, but not to some aromatic compounds common in floral scents of insect-pollinated species, nor to a sulfide compound that is attractive to bats. Associative conditioning using sugar solution as a reward had only weak effects on the attractiveness of compounds to rodents. The attractive effect of some compounds disappeared when they were blended with compounds that did not attract rodents. We conclude that aliphatic ketones and esters are likely to play a key role in attracting rodents to flowers. Deployment of these compounds may allow plants to exploit rodent sensory bias that evolved in other contexts such as intra-specific communication and searching for seeds. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Odor-Pollution From Fungicides Disrupts Learning and Recognition of a Common Floral Scent in Bumblebees (Bombus impatiens)

Background and Aims

Bumblebees provide vital pollination services to both natural and agricultural ecosystems. Consequently their declines in species-diversity and population size over the last five decades is alarming. Direct contributors to these declines include pesticides, habitat loss, and disease. However, given that colony fitness is linked to foraging success, successful conservation requires mitigation of any anthropogenic practices that negatively impact foraging. Previous work has shown that agrochemical odor-pollution, including that of fungicides, can modulate bumblebee foraging behavior. This study investigates how odor pollution from three common fungicides (Safer® Brand Garden Fungicide II, Scotts® Lawn Fungus Control, and Reliant® Systemic Fungicide) affects Bombus impatiens’ floral-odor learning and recognition using an associative learning paradigm.

Methods

The effects of fungicide-odor pollution were tested in three ways: (1) background pollution during floral-odor learning; (2) background pollution during floral-odor recognition; and (3) point (localized) pollution during floral-odor recognition. Electroantennogram (EAG) recordings from B. impatiens confirmed the salience of all odor-stimuli and examined impacts of background fungicide-odor on antennal responses to floral-odor. To better understand how fungicide-odor structure related to behavioral data, scents were sampled (Solid Phase Microextraction) and analyzed using gas chromatography–mass spectrometry. Odors were then characterized using the Compounds Without Borders (CWB) vectorization method.

Conclusion

All fungicides tested disrupted floral-odor learning and recognition for at least one concentration tested, and Scotts® was universally disruptive at all tested concentrations. All fungicides induced EAG responses, indicating they provide perceivable odor stimuli. Interestingly, two of three tested fungicides (Scotts® and Reliant®) inhibit antennal responses to Monarda fistulosa odor. Odor characterization supports previous findings that sulfurous scents could be disruptive to odor-driven foraging behaviors. Inability for foraging bumblebees to associate to rewarding floral odors in the presence of fungicidal odor pollution could have negative large-scale implications for colony health and reproductive fitness.

Deciphering the Biotic and Climatic Factors That Influence Floral Scents: A Systematic Review of Floral Volatile Emissions

Currently, a global analysis of the information available on the relative composition of the floral scents of a very diverse variety of plant species is missing. Such analysis may reveal general patterns on the distribution and dominance of the volatile compounds that form these mixtures, and may also allow measuring the effects of factors such as the phylogeny, pollination vectors, and climatic conditions on the floral scents of the species. To fill this gap, we compiled published data on the relative compositions and emission rates of volatile organic compounds (VOCs) in the floral scents of 305 plant species from 66 families. We also gathered information on the groups of pollinators that visited the flowers and the climatic conditions in the areas of distribution of these species. This information allowed us to characterize the occurrence and relative abundances of individual volatiles in floral scents and the effects of biotic and climatic factors on floral scent. The monoterpenes trans-β-ocimene and linalool and the benzenoid benzaldehyde were the most abundant floral VOCs, in both ubiquity and predominance in the floral blends. Floral VOC richness and relative composition were moderately preserved traits across the phylogeny. The reliance on different pollinator groups and the climate also had important effects on floral VOC richness, composition, and emission rates of the species. Our results support the hypothesis that key compounds or compounds originating from specific biosynthetic pathways mediate the attraction of the main pollinators. Our results also indicate a prevalence of monoterpenes in the floral blends of plants that grow in drier conditions, which could link with the fact that monoterpene emissions protect plants against oxidative stresses throughout drought periods and their emissions are enhanced under moderate drought stress. Sesquiterpenes, in turn, were positively correlated with mean annual temperature, supporting that sesquiterpene emissions are dominated mainly by ambient temperature. This study is the first to quantitatively summarise data on floral-scent emissions and provides new insights into the biotic and climatic factors that influence floral scents.

