Strong Conservation of Floral Scent Composition in Two Allopatric Yuccas

Floral scent has been suggested to play a key role in the obligate pollination mutualism between yuccas and yucca moths. We analyzed floral fragrance compounds of Yucca elata with headspace collection followed by gas chromatography and mass spectrometry, and compared the odor blend with the recently characterized blend of the allopatric Yucca filamentosa. A principal component analysis based on 20 scent compounds revealed that the floral odor bouquets of Y. elata and Y. filamentosa are virtually identical. Although the two plants belong to the same section of capsular-fruited yuccas, they rely on different species of Tegeticula moths for pollination and probably have been allopatric for several million years. Yet, their floral odor blends are very similar, which may indicate that strong selection by obligate pollinators counteracts drift or divergence in this trait.     

Inter- and Intraspecific Variation in Floral Scent in the Genus <Emphasis Type="Italic">Salix</Emphasis> 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.     

Variation of Floral Scent Emission and Postpollination Changes in Individual Flowers of Ophrys sphegodes Subsp. sphegodes

We investigated the scent composition of individual flowers of Ophrys sphegodes, its alteration following pollination, and of picked flowers by day and at night. Odor samples were collected by headspace sorption and analyzed by gas chromatography and mass spectrometry. To evaluate the function of postpollination odor changes, we carried out behavioral tests on the pollinator Andrena nigroaenea with pollinated and unpollinated flowers. We identified 27 volatiles in the flower scents. Aldehydes and alkanes were most frequently found. Aldehydes were the most abundant class of compounds (40–50%). When flowers were picked, they emitted significantly lower total amounts of volatiles than unpicked flowers, and their odor bouquets were significantly different. Comparison of scents released by day and at night showed no decrease in scent emission during nighttime, but the odor bouquets were significantly different. Pollinated flowers produced significantly different odor bouquets, and the total amount of scent emitted two to four days after pollination was significantly lower compared with unpollinated flowers. In addition, behavioral tests with A. nigroaenea males showed that flowers were significantly less attractive three days after pollination. This reduced attractiveness is hypothesized to guide pollinators to the unpollinated flowers within an inflorescence, and thus increase the reproductive success of the plant.     

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.     

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.     

Responses of the Pollinating Wasp Ceratosolen solmsi marchali to Odor Variation Between Two Floral Stages of Ficus hispida

During development of figs on Ficus hispida, only the female floral stage is receptive to its pollinator Ceratosolen solmsi marchali. After this stage, the quantity of fig odor decreases. The effects of F. hispida volatiles from receptive figs (figs at the female floral stage, when they are pollinated) and interfloral figs (between the female floral and male floral stages) on their pollinator were studied, together with responses to compounds present in the odor. Odors emitted by both receptive and interfloral figs were attractive to the pollinator. However, wasps preferred the odor of receptive figs to that of interfloral figs even though the quantity of interfloral volatiles increased. Three monoterpenes that included linalool (major constitutent) and two minor compounds limonene and β-pinene from the receptive fig volatiles were used to test the pollinator responses. The levoisomer and racemic mixtures of linalool were attractive to the pollinator at high doses, but the dextroisomer was neutral. (±)-Limonene and (−)-β-pinene at high doses were even less attractive to the pollinator than clean air and were neutral at low doses, while (R)-(+)-, (S)-(−)-limonene were neutral at all doses. In blend tests, all four mixtures of (±)-linalool or (S)-(−)-linalool combined with (±)-limonene or (−)-β-pinene attracted C. solmsi marchali when administered at high doses. (R)-(+)-linalool and (−)-β-pinene enhanced the attractiveness of (S)-(−)-linalool to the pollinator, while enantiomers of limonene did not. These results suggest that both quality and quantity of fig volatiles regulate C. solmsi marchali response and that quality is the main host-finding and floral stage-distinguishing cue for the pollinator. Synergistic effects of some compounds may play a role in enhancing attractiveness of the active compounds.     

