Floral scent emitted by white and coloured morphs in orchids

The road less taken: Dihydroflavonol 4-reductase inactivation and delphinidin anthocyanin loss underpins a natural intraspecific flower colour variation

Visual cues are of critical importance for the attraction of animal pollinators, however, little is known about the molecular mechanisms underpinning intraspecific floral colour variation. Here, we combined comparative spectral analysis, targeted metabolite profiling, multi-tissue transcriptomics, differential gene expression, sequence analysis and functional analysis to investigate a bee-pollinated orchid species, Glossodia major with common purple- and infrequent white-flowered morphs. We found uncommon and previously unreported delphinidin-based anthocyanins responsible for the conspicuous and pollinator-perceivable colour of the purple morph and three genetic changes underpinning the loss of colour in the white morph - (1) a loss-of-function (LOF; frameshift) mutation affecting dihydroflavonol 4-reductase (DFR1) coding sequence due to a unique 4-bp insertion, (2) specific downregulation of functional DFR1 expression and (3) the unexpected discovery of chimeric Gypsy transposable element (TE)-gene (DFR) transcripts with potential consequences to the genomic stability and post-transcriptional or epigenetic regulation of DFR. This is one of few known cases where regulatory changes and LOF mutation in an anthocyanin structural gene, rather than transcription factors, are important. Furthermore, if TEs prove to be a frequent source of mutation, the interplay between environmental stress-induced TE evolution and pollinator-mediated selection for adaptive colour variation may be an overlooked mechanism maintaining floral colour polymorphism in nature.

The volatile chemistry of orchid pollination

Covering: up to September 2022Orchids are renowned not only for their diversity of floral forms, but also for their many and often highly specialised pollination strategies. Volatile semiochemicals play a crucial role in the attraction of a wide variety of insect pollinators of orchids. The compounds produced by orchid flowers are as diverse as the pollinators they attract, and here we summarise some of the chemical diversity found across orchid taxa and pollination strategies. We focus on compounds that have been experimentally demonstrated to underpin pollinator attraction. We also highlight the structural elucidation and synthesis of a select subset of important orchid pollinator attractants, and discuss the ecological significance of the discoveries, the gaps in our current knowledge of orchid pollination chemistry, and some opportunities for future research in this field.

Traditional, Therapeutic Uses and Phytochemistry of Terrestrial European Orchids and Implications for Conservation

The Orchidaceae family accounts for about 28,000 species, and most of them are mentioned in the folk medicine of nations around the world. The use of terrestrial orchids in European and Mediterranean regions has been reported since ancient times, but little information is available on their medicinal properties, as well as on their phytochemicals and biological activities. However, plant collection for human use is still listed as one of the main threats for terrestrial orchids, alongside other menacing factors such as wrong habitat management and disturbance to symbionts, such as pollinators and mycorrhizal fungi. Therefore, the primary aim of this review was to resume and discuss available information regarding the past and current popular uses of European orchids. We then grouped phytochemical data to evaluate the presence of bioactive compounds of pharmacological relevance, and we discussed whether these could support the therapeutic employment of the different organs. Finally, we briefly debated the sustainability of orchid utilizations, considering the different threatening factors and conservation actions including plant propagation methods.

Mechanisms of flower coloring and eco-evolutionary implications of massive blooming events in the Atacama Desert

The Atacama Desert, one of the driest places on earth, holds a rich biodiversity that becomes most appreciable in years when unusual rainfall accumulation triggers a phenomenon of explosive development of ephemeral herbaceous and woody desert species known as “desierto florido” or “blooming desert.” Despite the scientific importance of this unique phenomenon only few studies have addressed the mechanisms of flower phenotypic divergence under the fluctuating environment provided by this recurrent event. We investigated the mechanisms of floral color diversity in Cistanthe longiscapa (Montiaceae), a dominant species across the ephemeral blooming landscape of Atacama Desert. Our analyses show that the variation in colors of C. longiscapa flowers result from petals containing betalain pigments with different absorption spectra. The different pigment composition of petals causes flower color differences in the visible and ultraviolet (UV) range of the spectrum. Through color vision models we show that C. longiscapa flowers are highly polymorphic in their color appearance for insect pollinators. Our results highlight the variable nature in flower color of C. longiscapa varieties blooming simultaneously in a geographical restricted area. Given the importance of color in attracting floral visitors, the observed color variability could contribute to increased cross pollination in extreme desert conditions, while accounting for complex and fluctuating histories of plant-pollinator interactions.