Identification of Odor-Active Compounds Released from a Damaged Plant of the Asian Skunk Cabbage Symplocarpus renifolius

Symplocarpus renifolius (Asian skunk cabbage) is a perennial herb of the Araceae family. As its common name implies, this plant produces a strong garliclike irritant odor with a rotten note when the plant parts are crushed. To elucidate the odor characteristics, the volatile compounds released from crushed plant parts (rhizome, petioles, and leaf blades) of S. renifolius were identified by a dynamic headspace method. Fifteen sulfur compounds were identified as odor-active compounds by gas chromatography-mass spectrometry-olfactometry (GC-MS-O). The sulfur compounds may be responsible for the strong odor emitted by crushed skunk cabbage. Many of the compounds lack a carbon-carbon bond, and all of the carbon atoms are connected to sulfur. This is regarded as the characteristic structure of the sulfur compounds released from the damaged plant parts of the skunk cabbage. Nine of the sulfur compounds were detected in all three of the plant parts analyzed in this study: hydrogen sulfide, methanethiol, 1-hexanethiol, methyl dithioformate, 2,4-dithiapentane, dimethyl trisulfide, methional, 2,3,5-trithiahexane, and tris(methylthio)methane. Methyl dithioformate and methylthiomethyl dithioformate were identified for the first time as natural products.

First Characterisation of Volatile Organic Compounds Emitted by Banana Plants

Banana (Musa sp.) ranks fourth in term of worldwide fruit production, and has economical and nutritional key values. The Cavendish cultivars correspond to more than 90% of the production of dessert banana while cooking cultivars are widely consumed locally around the banana belt production area. Many plants, if not all, produce Volatile Organic Compounds (VOCs) as a means of communication with their environment. Although flower and fruit VOCs have been studied for banana, the VOCs produced by the plant have never been identified despite their importance in plant health and development. A volatile collection methodology was optimized to improve the sensitivity and reproducibility of VOCs analysis from banana plants. We have identified 11 VOCs for the Cavendish, mainly (E,E)-α-farnesene (87.90 ± 11.28 ng/μl), methyl salicylate (33.82 ± 14.29) and 6-methyl-5-hepten-2-one (29.60 ± 11.66), and 14 VOCs for the Pacific Plantain cultivar, mainly (Z,E)-α-farnesene (799.64 ± 503.15), (E,E)-α-farnesene (571.24 ± 381.70) and (E) β ocimene (241.76 ± 158.49). This exploratory study paves the way for an in-depth characterisation of VOCs emitted by Musa plants.

The role of metals in mammalian olfaction of low molecular weight organosulfur compounds

Covering: up to the end of 2017While suggestions concerning the possible role of metals in olfaction and taste date back 50 years, only recently has it been possible to confirm these proposals with experiments involving individual olfactory receptors (ORs). A detailed discussion of recent experimental results demonstrating the key role of metals in enhancing the response of human and other vertebrate ORs to specific odorants is presented against the backdrop of our knowledge of how the sense of smell functions both at the molecular and whole animal levels. This review emphasizes the role of metals in the detection of low molecular weight thiols, sulfides, and other organosulfur compounds, including those found in strong-smelling animal excretions and plant volatiles, and those used in gas odorization. Alternative theories of olfaction are described, with evidence favoring the modified "shape" theory. The use of quantum mechanical/molecular modeling (QM/MM), site-directed mutagenesis and saturation-transfer-difference (STD) NMR is discussed, providing support for biological studies of mouse and human receptors, MOR244-3 and OR OR2T11, respectively. Copper is bound at the active site of MOR244-3 by cysteine and histidine, while cysteine, histidine and methionine are involved with OR2T11. The binding pockets of these two receptors are found in different locations in the three-dimensional seven transmembrane models. Another recently deorphaned human olfactory receptor, OR2M3, highly selective for a thiol from onions, and a broadly-tuned thiol receptor, OR1A1, are also discussed. Other topics covered include the effects of nanoparticles and heavy metal toxicants on vertebrate and fish ORs, intranasal zinc products and the loss of smell (anosmia).