Floral Odor Variation in Two Heterostylous Species of <Emphasis Type="Italic">Primula</Emphasis>

Floral traits such as odor, color, and morphology are important pollinator attractants. Variation in floral traits may influence floral constancy, the tendency of pollinating insects to visit flowers of only one type. We investigated for the first time variation in odor between floral morphs in heterostylous species. We analyzed inter- and intraspecific odor variation in the pin and thrum floral morphs of sympatric Primula elatior and P. farinosa (Primulaceae). Floral volatiles were sampled with headspace sorption. Quantitative analysis and chemical identification were performed by gas chromatography coupled to mass spectrometry. The species produced different floral bouquets. P. elatior emitted mostly limonene with small amounts of -pinene, myrcene, and sabinene. P. farinosa produced benzaldehyde, 4-oxoisophorone (2,6,6-trimethyl-2-cyclohexene-1,4-dione), benzyl alcohol, and benzyl acetate. These interspecific differences may play a role in promoting floral constancy and maintaining species integrity. Conversely, no differences were detected between the scents of pin and thrum morphs within each species. Heterostyly relies on pollinators visiting both floral morphs. There may be a stabilizing selection against divergences in traits that may cause pollinators to develop floral constancy to only one of the floral morphs.This revised PDF version was published online in May 2005 with added Published Online dates.     

Urinary signaling pheromone and specific behavioral response in tree shrews (Tupaia belangeri)

As soon as they encounter the scent marks made by the urine of fertile male conspecifics, tree shrews of both sexes cover the scent marks with their own sternal-gland secretion by chinning. The urine of other species, female conspecifics, or castrated male conspecifics does not elicit this behavior; that is, overmarking with sternal-gland secretion is a reaction to a specific chemical signal. The intensity of the overmarking reaction, i.e., the chinning score in response to the urine sample, decreases as the urine is diluted. The urine of different male conspecifics elicits overmarking of varying intensity; an animal's own urine is in general not overmarked. This behavioral reaction meets all the criteria for a bioassay of potential use in isolating the tree-shrew pheromone from urine.     

Interspecific response to sex pheromones,and calling behavior of severalAttagenus species (Coleoptera: Dermestidae)

Females of severalAttagenus species demonstrated calling behaviors similar to those previously reported forA. elongatulus. Attagenus rufipennis females did not call until they were 12–14 days old. OtherAttagenus species called at approx. 4 days of age. All species exhibited diurnal periods of calling activity. Interspecific pheromone responses were tested, withA. megatoma megatoma, A. megatoma canadensis, A. megatoma japonicus, andA. schaefferi spurcus showing equal cross-responses. Male response to females was demonstrated inA. rufipennis andA. bicolor. Attagenus rufipennis, bicolor, andelongatulus males responded only to female extracts of their own species.Mention of a proprietary product does not constitute an endorsement by the USDA.     

Individual, Sexual, Seasonal, and Temporal Variation in the Amount of Sagebrush Lizard Scent Marks

Although many animals deposit scent marks, previous studies have focused almost entirely on rodents or on the chemical structure of the signal. Here, we study the quantity and temporal pattern of chemical deposition by the territorial sagebrush lizard Sceloporus graciosus, measuring both femoral pore and fecal deposits. Specifically, we tested whether variation in deposition is a good cue of individual and sexual identity and/or whether it is more closely associated with body size and reproductive state, indicators of physiological condition. The results support the latter hypothesis. We found that although the amount of fluid deposited on a single perch (rarely quantified in mammals) carries little information on individual or sexual identity, it reflects the physiological condition and reproductive state of individual lizards and is replenished on a roughly weekly cycle, potentially providing additional information on the producer's activity level. The amount of deposition may thus provide important information to chemical receivers making mate choice and territorial defense decisions. The results further suggest that seasonal increases in gland production allow lizards to mark more sites rather than to influence the quality of the signal on a single perch.     

Disease Status and Population Origin Effects on Floral Scent<Emphasis Type="SmallCaps">:</Emphasis> 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.     

