Stefan Dötterl

Spatial fragrance patterns in flowers of Silene latifolia: Lilac compounds as olfactory nectar guides?

Floral odour can differ qualitatively and quantitatively between different parts of the flowers, and these spatial fragrance patterns within the flowers can be used by pollinators for orientation on flowers. Here we present results of spatial fragrance patterns within flowers of the dioecious Silene latifolia (Caryophyllaceae). Volatiles were collected and analysed using a highly sensitive dynamic headspace method, which allows dramatically reducing the sample time. From all flower parts, especially the petals and the anthophore emitted the typical flower volatiles of S. latifolia. However, compounds emitted from the petals differed from compounds emitted by the anthophore. The anthophore emitted the monoterpenoids lilac aldehydes and alcohols, whereas, all other typical scent compounds (e.g. benzoids, other monoterpenoids) were emitted by the petals. Lilac aldehydes are known to be behaviourally very attractive for noctuid moths, and they may serve as nectar guides in S. latifolia.

1,4-Dimethoxybenzene, a Floral Scent Compound in Willows that Attracts an Oligolectic Bee

Many bees are oligolectic and collect pollen for their larvae only from one particular plant family or genus. Here, we identified flower scent compounds of two Salix species important for the attraction of the oligolectic bee Andrena vaga, which collects pollen only from Salix. Flower scent was collected by using dynamic-headspace methods from Salix caprea and S. atrocinerea, and the samples were subsequently analyzed by coupled gas chromatographic–electroantennographic detection (GC-EAD) to detect possible attractants of A. vaga. EAD active compounds were identified by gas chromatography coupled to mass spectrometry. Both Salix species had relatively similar scent profiles, and the antennae of male and female bees responded to at least 16 compounds, among them different benzenoids as well as oxygenated monoterpenoids and sesquiterpenoids. The strongest antennal responses were triggered by 1,4-dimethoxybenzene, and in field bioassays, this benzenoid attracted females of A. vaga at the beginning of its flight period, but not at the end.

THE EVOLUTION OF FLORAL SCENT AND OLFACTORY PREFERENCES IN POLLINATORS: COEVOLUTION OR PRE‐EXISTING BIAS?

Coevolution is thought to be a major factor in shaping plant–pollinator interactions. Alternatively, plants may have evolved traits that fitted pre‐existing preferences or morphologies in the pollinators. Here, we test these two scenarios in the plant family of Araceae and scarab beetles (Coleoptera, Scarabaeidae) as pollinators. We focused on floral volatile organic compounds (VOCs) and production/detection of VOCs by scarab beetles. We found phylogenetic structure in the production/detection of methoxylated aromatics in scarabs, but not plants. Within the plants, most of the compounds showed a well‐supported pattern of correlated evolution with scarab‐beetle pollination. In contrast, the scarabs showed no correlation between VOC production/detection and visitation to Araceae flowers, with the exception of the VOC skatole. Moreover, many VOCs were found in nonpollinating beetle groups (e.g., Melolonthinae) that are ancestors of pollinating scarabs. Importantly, none of the tested VOCs were found to have originated in pollinating taxa. Our analysis indicates a Jurassic origin of VOC production/detection in scarabs, but a Cretaceous/Paleocene origin of floral VOCs in plants. Therefore, we argue against coevolution, instead supporting the scenario of sequential evolution of floral VOCs in Araceae driven by pre‐existing bias of pollinators.