Finding flowers in the dark: nectar-feeding bats integrate olfaction and echolocation while foraging for nectar

Nectar-feeding bats depend mainly on floral nectar to fulfil their energetic requirements. Chiropterophilous flowers generally present strong floral scents and provide conspicuous acoustic echoes to attract bats. While floral scents are assumed to attract bats over long distances, acoustic properties of flower structures may provide detailed information, thus supporting the localization of a flower at close ranges. So far, to our knowledge, there is no study trying to understand the relative importance as well as the combination of these generally coupled cues for detection (presence) and localization (exact position) of open flowers in nature. For a better comprehension of the significance of olfaction and echolocation in the foraging behaviour of nectar-feeding bats, we conducted two-choice experiments with Leptonycteris yerbabuenae. We tested the bats' behaviour in three experimental scenarios with different cues: (i) olfaction versus echolocation, (ii) echolocation versus echolocation and olfaction, and (iii) olfaction versus echolocation and olfaction. We used the floral scent of the bat-pollinated cactus Pachycereus pringlei as olfactory cue and an acrylic paraboloid as acoustic cue. Additionally, we recorded the echolocation behaviour of the bats and analysed the floral scent of P. pringlei. When decoupled cues were offered, bats displayed no preference in choice for any of the two cues. However, bats reacted first to and chose more often the coupled cues. All bats echolocated continuously and broadcast a long terminal group before a successful visit. The floral scent bouquet of P. pringlei is composed of 20 compounds, some of which (e.g. methyl benzoate) were already reported from chiropterophilous plants. Our investigation demonstrates for the first time to our knowledge, that nectar-feeding bats integrate over different sensory modes for detection and precise localization of open flowers. The combined information from olfactory and acoustic cues allows bats to forage more efficiently.

Flower power and the mustard bomb: Comparative analysis of gene and genome duplications in glucosinolate biosynthetic pathway evolution in Cleomaceae and Brassicaceae

PREMISE OF THE STUDY

Glucosinolates (GS) are a class of plant secondary metabolites that provide defense against herbivores and may play an important role in pollinator attraction. Through coevolution with plant-interacting organisms, glucosinolates have diversified into a variety of chemotypes through gene sub- and neofunctionalization. Polyploidy has been of major importance in the evolutionary history of these gene families and the development of chemically separate GS types. Here we study the effects of polyploidy in Tarenaya hassleriana (Cleomaceae) on the genes underlying GS biosynthesis.

METHODS

We established putative orthologs of all gene families involved in GS biosynthesis through sequence comparison and their duplication method through calculation of synonymous substitution ratios, phylogenetic gene trees, and synteny comparison. We drew expression data from previously published work of the identified genes and compared expression in several tissues.

KEY RESULTS

We show that the majority of gene family expansion in T. hassleriana has taken place through the retention of polyploid duplicates, together with tandem and transpositional duplicates. We also show that the large majority (>75%) is actively expressed either globally or in specific tissues. We show that MAM and CYP83 gene families, which are crucial to GS diversification in Brassicaceae, are also recruited into specific tissue expression pathways in Cleomaceae.

CONCLUSIONS

Many GS genes have expanded through polyploidy, gene transposition duplication, and tandem duplication in Cleomaceae. Duplicate retention through these mechanisms is similar to A. thaliana, but based on the expression of GS genes, Cleomaceae-specific diversification of GS genes has taken place.

The Complexity of Background Clutter Affects Nectar Bat Use of Flower Odor and Shape Cues

Given their small size and high metabolism, nectar bats need to be able to quickly locate flowers during foraging bouts. Chiropterophilous plants depend on these bats for their reproduction, thus they also benefit if their flowers can be easily located, and we would expect that floral traits such as odor and shape have evolved to maximize detection by bats. However, relatively little is known about the importance of different floral cues during foraging bouts. In the present study, we undertook a set of flight cage experiments with two species of nectar bats (Anoura caudifer and A. geoffroyi) and artificial flowers to compare the importance of shape and scent cues in locating flowers. In a training phase, a bat was presented an artificial flower with a given shape and scent, whose position was constantly shifted to prevent reliance on spatial memory. In the experimental phase, two flowers were presented, one with the training-flower scent and one with the training-flower shape. For each experimental repetition, we recorded which flower was located first, and then shifted flower positions. Additionally, experiments were repeated in a simple environment, without background clutter, or a complex environment, with a background of leaves and branches. Results demonstrate that bats visit either flower indiscriminately with simple backgrounds, with no significant difference in terms of whether they visit the training-flower odor or training-flower shape first. However, in a complex background olfaction was the most important cue; scented flowers were consistently located first. This suggests that for well-exposed flowers, without obstruction from clutter, vision and/or echolocation are sufficient in locating them. In more complex backgrounds, nectar bats depend more heavily on olfaction during foraging bouts.