Floral Scents of a Deceptive Plant Are Hyperdiverse and Under Population-Specific Phenotypic Selection

Floral scent is a key mediator in plant-pollinator interactions. However, little is known to what extent intraspecific scent variation is shaped by phenotypic selection, with no information yet in deceptive plants. In this study, we collected inflorescence scent and fruit set of the deceptive moth fly-pollinated Arum maculatum L. (Araceae) from six populations north vs. five populations south of the Alps, accumulating to 233 samples in total, and tested for differences in scent, fruit set, and phenotypic selection on scent across this geographic barrier. We recorded 289 scent compounds, the highest number so far reported in a single plant species. Most of the compounds occurred both north and south of the Alps; however, plants of the different regions emitted different absolute and relative amounts of scent. Fruit set was higher north than south of the Alps, and some, but not all differences in scent could be explained by differential phenotypic selection in northern vs. southern populations. This study is the first to provide evidence that floral scents of a deceptive plant are under phenotypic selection and that phenotypic selection is involved in shaping geographic patterns of floral scent in such plants. The hyperdiverse scent of A. maculatum might result from the imitation of various brood substrates of its pollinators.

Extraction and Identification of Volatile Organic Compounds Emitted by Fragrant Flowers of Three Tillandsia Species by HS-SPME/GC-MS

Numerous volatile organic compounds (VOCs) with a large chemical diversity are emitted by plant flowers. They play an important role in the ecology of plants, such as pollination, defense, adaptation to their environment, and communication with other organisms. The Tillandsia genus belongs to the Bromeliaceae family, and most of them are epiphytes. The aromatic profile of the Tillandsia genus is scarcely described. In this study, we use the headspace solid phase microextraction (HS-SPME) coupled with gas chromatography combined with mass spectrometry (GC-MS) method developed in our laboratory to explore the chemical diversity of the VOCs of fragrant flowers of three species of the genus Tillandsia. We were able to identify, for the first time, 66 volatile compounds (monoterpenes, sesquiterpenes, phenylpropanoids, and other compounds). We identified 30 compounds in T. xiphioides, 47 compounds in T. crocata, and 43 compounds in T. caliginosa. Only seven compounds are present in all the species studied. Comparison of the volatile compounds profiles by principal component analysis (PCA) between T. xiphoides, T. crocata, and T. caliginosa species showed a clear difference in the floral emissions of the studied species. Moreover, floral VOCs profiles allowed to differentiate two forms of T. xiphioides and of T. crocata.

Transcriptome-Based WGCNA Analysis Reveals Regulated Metabolite Fluxes between Floral Color and Scent in Narcissus tazetta Flower

A link between the scent and color of Narcissus tazetta flowers can be anticipated due to their biochemical origin, as well as their similar biological role. Despite the obvious aesthetic and ecological significance of these colorful and fragrant components of the flowers and the molecular profiles of their pigments, fragrant formation has addressed in some cases. However, the regulatory mechanism of the correlation of fragrant components and color patterns is less clear. We simultaneously used one way to address how floral color and fragrant formation in different tissues are generated during the development of an individual plant by transcriptome-based weighted gene co-expression network analysis (WGCNA). A spatiotemporal pattern variation of flavonols/carotenoids/chlorophyll pigmentation and benzenoid/phenylpropanoid/ monoterpene fragrant components between the tepal and corona in the flower tissues of Narcissus tazetta, was exhibited. Several candidate transcription factors: MYB12, MYB1, AP2-ERF, bZIP, NAC, MYB, C2C2, C2H2 and GRAS are shown to be associated with metabolite flux, the phenylpropanoid pathway to the production of flavonols/anthocyanin, as well as related to one branch of the phenylpropanoid pathway to the benzenoid/phenylpropanoid component in the tepal and the metabolite flux between the monoterpene and carotenoids biosynthesis pathway in coronas. It indicates that potential competition exists between floral pigment and floral fragrance during Narcissus tazetta individual plant development and evolutionary development.