Composition of larval secretion ofChrysomela lapponica (Coleoptera,Chrysomelidae) and its dependence on host plant

The defensive secretion ofChrysomela lapponica larvae, which is produced by nine pairs of exocrine dorsal glands, has been chemically analyzed. TheC. lapponica larvae were kept in the laboratory on leaves of either birch (Betula pendula), alder (Alnus glutinosa), or willow (Salix fragilis). Larvae developed normally on birch and willow, whereas those on alder died within a few days. GC-MS analyses of the secretion of larvae on birch and willow revealed that the composition of this secretion differs distinctly from the known ones of several otherChrysomela species feeding exclusively on Salicaceae. In the exocrine secretion of larvae on birch, 69 compounds were identified, which included the main components isobutyric acid, 2-methylbutyric acid, and esters of the two. Several of the esters have not been reported previously from nature. The alcoholic components of the esters may be hydrolysis products ofBetula glycosides. Most components of the secretion of larvae feeding on birch were also found in the secretion of larvae feeding on willow. In addition, major amounts of benzoic acid and salicylalcohol were present in the secretion of the larvae feeding on willow.C. lapponica obviously acquires salicylalcohol by hydrolysis of salicin from willow leaves. However, in contrast to otherChrysomela species,C. lapponica larvae oxidize only traces of salicylalcohol to salicylaldehyde. The repellent activity of single authentic compounds of the secretion of larvae feeding on birch and willow, respectively, was tested in laboratory bioassays with ants (Myrmica sabuleti). Biosynthetic pathways to some identified compounds are suggested and discussed under evolutionary and functional aspects.     

Responses to inter- and intraspecific scent marks in pine martens (Martes martes)

In order to analyze intra and interspecific olfactory discrimination, behavioral responses (sniffing and marking) towards various odors were observed in pine martens (Manes martes). Two adult males and two adult females were tested for intraspecific discrimination of abdominal gland odors and urine. Both sexes sniffed and marked objects carrying their own scent less than unscented objects. There were no differences in sniffing or marking objects impregnated with odors from known and unknown conspecifics of the opposite sex or objects carrying the odor of an unknown male or female. A second experiment with two adult females gave no evidence for interspecific discrimination: no differences emerged when comparing reactions towards marks of pine martens, stone martens (a closely related species), or genets. The most obvious result of this study is the reduced response of pine martens towards their own mark. It is suggested that scent marking in martens may reflect autocommunication, the primary effect being to familiarize an animal with its environment.     

Chemical Profiles of Scent Gland Secretions in the Cyphophthalmid Opilionid Harvestmen, <Emphasis Type="Italic">Siro duricorius</Emphasis> and <Emphasis Type="Italic">S. exilis</Emphasis>

Gas chromatographic–mass spectrometric analyses of the scent gland secretions of Siro duricorius and S. exilis (Opiliones, Cyphophthalmi, Sironidae) revealed a set of 24 components, comprising a series of saturated and unsaturated methyl ketones (C11–C15) and four naphthoquinones. Whereas the scent gland secretions of S. duricorius, collected in Austria, and S. exilis from USA were qualitatively nearly indistinguishable (with the exception of acetophenone that was specific to S. duricorius), they distinctly differed in their relative quantitative compositions: major components of the secretion of S. duricorius were 7-tridecen-2-one, tridecan-2-one, undecan-2-one, 1,4-naphthoquinone, 6-methyl-1,4-naphthoquinone (tentatively identified only), and 4-chloro-1,2-naphthoquinone. In contrast, in S. exilis a compound tentatively identified as 6-methyl-4-chloro-1,2-naphthoquinone was present in large amounts (in S. duricorius a trace component), whereas undecan-2-one only occurred in minor quantities. Secretion profiles of juveniles and adults (both sexes) of each species showed high correspondence.This is the first report on the chemistry of scent gland secretions of the opilionid suborder Cyphophthalmi. 4-Chloro-1,2-naphthoquinone was identified as a new exocrine product of arthropods, whereas 1,4-naphthoquinone and the tentatively identified 6-methyl-1,4-naphthoquinone are known constituents of exocrine secretions from one species of palpatorid opilionids, Phalangium opilio. In contrast, all ketones identified were new for opilionid scent glands, although similar ketones are characteristic of scent gland secretions of palpatorid genera Leiobunum and Hadrobunus. With regard to the near-basic position of Cyphophthalmi in currently proposed phylogenetic trees of Opiliones, naphthoquinones and ketones from Siro may represent the condition ancestral to the (derived) naphthoquinone- and ketone-rich secretions in phalangid Palpatores.     