MC, Krömer T, García-Franco JG, Knauer A, Kessler M. First record of bat-pollination in the species-rich genus Tillandsia (Bromeliaceae)

BACKGROUND AND AIMS

Bromeliaceae is a species-rich neotropical plant family that uses a variety of pollinators, principally vertebrates. Tillandsia is the most diverse genus, and includes more than one-third of all bromeliad species. Within this genus, the majority of species rely on diurnal pollination by hummingbirds; however, the flowers of some Tillandsia species show some characteristics typical for pollination by nocturnal animals, particularly bats and moths. In this study an examination is made of the floral and reproductive biology of the epiphytic bromeliad Tillandsia macropetala in a fragment of humid montane forest in central Veracruz, Mexico.

METHODS

The reproductive system of the species, duration of anthesis, production of nectar and floral scent, as well as diurnal and nocturnal floral visitors and their effectiveness in pollination were determined.

KEY RESULTS

Tillandsia macropetala is a self-compatible species that achieves a higher fruit production through outcrossing. Nectar production is restricted to the night, and only nocturnal visits result in the development of fruits. The most frequent visitor (75 % of visits) and the only pollinator of this bromeliad (in 96 % of visits) was the nectarivorous bat Anoura geoffroyi (Phyllostomidae: Glossophaginae).

CONCLUSIONS

This is the first report of chiropterophily within the genus Tillandsia. The results on the pollination biology of this bromeliad suggest an ongoing evolutionary switch from pollination by birds or moths to bats.

Scent glands in legume flowers

Scent glands, or osmophores, are predominantly floral secretory structures that secrete volatile substances during anthesis, and therefore act in interactions with pollinators. The Leguminosae family, despite being the third largest angiosperm family, with a wide geographical distribution and diversity of habits, morphology and pollinators, has been ignored with respect to these glands. Thus, we localised and characterised the sites of fragrance production and release in flowers of legumes, in which scent plays an important role in pollination, and also tested whether there are relationships between the structure of the scent gland and the pollinator habit: diurnal or nocturnal. Flowers in pre-anthesis and anthesis of 12 legume species were collected and analysed using immersion in neutral red, olfactory tests and anatomical studies (light and scanning electron microscopy). The main production site of floral scent is the perianth, especially the petals. The scent glands are distributed in a restricted way in Caesalpinia pulcherrima, Anadenanthera peregrina, Inga edulis and Parkia pendula, constituting mesophilic osmophores, and in a diffuse way in Bauhinia rufa, Hymenaea courbaril, Erythrostemon gilliesii, Poincianella pluviosa, Pterodon pubescens, Platycyamus regnellii, Mucuna urens and Tipuana tipu. The glands are comprised of cells of the epidermis and mesophyll that secrete mainly terpenes, nitrogen compounds and phenols. Relationships between the presence of osmophores and type of anthesis (diurnal and nocturnal) and the pollinator were not found. Our data on scent glands in Leguminosae are original and detail the type of diffuse release, which has been very poorly studied.

Chemical mimicry of insect oviposition sites: a global analysis of convergence in angiosperms

Floral mimicry of decaying plant or animal material has evolved in many plant lineages and exploits, for the purpose of pollination, insects seeking oviposition sites. Existing studies suggest that volatile signals play a particularly important role in these mimicry systems. Here, we present the first large-scale phylogenetically informed study of patterns of evolution in the volatile emissions of plants that mimic insect oviposition sites. Multivariate analyses showed strong convergent evolution, represented by distinct clusters in chemical phenotype space of plants that mimic animal carrion, decaying plant material, herbivore dung and omnivore/carnivore faeces respectively. These plants deploy universal infochemicals that serve as indicators for the main nutrients utilised by saprophagous, coprophagous and necrophagous insects. The emission of oligosulphide-dominated volatile blends very similar to those emitted by carrion has evolved independently in at least five plant families (Annonaceae, Apocynaceae, Araceae, Orchidaceae and Rafflesiaceae) and characterises plants associated mainly with pollination by necrophagous flies and beetles.