The effects of pollination, herbivory and autonomous selfing on the maintenance of flower colour variation in Silenelittorea

Intraspecific flower colour variation has been generally proposed to evolve as a result of selection driven by biotic or abiotic agents. In a polymorphic population of Silene littorea with pink- and white-flowered plants, we studied pollinators, analysed flower colour perception and tested for differences in pollinator visitation. We also experimentally analysed pollinator limitation in fruit and seed set, and the degree of autonomous selfing. The incidence of florivory and leaf herbivory was compared over 3-4 years. Silene littorea is mainly pollinated by bees and butterflies. Pollinators preferred pink flowers, which did not show pollinator limitation. On the contrary, white flowers showed pollinator limitation in fruit set. White-flowered plants had less floral display and higher levels of florivory than pink plants. Flower colour morphs of S. littorea can reproduce in the absence of pollinators by autonomous selfing, setting 20% and 12% of fruit and seeds in the pink morph and 27% and 20% in the white morph, respectively. Fruit set of white flowers produced by autonomous selfing did not differ from open-pollinated flowers. In conclusion, S. littorea is pollinated by insects of different orders that more frequently visit pink flowers, which is reflected in pollinator limitation of fruit set in white flowers. Moreover, this species has a mixed mating system in which both colour morphs can reproduce in the absence of pollinators by autonomous selfing, although white flowers mainly produce fruits by autogamy. We suggest that reproductive assurance by autonomous selfing helps to maintain flower colour polymorphism in this population.

Why Variation in Flower Color May Help Reproductive Success in the Endangered Australian Orchid Caladenia fulva

Caladenia fulva G.W. Carr (Tawny Spider-orchid) is a terrestrial Australian endangered orchid confined to contiguous reserves in open woodland in Victoria, Australia. Natural recruitment is poor and no confirmed pollinator has been observed in the last 30 years. Polymorphic variation in flower color complicates plans for artificial pollination, seed collection and ex situ propagation for augmentation or re-introduction. DNA sequencing showed that there was no distinction among color variants in the nuclear ribosomal internal transcribed spacer (ITS) region and the chloroplast trnT-trnF and matK regions. Also, authentic specimens of both C. fulva and Caladenia reticulata from the reserves clustered along with these variants, suggesting free interbreeding. Artificial cross-pollination in situ and assessment of seed viability further suggested that no fertility barriers existed among color variants. Natural fruit set was 15% of the population and was proportional to numbers of the different flower colors but varied with orchid patch within the population. Color modeling on spectral data suggested that a hymenopteran pollinator could discriminate visually among color variants. The similarity in fruiting success, however, suggests that flower color polymorphism may avoid pollinator habituation to specific non-rewarding flower colors. The retention of large brightly colored flowers suggests that C. fulva has maintained attractiveness to foraging insects rather than evolving to match a scarce unreliable hymenopteran sexual pollinator. These results suggest that C. fulva should be recognized as encompassing plants with these multiple flower colors, and artificial pollination should use all variants to conserve the biodiversity of the extant population.

What pollinators see does not match what they smell: Absence of color-fragrance association in the deceptive orchid Ionopsis utricularioides

