Flower scent composition in Dianthus and Saponaria species (Caryophyllaceae) and its relevance for pollination biology and taxonomy

Floral fragrance compounds of seven Dianthus species (D. arenarius, D. armeria, D. barbatus, D. deltoides, D. monspessulanus, D. superbus, and D. sylvestris) and one Saponaria species (S. officinalis) (Caryophyllaceae) were studied using headspace adsorption technique followed by gas chromatography massspectrometry (GC-MS). The number of compounds (fatty acid derivatives, benzenoids, phenyl propanoids, isoprenoids, and nitrogen containing compounds) identified in the floral odors ranged from 18 to 51 but all were dominated by only 1–3 compounds. Most of the compounds identified in this study have been previously reported in floral scents from species of the closely related genus Silene L. However, the phenyl propanoids eugenol, methyleugenol, methylisoeugenol, cis-asarone, and trans-asarone have formerly not been found in Silene. Based on the measurement of Sørensen’s index of similarity (I_s) nonmetric multidimensional scaling (MDS) was used to detect meaningful underlying dimensions and to visualize similarities between the investigated species. The MDS analysis showed three groups of species, (1) the diurnal D. armeria, D. barbatus, and D. deltoides are characterized by the predominance of fatty acid derivatives, (2) the closely related nocturnal D. monspessulanus, and D. superbus by high relative amounts of isoprenoids such as cis-β-ocimene and β-caryophyllene, and (3) the species D. arenarius, D. sylvestris and S. officinalis by a predominance of benzenoids, especially methylbenzoate. The results are discussed in relation to pollination, especially by butterflies, moths, and hawkmoths.     

Temporal variation of flower scent in Silene otites (Caryophyllaceae): a species with a mixed pollination system

Floral scent composition and emission are often related to olfactory abilities, preferences and activity times of pollinating agents. However, most studies have focused on species with one pollinator type, and little is known about species with mixed pollination systems. We investigated the temporal variation in flower visitor activity and flower scent emission of Silene otites (Caryophyllaceae), a species regarded as being nocturnal and pollinated by moths and mosquitoes. We found, however, that S. otites is not only visited at night by moths and mosquitoes, but also by a wide range of day‐active insects. Furthermore, both the intensity and composition of floral scent change during the course of the day. Total scent emission reached its maximum in the early hours of the night when compounds known to be attractants for moths and/or mosquitoes, such as lilac aldehyde, benzaldehyde, phenylacetaldehyde and 2‐phenylethanol, dominated the scent. However, although less intensive, emission continued during the day. In the early morning, α‐pinene, hotrienol, 2‐phenylethanol and δ‐3‐carene were the dominant scent compounds. (E)‐β‐Ocimene, hotrienol and benzyl alcohol contributed proportions of at least 10% before midday when flies, such as syrphids, were abundant flower visitors, whereas linalool and hotrienol contributed to the scent with at least 10% each in the afternoon when bees also contributed to flower visits. We conclude that, in S. otites, the changing emission patterns are ‘in tune’ with the olfactory abilities, preferences and activity times of its day‐ and night‐active potentially pollinating flower visitors. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 169 , 447–460.     

Silene oenotriae (Caryophyllaceae): a new species from S Italy

Silene oenotriae a new species of S. sect. Siphonomorpha is described and illustrated. It is a rare chasmophyte growing on limestones along the gorges of southern slope of Mt. Pollino (S Italy). Its relationships are discussed.     

Silene ichnusae (Caryophyllaceae), a new species from Sardinia

Silene ichnusae (Caryophyllaceae) a new species of S. sect. Siphonomoipha is described and illustrated. It is a rare chasmophyte localized at Capo Falcone (W Sardinia), on siliceous rocks near the sea. Its relationships with S. velutina, of the S. mollissima group, are discussed.     

A new species of Silene (Caryophyllaceae) from east Anatolia, Turkey

Silene bitlisensis O.Tugay & Ertugrul from the Green Line Afforestation Zone (B9: Bitlis Province) is a new species described and illustrated here. It is closely related to S. caramanica Boiss. & Heldr. var. ilarslanii Aytaç & Dural, from which it mainly differs in its habit, leaf, and floral features.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 463–466.     

A new species of Silene (Caryophyllaceae) from South Anatolia, Turkey

Silene doganii A.Duran & Y.Menemen sp. nov. from the Amanos Mountains (C6: Osmaniye-Turkey) is described and illustrated. It is closely related to S. caramanica Boiss. & Heldr., from which it differs mainly in its habit, hairiness, leaf and floral features.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 109−113.     