Strong phylogenetic effects on floral scent variation of oil-secreting orchids in South Africa

PREMISE OF THE STUDY

Evolution involves the interplay between natural selection and phylogenetic constraint. This is particularly evident among the flowering plants where form and diversity of flowers attest to the importance of both pollinator-mediated selection and phylogenetic constraint. Although this has been studied mostly using visible floral characters, invisible volatile chemicals emitted by the flowers should be subject to these same evolutionary forces. Unfortunately, most analyses of floral volatiles have over-emphasized the importance of natural selection and underplayed phylogenetic constraint without quantifying their respective roles in the evolution and composition of floral scents.

METHODS

We used multivariate analyses to test the relative importance of pollinators vs. phylogeny in determining the composition of floral scents among oil-secreting orchids in southern Africa. Floral scents of 42 oil-secreting taxa/ecotypes distributed among 12 subclades in the tribe Diseae were sampled using headspace adsorption and gas chromatography-mass spectroscopy.

KEY RESULTS

We identified 257 scent compounds distributed over nine different compound classes, with the majority of scents dominated by aliphatic or benzenoid compounds. The only significant predictor of floral scent among these orchids above the species level was phylogeny. Nevertheless, in two of the clades there were differences in scent profiles at the species and ecotype level that corresponded to different pollinators and were thus suggestive of pollinator-mediated selection.

CONCLUSIONS

Scent variation was greater than expected and phylogeny was more important than pollinator-mediated selection in predicting the composition of floral scents of oil-secreting orchids, despite the specialized nature of the pollinator reward system.

Pitchers of Nepenthes rajah collect faecal droppings from both diurnal and nocturnal small mammals and emit fruity odour

The pitchers of Nepenthes rajah, a montane carnivorous plant species from Borneo, are large enough to capture small vertebrates such as rats or lizards, which occasionally drown therein. The interactions of N. rajah with vertebrates, however, are poorly understood, and the potential mechanisms that lure vertebrates to the pitchers are largely unknown. We observed frequent visits (average: one visit per 4.2 h) of both the diurnal tree shrew Tupaia montana and the nocturnal rat Rattus baluensis to pitchers by infrared sensor camera and video recording. Both mammalian species often licked the inner surface of the pitcher lid, which harbours numerous exudate-producing glands. Analysis of volatiles extracted from the secretions of the pitcher lids by gas chromatography coupled to mass spectrometry (GC/MS) revealed 44 volatile compounds, including hydrocarbons, alcohols, esters, ketones and sulphur-containing compounds, which are commonly present in sweet fruit and flower odours. The faeces of small mammals were repeatedly observed inside the pitcher, whereas we found the body of only one Tupaia montana drowned in the 42, vital and reasonably large, surveyed pitchers. Our findings suggest that the N. rajah pitcher makes use of the perceptual biases of rats and tree shrews by emitting volatiles known from fruits. The profits that the plant obtains from the repeated visits of two small mammals, together with the provision of exudates for the mammals, comprise an exceptional case of plant–vertebrate interaction.

Mammal pollinators lured by the scent of a parasitic plant

To communicate with animals, plants use signals that are distinct from their surroundings. Animals generally learn to use these signals through associative conditioning; however, signals are most effective when they elicit innate behavioural responses. Many plant species have flowers specialized for pollination by ground-dwelling mammals, but the signals used to attract these pollinators have not been elucidated. Here, we demonstrate the chemical basis for attraction of mammal pollinators to flowers of the dioecious parasitic plant Cytinus visseri (Cytinaceae). Two aliphatic ketones dominate the scent of this species; 3-hexanone, which elicits strong innate attraction in rodents, and 1-hexen-3-one, which repels them in isolation, but not in combination with 3-hexanone. The aliphatic ketone-dominated scent of C. visseri contrasts with those of insect-pollinated plants, which are typically dominated by terpenoids, aromatic or non-ketone aliphatic compounds. 3-hexanone is also known from some bat-pollinated species, suggesting independent evolution of plant signals in derived, highly specialized mammal-pollination systems.