Many deceptive orchids present variation in floral color and fragrance. This might be advantageous for the plant, as it can disturb the associative avoidance learning of pollinators, promoting more visits to the flowers. Some studies have shown that color and fragrance can be correlated in polymorphic deceptive orchids, but these studies employed color traits based on the human visual system and not the visual perception of pollinators. Thus, we investigated the composition of the floral fragrance of Ionopsis utricularioides (Sw.) Lindl., a polymorphic deceptive orchid, and analyzed possible correlations with the floral color as seen by bees, Apis mellifera L. and Melipona quadrifasciata Lepeletier, using the color hexagon model. We found high color and fragrance intraspecific variation, as expected for deceptive species. However, we found no color-fragrance association in individuals, either by comparing fragrance profiles with the color variable saturation or by comparing them with the placement of individuals in the color hexagon for both bee species. This lack of correlation contradicts the biochemical pathway hypothesis, which proposes that associations between floral color and scent in polymorphic flowers arise from shared biochemical pathways. However, a complete absence of correlation between floral signals is consistent with selection arising through pollinator cognitive ecology. Lack of correlation would increase the floral variability perceived by bees, given their multimodal learning, and this variability could disrupt avoidance learning of deceptive flowers, thus enhancing the efficacy of the plant's deceptive pollination mechanism.

Floral trait differentiation in Anacamptis coriophora: Phenotypic selection on scents, but not on colour

Current divergent selection may promote floral trait differentiation among conspecific populations in flowering plants. However, whether this applies to complex traits such as colour or scents has been little studied, even though these traits often vary within species. In this study, we compared floral colour and odour as well as selective pressures imposed upon these traits among seven populations belonging to three subspecies of the widespread, generalist orchid Anacamptis coriophora. Colour was characterized using calibrated photographs, and scents were sampled using dynamic headspace extraction and analysed using gas chromatography-mass spectrometry. We then quantified phenotypic selection exerted on these traits by regressing fruit set values on floral trait values. We showed that the three studied subspecies were characterized by different floral colour and odour, with one of the two predominant floral volatiles emitted by each subspecies being taxon-specific. Plant size was positively correlated with fruit set in most populations, whereas we found no apparent link between floral colour and female reproductive success. We detected positive selection on several taxon-specific compounds in A. coriophora subsp. fragrans, whereas no selection was found on floral volatiles of A. coriophora subsp. coriophora and A. coriophora subsp. martrinii. This study is one of the first to document variation in phenotypic selection exerted on floral scents among conspecific populations. Our results suggest that selection could contribute to ongoing chemical divergence among A. coriophora subspecies.

Characterization and Antioxidant Activity of Essential Oil of Four Sympatric Orchid Species

The volatile fractions from fresh inflorescences of naturally growing orchids Anacamptis coriophora (L.) R. M. Bateman, Pridgeon & M. W. Chase subsp. fragrans (Pollini), Anacamptis pyramidalis (L.) R. Ophrys holosericea (Burm.) Greuter and Serapias vomeracea (Burm. f.) B. were isolated by steam distillation and analyzed by GC/FID and GC/MS. Saturated hydrocarbons were quantified as the major constituents of the volatile fraction (47.87–81.57% of the total essential oil), of which long-chain monounsaturated hydrocarbons accounted from 9.20% to 32.04% of the total essential oil. Double bond position in linear alkenes was highlighted by dimethyl disulfide derivatization and MS fragmentation. Aldehydes (from 3.45 to 18.18% of the total essential oil), alcohols (from 0.19% to 13.48%), terpenes (from 0.98 to 2.50%) and acids (0.30 to 2.57%) were also detected. These volatiles compounds may represent a particular feature of these plant species, playing a critical role in the interaction with pollinators. DPPH assay evaluating the antioxidant activity of the essential oils was carried out, showing a dose-dependent antioxidant activity.

Does size really matter? A comparative study on floral traits in orchids with two different pollination strategies

The lock and key hypothesis assumes that male and female genitalia match in a unique system to prevent interspecific crosses. This hypothesis is largely investigated in animals, while there is a distinct lack of studies on plants. Nevertheless, we expect the lock and key hypothesis could apply to plants with complex floral morphologies, such as orchids. Here we apply a comparative approach to examine the variation of floral functional traits in food- and sex-deceptive orchids. To understand if a specific deception strategy is related to a specific variation in floral traits evaluated the variation in sterile and fertile traits among species and subsequently examined the correlations between male and female reproductive organs of the same species with the aim of investigating the role of the lock and key hypothesis in deceptive orchids. Our results show that the functional morphology of fertile traits plays a pivotal role in limiting gene flow in species that grow in sympatry. In particular, it was observed that the Reproductive Standardisation Index (RSI) is significantly different in the two pollination strategies and that the correlation between pollinarium length and stigmatic cavity length is stronger in food-deceptive species when compared to the sex-deceptive species. These results reveal that the lock and key hypothesis contributes to maintain boundaries in plants with very complex floral morphology.