Patterns of scent-mounding in a population of beaver (Castor canadensis)

The frequency and pattern of distribution of scent-mound construction were studied in a population of beaver in southeast Ohio from 1975 through 1977. The study addressed the questions of whether or not the frequency of scent-mound construction varied with season, site, year, and degree of contact with other family groups, and whether the pattern of scent-mounding activity was parsimonious with the idea of territorial marking. The number of scent-mounds constructed was determined weekly for each site throughout the ice-free season. Scent-mounding activity was highest in spring and declined and remained low during summer and fall. Significant differences were found amoung sites and over years. Contact with other resident family groups altered both frequency and pattern of scent-mound construction. Scent-mounds did not conform to a scent-fence model. The most parsimonious interpretation of function of odor cues deposited on scent-mounds is the effect on the motivational state of residents and nonresidents, increasing the confidence and reducing anxiety in residents smelling their own scent-mound and decreasing the confidence and increasing the readiness to flee in trespassers encountering a strange scent-mound.     

Bacterial contents of the anal and castor glands of beaver (Castor canadensis)

Bacterial contents of both the anal gland and castor gland of the beaver (Castor canadensis) were determined. Using our culture methods, no bacteria were isolated from the castor glands, but the anal gland contained high numbers of the aerobeEscherichia coli and the anaerobeBacteroides fragilis. The latter may be represented by several variants but facilities were not available for advanced anaerobic analysis. The relative numbers of each bacterial group and the group present were constant regardless of sex, age class, or colony of beaver. The bacterial fermentation hypothesis is rejected for castor gland section but remains possible for anal gland secretions based on variations seen inB. fragilis. The role of the products of both the castor gland and anal gland are discussed in relationship to scent communication in beaver.     

Variation of Piperidine Alkaloids in Ponderosa (Pinus poderosa) and Lodgepole Pine (P. contorta) Foliage from Central Oregon

We quantified 2,6-disubstituted piperidine alkaloids in Pinus ponderosa and P. contorta needles from three forest sites in April, June, August, and December. Alkaloids were detected on at least one date in 71% of the ponderosa pine and in 29% of the lodgepole pine trees sampled. Pinidine was the major alkaloid constituent of ponderosa pine, while euphococcinine was the predominant compound in lodgepole pine. For ponderosa pine, total alkaloid concentrations were very low at two sites on all dates. At the third site, concentrations were variable but significantly higher on all dates. Total alkaloid concentrations in previous-year foliage from this site were highest in April, then significantly lower from June through December. Current-year foliage collected in August and December had significantly higher alkaloid concentrations than previous-year foliage on the same dates. Variation in foliar nitrogen concentrations accounted for some of the alkaloid variation in current-year foliage sampled in August.     

Comparative analysis of steam distilled floral oils of cacao cultivars (Theobroma cacao L., Sterculiaceae) and attraction of flying insects: Implications for aTheobroma pollination syndrome