Floral Odors of Silene otites: Their Variability and Attractiveness to Mosquitoes

Inflorescence scent samples from nine populations of dioecious Silene otites, a plant pollinated by moths and mosquitoes, were collected by dynamic headspace extraction. Sixty-three scent samples were analyzed by gas chromatography–mass spectrometry. Out of 38 found, 35 compounds were identified, most of which were monoterpenoids, fatty acid derivatives, and benzenoids. Phenyl acetaldehyde was the most dominant compound in the majority of samples. The variability in scent composition was high, and population and sex differences were found. Nevertheless, wind tunnel experiments proved similar attraction of Culex pipiens pipiens biotype molestus mosquitoes to the inflorescence odor of S. otites of different populations, indicating that different blends are similarly attractive to mosquitoes. The electrophysiological responses of mosquitoes to the 12 most common and abundant odor compounds of S. otites differed. Linalool oxide (furanoid) and linalool evoked the strongest responses in male and female mosquitoes, and (Z)-3-hexenyl acetate was strongly active in females. Medium responses were evoked in males by (Z)-3-hexenyl acetate, in females by benzaldehyde and methyl salicylate, and in both sexes by lilac aldehyde, lilac alcohol, and linalool oxide (pyranoid).

Chemical composition of anther volatiles in Ranunculaceae: genera-specific profiles in Anemone, Aquilegia, Caltha, Pulsatilla, Ranunculus, and Trollius species

Anther volatiles of 12 Ranunculaceae species distributed in six genera (Anemone, Aquilegia, Caltha, Pulsatilla, Ranunculus, and Trollius) were investigated by thermal desorption of anthers in quartz microvials inserted into a modified injector. Chemical analysis (GC-MS) yielded a total of 116 compounds from which 103 compounds could be identified. A great diversity of compounds was observed, including aliphatic compounds, aromatics, mono- and sesquiterpenoids, and nitrogen-bearing compounds. Intraspecific variation in the chemical profiles was significantly lower than interspecific variation. Eight compounds explained 96.1% of the observed total variation between the taxa: protoanemonin, octanal, (E,E)-α-farnesene, 2-phenyl ethanol, pentadecane, α-muurolene, phenyl acetaldehyde, and linalool oxide (pyranoid) were either present only in specific taxa or varied greatly in their relative amount between the taxa. An analysis of the scent data using the chord-normalized expected species shared (CNESS) distances of chemical profiles of the species, followed by visualization of the data with nonmetric multidimensional scaling (NMDS) showed that most species belonging to the same genus have similar chemical compositions. The differences in the chemical composition of anther volatiles are discussed with respect to the taxonomy and pollination biology of the species.

Disease Status and Population Origin Effects on Floral Scent: Potential Consequences for Oviposition and Fruit Predation in A Complex Interaction Between A Plant, Fungus, and Noctuid Moth

In the Silene latifolia–Hadena bicruris nursery pollination system, the Hadena moth is both pollinator and seed predator of its host plant. Floral scent, which differs among S. latifolia individuals and populations, is important for adult Hadena to locate its host. However, the success of moth larvae is strongly reduced if hosts are infected by the anther smut fungus Microbotryum violaceum, a pathogen that is transmitted by flower visitors. There were no qualitative differences between the scent of flowers from healthy and diseased plants. In addition, electroantennographic measurements showed that Hadena responded to the same subset of 19 compounds in samples collected from healthy and diseased plants. However, there were significant quantitative differences in scent profiles. Flowers from diseased plants emitted both a lower absolute amount of floral scent and had a different scent pattern, mainly due to their lower absolute amount of lilac aldehyde, whereas their amount of (E)-β-ocimene was similar to that in healthy flowers. Dual choice behavioral wind tunnel tests using differently scented flowers confirmed that moths respond to both qualitative and quantitative aspects of floral scent, suggesting that they could use differences in floral scent between healthy and infected plants to discriminate against diseased plants. Population mean fruit predation rates significantly increased with population mean levels of the emission rates of lilac aldehyde per flower, indicating that selection on floral scent compounds may not only be driven by effects on pollinator attraction but also by effects on fruit predation. However, variation in mean emission rates of scent compounds per flower generally could not explain the higher fruit predation in populations originating from the introduced North American range compared to populations native to Europe.