Deceptive strategy in Dactylorhiza orchids: multidirectional evolution of floral chemistry

BACKGROUND AND AIMS

The deception strategies of orchids remain poorly understood, especially in regard to the chemical compounds emitted from their flowers and their interaction with various taxonomic groups of pollinators. We investigated the phylogenetic relationships and compared the variation of floral chemical compounds between food-deceptive Dactylorhiza taxa (D. incarnata var. incarnata and D. incarnata var. ochroleuca, D. fuchsii and D. majalis) from populations in north-eastern Poland. We propose a model of the evolution of deception based on floral chemical signals in this genus.

METHODS

A Bayesian approach based on polymorphic plastid DNA (trnL, trnF and psbC-trnK), internal transcribed spacer (ITS) sequences and flow cytometry data was applied to confirm the taxonomic status of the studied orchids. We also identified and classified the pollinators and flower visitors in each Dactylorhiza population to the taxonomic level and compared our results with literature data. The chemical composition of pentane and diethyl ether extracts from the flowers was analysed by gas chromatography-mass spectrometry. Variation of the floral chemical components was visualized by non-metric multidimensional scaling based on Bray-Curtis dissimilarity.

KEY RESULTS

The genetic distinctiveness of D. incarnata, D. fuchsii and D. majalis was confirmed. No hybrids between them were found, but the chloroplast DNA (cpDNA), ITS haplotypes and flow cytometry showed genetic similarity between D. incarnata var. incarnata and D. incarnata var. ochroleuca. We determined that Apis mellifera (Hymenoptera) was the only shared pollinator of these taxa. Strangalia attenuata and Alosterna tabacicolor (Coleoptera) and Volucella pellucens and V. bombylans (Hymenoptera) were observed pollinating D. fuchsii. Visualization of the emission rates of the 61 floral chemical compounds detected from pentane extracts (mainly hydrocarbons and aldehydes) and the 51 from diethyl extracts (with abundant groups of benzenoids and non-aromatic acids) strongly differentiated D. incarnata, D. fuchsii and D. majalis, while those of the two varieties of D. incarnata (var. incarnata and var. ochroleuca) were almost identical.

CONCLUSIONS

While the genetic data clearly supported the distinct lineages of D. incarnata, D. fuchsii and D. majalis, the patterns of emission of their flower chemical compounds were more complex within the series of shared compounds (alkanes and aldehydes) and taxon-specific compounds (benzenoids and esters). Their floral bouquet can influence the sexual, social and feeding behaviour of pollinators in different ways. We observed that the floral chemical compounds attracted both shared and species-specific pollinators to Dactylorhiza, confirming the multidirectional character of floral chemical signals in these food-deceptive taxa. Reduction of species-specific pollination levels in Dactylorhiza orchid taxa may promote hybridization between them.

Morph-specific protein patterns in the femoral gland secretions of a colour polymorphic lizard

Colour polymorphism occurs when two or more genetically-based colour morphs permanently coexist within an interbreeding population. Colouration is usually associated to other life-history traits (ecological, physiological, behavioural, reproductive …) of the bearer, thus being the phenotypic marker of such set of genetic features. This visual badge may be used to inform conspecifics and to drive those decision making processes which may contribute maintaining colour polymorphism under sexual selection context. The importance of such information suggests that other communication modalities should be recruited to ensure its transfer in case visual cues were insufficient. Here, for the first time, we investigated the potential role of proteins from femoral gland secretions in signalling colour morph in a polymorphic lizard. As proteins are thought to convey identity-related information, they represent the ideal cues to build up the chemical modality used to badge colour morphs. We found strong evidence for the occurrence of morph-specific protein profiles in the three main colour-morphs of the common wall lizard, which showed both qualitative and quantitative differences in protein expression. As lizards are able to detect proteins by tongue-flicking and vomeronasal organ, this result support the hypothesis that colour polymorphic lizards may use a multimodal signal to inform about colour-morph.