Steam-distilled floral fragrance oils from nine distinctive cultivars ofTheobroma cacao L. (Sterculiaceae) in Costa Rica were examined with GC-MS to determine whether or not major differences existed among these cultivars for volatile constituents comprising 50% or more of the samples. The cultivars selected for floral oil analyses were chosen to represent diverse cultivars having supposedly different genetic backgrounds and histories of artificial selection for agronomic purposes. Cluster analysis revealed two major groupings of cultivars: those with higher molecular weight dominant compounds, and those having lower molecular weight compounds. Additionally, one cultivar, Rim-100, selected from criollo or ancestral-type cacao in Mexico and resembling criollo in the appearance of flowers and fruits, formed an extreme group having the highest molecular weight profile for major volatile compounds. Based upon these analyses, bioassays using McPhail traps were performed in an abandoned cacao plantation in northeastern Costa Rica during rainy and dry seasons to determine the relative attraction of these oils to flying insects. Bioassays revealed that the Rim-100 cultivar attracted by far the greatest numbers of cacao-associated midges (Diptera: Ceratopogonidae and Cecidomyiidae), as well as stingless bees (Hymenoptera: Apidae: Meliponinae), suggesting that a floral fragrance having high-molecular-weight volatiles is more potent as an attractant to flying insects than floral oils having lower-molecular-weight compounds. It is suggested that Rim-100 more closely resembles an ancestral or wild-type cacao than the other cultivars examined, and therefore it is more effective in attracting opportunistic dipteran floral visitors and pollinators than other cultivars in plantation settings. Several of the major volatile compounds found in the floral oils ofT. cacao and other species ofTheobroma occur in mandibular and other exocrine glands in various bees, including stingless bees and halictids, known visitors ofTheobroma flowers. These compounds are particularly present in noncultivated species ofTheobroma and have much more noticeable fragrances than the seemingly scentless flowers of cultivatedT. cacao selected for agriculture. It is hypothesized that the floral attraction system of ancestral or wild (noncultivated)T. cacao and other species ofTheobroma may have evolved to attract certain bees as their principal pollinators in natural habitats in the Neotropics, with a floral reward hypothesized as being sociochemicals needed by bees for mating, foraging, territorial defense, etc. Because of the many generations of extensive selection by cloning for desired cultivars,T. cacao might have lost much of its original floral attraction system for bees, instead being pollinated opportunistically by dipterans in plantation habitats. This may help to explain why natural pollination in cultivatedT. cacao is generally very poor relative to observed levels of fruit-set in wild or noncultivated species ofTheobroma.     

The social role of scent marking in beaver (Castor Canadensis)

Beaver colonies with close neighbors constructed more scent mounds than did isolated colonies, and the number of scent mounds at each active lodge is correlated with the distance to the nearest occupied lodge. The scent mounds were typically located at trails, also on lodges and dams. The beaver rebuilt experimentally removed scent mounds. Experimentally scent-marked unoccupied lodges were less often visited or inhabited than unscented control lodges. Resident beaver responded to artificial scent marks near their lodges with aggressive behavior and increased activity. We conclude that scent mounds serve in delineating family territories and are effective in deterring transient beaver from utilizing existing but uninhabited lodges.     

Seed chemistry of Sophora chrysophylla (mamane) in relation to diet of specialist avian seed predator Loxioides bailleui (palila) in Hawaii

This study describes the chemical ecology of a tritrophic interaction among species endemic to the island of Hawaii, USA: a tree (Sophora chrysophylla: mamane), an endangered bird (Loxioides bailleui; palila), and moth larvae (Cydia spp.). Palila and Cydia both specialize on the seed embryos of mamane but avoid eating the seed coats. Palila actively seek out and feed mamane embryos and Cydia larvae to their nestlings. Because mamane embryos contain potentially toxic levels of alkaloids, including broadly toxic quinolizidine alkaloids, and because insects often sequester alkaloids from their food plants, we focus on the questions of why palila forage upon mamane embryos and why they supplement their diet with Cydia larvae. Our data show that mamane embryos contain high amounts of potentially toxic alkaloids, but are well balanced nutritionally and contain lipids, carbohydrates, proteins, amino acids, and minerals at levels that are likely to be sufficient for maintenance and breeding. Mamane seed coats contain lower levels of alkaloids and nutrients, somewhat higher levels of phenolics, and much higher levels of nondigestible fiber. Taken together, these results suggest that palila have evolved tolerance to high levels of alkaloids and that they forage upon embryos primarily because of their availability in the habitat and high nutritional reward. Our data also suggest that Cydia are used by palila because they are readily accessible, nontoxic, and nutritious; the larvae apparently do not sequester alkaloids while feeding upon mamane seeds. Our results are interpreted with respect to the likelihood of current and historical coadaptive responses in this ecologically isolated and simplified island setting.