Hawaiian ant—flower networks: nectar-thieving ants prefer undefended native over introduced plants with floral defenses

Ants are omnipresent in most terrestrial ecosystems, and plants have responded to their dominance by evolving traits that either facilitate positive interactions with ants or reduce negative ones. Because ants are generally poor pollinators, plants often protect their floral nectar against ants. Ants were historically absent from the geographically isolated Hawaiian archipelago, which harbors one of the most endemic floras in the world. We hypothesized that native Hawaiian plants lack floral features that exclude ants and therefore would be heavily exploited by introduced, invasive ants. To test this hypothesis, ant–flower interactions involving co-occurring native and introduced plants were observed in 10 sites on three Hawaiian Islands. We quantified the residual interaction strength of each pair of ant–plant species as the deviation of the observed interaction frequency from a null-model prediction based on available nectar sugar in a local plant community and local ant activity at sugar baits. As pred...

Inter- and Intraspecific Variation in Floral Scent in the Genus Salix and its Implication for Pollination

The floral scent composition of 32 European and two Asian Salix L. species (Salicaceae) was analyzed. Intra- and interspecific variation was compared for a subset of 8 species. All Salix species are dioecious and floral scent was collected from both male and female individuals by using a dynamic headspace MicroSPE method, and analyzed by GC-MS. A total of 48 compounds were detected, most of them being isoprenoids and benzenoids. Commonly occurring compounds included trans-β-ocimene, cis-β-ocimene, benzaldehyde, d-limonene, α-pinene, cis-3-hexenyl aceatate, linalool, 1,4-dimethoxybenzene, and β-pinene. Two compounds, 1,4-dimethoxybenzene and trans-β-ocimene, were responsible for most of the interspecific variation. In a subset of eight extensively sampled species, six had a characteristic floral scent composition; half of the pairwise species comparisons confirmed significant differences. In three of these eight species, intraspecific variability could be explained by sex differences. Variation in Salix floral scent may provide specific signals that guide pollinators and thus contribute to the reproductive isolation of compatible and cooccurring species.

Flower Scent of Floral Oil-Producing Lysimachia punctata as Attractant for the Oil-Bee Macropis fulvipes

Most flowers offer nectar and/or pollen as a reward for pollinators. However, some plants are known to produce mostly fatty oil in the flowers, instead of nectar. This oil is exclusively collected by specialized oil-bees, the pollinators of the oil-plants. Little is known about chemical communication in this pollination system, especially how the bees find their hosts. We collected the floral and vegetative scent emitted by oil-producing Lysimachia punctata by dynamic headspace, and identified the compounds by gas chromatography coupled to mass spectrometry. Thirty-six compounds were detected in the scent samples, several of which were flower-specific. Pentane extracts of flowers and floral oil were tested on Macropis fulvipes in a biotest. Flower and oil extracts attracted the bees, and some of the compounds identified are seldom found in the floral scent of other plants; these may have been responsible for the attraction of the bees.

The role of volatile organic compounds, morphology and pigments of globeflowers in the attraction of their specific pollinating flies

• Floral scents and visual cues of the globeflower Trollius europaeus may play a key role in the attraction of Chiastocheta flies, involved in a highly specific nursery pollination mutualism. • Here, headspace collection and GC-MS were used to identify and quantify the volatile organic compounds emitted by the globeflower. • Scents are produced in three different floral parts by four structures: secretory glands and flat epidermis cells in the abaxial sepal epidermis, conical cells in the adaxial sepal epidermis, and pollen. The blend is made up of 16 compounds commonly found in floral scents. Geographical variation among populations is low compared with variation amongst individuals within populations. Electroantenno-graphic analyses revealed that six compounds emitted by both anthers and sepals are detected by Chiastocheta flies. Removing the anthers hidden inside the globe from flowers in the field decreased the number of fly visits to globeflowers. • A multivariate analysis of the effect of several floral traits on pollinator visitation rate conducted in the field showed that both floral scents and visual flower cues play a role in pollinator attraction. However, their relative roles and the intensity of the selective pressures exerted on floral traits by pollinators appear to vary in time and space.