Identification of Floral Scent Profiles in Bearded Irises

Bearded irises are ornamental plants with distinctive floral fragrance grown worldwide. To identify the floral scent profiles, twenty-seven accessions derived from three bearded iris, including Iris. germanica, I. pumila and I. pallida were used to investigate the composition and relative contents of floral scent components by headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC-MS). A total of 219 floral scent components were detected in blooming flowers. The scent profile varied significantly among and within the three investigated species. Principal component analysis (PCA) indicated that terpenes, alcohols and esters contributed the most to the floral scent components and 1-caryophyllene, linalool, citronellol, methyl cinnamate, β-cedrene, thujopsene, methyl myristate, linalyl acetate, isosafrole, nerol, geraniol were identified as the major components. In a hierarchical cluster analysis, twenty-seven accessions could be clustered into six different groups, most of which had representative scent components such as linalool, citronellyl acetate, thujopsene, citronellol, methyl cinnamate and 1-caryophyllene. Our findings provide a theoretical reference for floral scent evaluation and breeding of bearded irises.

Genome-wide researches and applications on Dendrobium

This review summarizes current knowledge of chromosome characterization, genetic mapping, genomic sequencing, quality formation, floral transition, propagation, and identification in Dendrobium. The widely distributed Dendrobium has been studied for a long history, due to its important economic values in both medicine and ornamental. In recent years, some species of Dendrobium and other orchids had been reported on genomic sequences, using the next-generation sequencing technology. And the chloroplast genomes of many Dendrobium species were also revealed. The chromosomes of most Dendrobium species belong to mini-chromosomes, and showed 2n = 38. Only a few of genetic studies were reported in Dendrobium. After revealing of genomic sequences, the techniques of transcriptomics, proteomics and metabolomics could be employed on Dendrobium easily. Some other molecular biological techniques, such as gene cloning, gene editing, genetic transformation and molecular marker developing, had also been applied on the basic research of Dendrobium, successively. As medicinal plants, insights into the biosynthesis of some medicinal components were the most important. As ornamental plants, regulation of flower related characteristics was the most important. More, knowledge of growth and development, environmental interaction, evolutionary analysis, breeding of new cultivars, propagation, and identification of species and herbs were also required for commercial usage. All of these studies were improved using genomic sequences and related technologies. To answer some key scientific issues in Dendrobium, quality formation, flowering, self-incompatibility and seed germination would be the focus of future research. And genome related technologies and studies would be helpful.

Biosynthetic and Functional Color-Scent Associations in Flowers of Papaver nudicaule and Their Impact on Pollinators

Despite increasing evidence for biosynthetic connections between flower pigments and volatile compounds, examples of such relationships in polymorphic plant species remains limited. Herein, color-scent associations in flowers from Papaver nudicaule (Papaveraceae) have been investigated. The spectral reflectance and scent composition of flowers of four color cultivars was determined. We found that pigments and volatiles occur in specific combinations in flowers of P. nudicaule. The presence of indole in the bouquets is strongly associated with the occurrence of yellow pigments called nudicaulins, for which indole is one of the final biosynthetic precursors. Whereas yellow flowers emit an excess of indole, orange flowers consume it during nudicaulin production and lack the substance in their bouquet. By using the honeybee, Apis mellifera, evaluations were made on how color and scent affect the discrimination of these flowers by pollinators. Honeybees were able to discriminate artificial odor mixtures resembling those of the natural flower odors. Bees trained with stimuli combining colors and odors showed an improved discrimination performance. The results indicate that the indole moiety of nudicaulins and emitted indole might be products of the same biochemical pathway. We propose that conserved pathways account for the evolution of color-scent associations in P. nudicaule and that these associations positively affect flower constancy of pollinators.