Lack of generalization of object discrimination between spatial contexts by a bat

Discrimination and generalization are important elements of cognition in the daily lives of animals. Nectar-feeding bats detect flowers by olfaction and probably vision, but also use echolocation and echo-perception of flowers in immediate target surroundings. The echo received from an interference-rich flower corolla is a function of a bat's own relative position in space. This raises the question how easily a free-flying bat will generalize an echo stimulus from a learning situation to a new spatial context where differences in relative flight approach trajectories may lead to an unfamiliar spectral composition of the self-generated echoes. We trained free-flying Glossophaga soricina in echoacoustic discrimination in a two-alternative forced-choice (2-AFC) paradigm at location A. We then tested at location B for spontaneous transfer of discrimination ability. Bats did not spontaneously transfer the discrimination ability acquired at A to location B. This lack of spontaneous generalization may have been caused by factors of the underlying learning mechanisms. 2-AFC tasks may not be representative of the natural foraging behaviour of flower-visiting bats. In contrast to insect-eating bats that constantly evaluate the environment to detect unpredictable prey, the spatial stability of flowers may allow flower visitors to rely on spatial memory to guide foraging. The 2-AFC task requires the disregard (learned irrelevance) of salient spatial location cues that are different at each new location. In Glossophaga, a conjunction between spatial context and 2-AFC discrimination learning may have inhibited the transfer of learned irrelevance of spatial location in the 2-AFC task to new spatial locations. Alternatively, the bats may have learnt the second discrimination task completely anew, and were faster only because of an acquired learning set. We suggest a dissociation between 2-AFC task acquisition and novel object discrimination learning to resolve the issue.

Three 1-thio-β-d-glucopyranosides from the seeds of Afrostyrax lepidophyllus Mildbr

Three new 1-thioglycosides namely methylthiomethyl 1-thio-beta-D-glucopyranoside (Afrostyraxthioside A), methylsulfonylmethyl 1-thio-beta-D-glucopyranoside (Afrostyraxthioside B) and methylsulfonylmethylthiomethyl 1-thio-beta-D-glucopyranoside (Afrostyraxthioside C) were isolated from the seeds of Afrostyrax lepidophyllus Mildbr. Their structures were mainly elucidated by using one- and two-dimensional NMR and mass spectroscopies and also by an efficient one-step synthesis. Moreover, Afrostyraxthiosides A, B and C constitute a new subclass of 1-thioglycosides isolated from natural sources.

The chemical nature of fetid floral odours in stapeliads (Apocynaceae-Asclepiadoideae-Ceropegieae)

By emitting strong fetid scents, sapromyiophilous flowers mimic brood and food sites of flies to attract them as pollinators. To date, intensive comparative scent analyses have been restricted to sapromyiophilous Araceae. Here, we analysed flower volatiles of fetid stapeliads to improve our understanding of the floral biology of fly pollinated species, and to learn whether mimicry types comparable to those found in Araceae exist. Floral volatiles of 15 species out of 11 genera within the Asclepiadoideae-Ceropegieae-Stapeliinae were collected via headspace adsorption and thermal desorption and analysed by gas chromatography-mass spectometry (GC-MS). Data were analysed using CNESS-NMDS statistics. Sapromyiophilous stapeliads are highly diverse in their scent composition, in which sulphur compounds, benzenoids, fatty acid derivatives or nitrogen-containing compounds dominate. Four groups are evident: species with high p-cresol content but low amounts of polysulphides (herbivore faeces mimicry); species with mainly polysulphides and low amounts of p-cresol (carnivore/omnivore faeces or carcass mimicry); species with high amounts of heptanal and octanal (carnivore/omnivore faeces or carcass mimicry); and species with hexanoic acid (urine mimicry). Considering the findings in the unrelated Araceae, our results support the universality of different mimicry types that are obviously subsumed under the sapromyiophilous syndrome.

The Odour, the Animal and the Plant

A review of the literature is presented that gives a background to the human sense of smell, then the importance of learnt and innate olfactory cues in animal behaviour. Some possible roles for natural products chemists interested in the interaction between animals and plants are discussed.