Current Challenges in Plant Eco-Metabolomics

The relatively new research discipline of Eco-Metabolomics is the application of metabolomics techniques to ecology with the aim to characterise biochemical interactions of organisms across different spatial and temporal scales. Metabolomics is an untargeted biochemical approach to measure many thousands of metabolites in different species, including plants and animals. Changes in metabolite concentrations can provide mechanistic evidence for biochemical processes that are relevant at ecological scales. These include physiological, phenotypic and morphological responses of plants and communities to environmental changes and also interactions with other organisms. Traditionally, research in biochemistry and ecology comes from two different directions and is performed at distinct spatiotemporal scales. Biochemical studies most often focus on intrinsic processes in individuals at physiological and cellular scales. Generally, they take a bottom-up approach scaling up cellular processes from spatiotemporally fine to coarser scales. Ecological studies usually focus on extrinsic processes acting upon organisms at population and community scales and typically study top-down and bottom-up processes in combination. Eco-Metabolomics is a transdisciplinary research discipline that links biochemistry and ecology and connects the distinct spatiotemporal scales. In this review, we focus on approaches to study chemical and biochemical interactions of plants at various ecological levels, mainly plant⁻organismal interactions, and discuss related examples from other domains. We present recent developments and highlight advancements in Eco-Metabolomics over the last decade from various angles. We further address the five key challenges: (1) complex experimental designs and large variation of metabolite profiles; (2) feature extraction; (3) metabolite identification; (4) statistical analyses; and (5) bioinformatics software tools and workflows. The presented solutions to these challenges will advance connecting the distinct spatiotemporal scales and bridging biochemistry and ecology.

Volatiles from the fungal microbiome of the marine sponge Callyspongia cf. flammea

The volatiles emitted by five fungal strains previously isolated from the marine sponge Callyspongia cf. flammea were captured with a closed-loop stripping apparatus (CLSA) and analyzed by GC-MS. Besides several widespread compounds, a series of metabolites with interesting bioactivities were found, including the quorum sensing inhibitor protoanemonin, the fungal phytotoxin 3,4-dimethylpentan-4-olide, and the insect attractant 1,2,4-trimethoxybenzene. In addition, the aromatic polyketides isotorquatone and chartabomone that are both known from Eucalyptus and a new O-desmethyl derivative were identified. The biosynthesis of isotorquatone was studied by feeding experiments with isotopically labeled precursors and its absolute configuration was determined by enantioselective synthesis of a reference compound. Bioactivity testings showed algicidal activity for some of the identified compounds, suggesting a potential ecological function in sponge defence.

Multivariate Analysis of Multiple Datasets: a Practical Guide for Chemical Ecology

Chemical ecology has strong links with metabolomics, the large-scale study of all metabolites detectable in a biological sample. Consequently, chemical ecologists are often challenged by the statistical analyses of such large datasets. This holds especially true when the purpose is to integrate multiple datasets to obtain a holistic view and a better understanding of a biological system under study. The present article provides a comprehensive resource to analyze such complex datasets using multivariate methods. It starts from the necessary pre-treatment of data including data transformations and distance calculations, to the application of both gold standard and novel multivariate methods for the integration of different omics data. We illustrate the process of analysis along with detailed results interpretations for six issues representative of the different types of biological questions encountered by chemical ecologists. We provide the necessary knowledge and tools with reproducible R codes and chemical-ecological datasets to practice and teach multivariate methods.

Can honey bees discriminate between floral-fragrance isomers?

Many flowering plants present variable complex fragrances, which usually include different isomers of the same molecule. As fragrance is an essential cue for flower recognition by pollinators, we ask if honey bees discriminate between floral-fragrance isomers in an appetitive context. We used the olfactory conditioning of the proboscis extension response (PER), which allows training a restrained bee to an odor paired with sucrose solution. Bees were trained under an absolute (a single odorant rewarded) or a differential conditioning regime (a rewarded vs. a non-rewarded odorant) using four different pairs of isomers. One hour after training, discrimination and generalization between pairs of isomers were tested. Bees trained under absolute conditioning exhibited high generalization between isomers and discriminated only one out of four isomer pairs; after differential conditioning, they learned to differentiate between two out of four pairs of isomers but in all cases generalization responses to the non-rewarding isomer remained high. Adding an aversive taste to the non-rewarded isomer facilitated discrimination of isomers that otherwise seemed non-discriminable, but generalization remained high. Although honey bees discriminated isomers under certain conditions, they achieved the task with difficulty and tended to generalize between them, thus showing that these molecules were perceptually similar to them. We conclude that the presence of isomers within floral fragrances might not necessarily contribute to a dramatic extent to floral odor diversity.

Understanding intraspecific variation of floral scent in light of evolutionary ecology

Background and Aims

Among the various floral traits involved in pollinator attraction and potentially under selection mediated by pollinators, floral scent/fragrance has been less investigated than other components of floral phenotype. Whether or not pollinator-mediated selection impacts floral scents depends on the heritability of scent/fragrance and the occurrence of some variation within species. Although most studies have investigated how scent varies among species, growing amounts of data are available on variation at the intraspecific level.

Methods

The results of 81 studies investigating intraspecific variation of floral scents in 132 taxa were reviewed. For each study, whether variation was found in either identity, proportion or absolute quantities of volatile organic compounds (VOCs) was recorded, as well as information with the potential to explain variation, such as methodology, plant origin or pollination biology.

Key Results

Variation was found for almost all investigated species, both among individuals (among and sometimes within populations) and within individuals across different temporal scales. Cases in which such variation is a possible result of pollinator-mediated selection were analysed, by discussing separately selection related to variation in pollinator identity/behaviour among populations or across time, deceit pollination and sex-specific selection. Not surprisingly, in many cases, pollinator-mediated selection alone does not explain the observed variation in floral scent. This led us to review current knowledge on less investigated factors, such as selection mediated by natural enemies, genetic drift and gene flow, environmental constraints, phylogenetic inertia, or biochemical constraints that could be invoked to explain scent variation.

Conclusions

This review highlights the great potential of analysing floral scent variation and including it in integrated studies of floral phenotypes. We also have identified the current gaps in our understanding of this complex signal and we propose several methodological and conceptual future directions in this research area.

Chemical Composition, Antioxidant and Cytotoxic Activities of Essential Oil of the Inflorescence of Anacamptis coriophora subsp. fragrans (Orchidaceae) from Tunisia

The chemical composition of the essential oil produced by steam distillation of the inflorescences of naturally growing Anacamptis coriophora (L.) R. M. Bateman, Pridgeon & M. W. Chase subsp. fragrans (Pollini) R. M. Bateman, Pridgeon & M. W. Chase (Orchidaceae) from Kroumiria, north-west Tunisia was studied by GC-MS, which led to the identification of 19 volatile components, representing 97% of the oil. The main constituents were methyl-( E)-p-methoxycinnamate (29.3%), 13-heptadecyn-l-ol (18.6%), 2,5-dimethoxybenzyl alcohol (14.1%) and 4-(1,1,3,3-tetramethylbutyl)-phenol (9.0%). DPPH radical scavenging revealed a weak antioxidant activity. In addition, the antiproliferative effects were evaluated on BxPC3 human pancreatic carcinoma cells and on 2008 human ovarian cancer cells showing significant effect. This is the first report of the chemical composition of essential oils obtained from A coriophora subsp. fragrans inflorescences for North Africa. Further studies are needed to understand fully the possible mechanism of action behind the cytotoxic activity of the essential oil.

Integrating Studies on Plant-Pollinator and Plant-Herbivore Interactions

Research on herbivore-induced plant defence and research on pollination ecology have had a long history of separation. Plant reproduction of most angiosperm species is mediated by pollinators, and the effects of herbivore-induced plant defences on pollinator behaviour have been largely neglected. Moreover, there is expected to be a trade-off between plant reproductive strategies and defence mechanisms. To investigate this trade-off, it is essential to study herbivore-induced plant resistance and allocation of resources by plants, within the same system, and to test if indirect plant resistance can conflict with pollinator attraction. Here, I review the key literature highlighting connection between plant defence and reproduction, and propose to exploit natural variation among plant species to assess the ecological costs of plant responses to herbivores and pollinators.