Gender lability in trioecious Silene acaulis (Caryophyllaceae)

Gender expression of individual cushions of Silene acaulis was shown to vary between years. Fifteen of thirtnine (= 38%) cushions monitored changed gender expression between 1993 and 1995. Cushions dominated by female flowers were shown to be more stable in gender expression than cushions dominated by male or hermaphrodite flowers.     

Flower herbivory and seed predation in Silene vulgaris (Caryophyllaceae): effects of pollination and phenology

Pollination and seed predation were studied in Silene vulgaris populations during two seasons, one with much lower pollinator abundance than the other. Among the pollinators, noctuid moths of the genus Hadena also acted as seed predators. Nectar-foraging female moths oviposited in flowers, and their larvae consumed flowers and seed capsules.
Despite a lower percentage of pollinated flowers in the year of low pollinator abundance, similar numbers of flowers set fruit in both years, because fewer flower buds and flowers were eaten by Hadena larvae during the year of low pollinator visitation. The number of seed capsules preyed upon was also lower in the year with low pollinator abundance, resulting in a higher seed set. The positive correlation between the percentage of pollinated flowers and the percentage of seed capsules destroyed was also observed when comparing flowers opening in different parts of the season.
Early flowering plant individuals had the same pollination success but suffered higher seed predation than late flowering ones. Selection for maximized pollination success through synchronous flowering, is probably the main reason for the compressed flowering period in 5. vulgaris , but the high level of predation early in the season may further increase the reproductive success of synchronous flowering individuals.     

A new species and a new combination in western North American Silene (Caryophyllaceae)

Silene nachlingerae is described, illustrated, and compared toS. aperta. The similarly floweredS. invisa is considered to be closely related toS. bernardina, and especially to its var.rigidula (Robinson) Tiehm, comb nov.     

Local genetic population structure in an endangered plant species, Silene tatarica (Caryophyllaceae)

Genetic substructuring in plant populations may evolve as a consequence of sampling events that occur when the population is founded or regenerated, or if gene dispersal by pollen and seeds is restricted within a population. Silene tatarica is an endangered, perennial plant species growing along periodically disturbed riverbanks in northern Finland. We investigated the mechanism behind the microspatial genetic structure of S. tatarica in four subpopulations using amplified fragment length polymorphism markers. Spatial autocorrelation revealed clear spatial genetic structure in each subpopulation, even though the pattern diminished in older subpopulations. Parentage analysis in an isolated island subpopulation indicated a very low level of selfing and avoidance of breeding between close relatives. The mean estimated pollen dispersal distance (24.10 m; SD = 10.5) was significantly longer and the mean seed dispersal distance (9.07 m; SD = 9.23) was considerably shorter than the mean distance between the individuals (19.20 m; SD = 13.80). The estimated indirect and direct estimates of neighbourhood sizes in this subpopulation were very similar, 32.1 and 37.6, respectively. Our results suggested that the local spatial genetic structure in S. tatarica was attributed merely to the isolation-by-distance process rather than founder effect, and despite free pollen movement across population, restricted seed dispersal maintains local genetic structure in this species.     

The origin and number of introductions of the Hawaiian endemic Silene species (Caryophyllaceae)

The Hawaiian endemic Silene are a small group of woody or semiwoody representatives from a large, predominantly herbaceous, species-rich genus. We here investigated the origin and number of introductions of the endemic Hawaiian Silene based on phylogenetic relationships inferred from DNA sequences from both the plastid (the rps16 intron) and the nuclear (ribosomal internal transcribed sequences, ITS, and intron 23 of the RPB2 gene) genomes. Silene antirrhina, a widespread weedy American annual, is strongly supported as sister to a monophyletic group consisting of the Hawaiian Silene, indicating a single colonization event. There are no obvious morphological similarities between S. antirrhina and any of the species of Hawaiian Silene. Our results suggest an American origin for the Hawaiian endemics because that would require only a single trans-ocean dispersal. Two of the Hawaiian endemics (S. struthioloides and S. hawaiiensis) that form a subclade in the analyses have evolved woodiness after introduction to the Hawaiian Islands. Our results contribute to other recent results based on molecular phylogenetics that emphasize the American continent as a source area for the Hawaiian flora and support a striking morphological radiation and evolution of woodiness from a single introduction to the archipelago.     

Spectrophotometric analysis of nectar production in Silene vulgaris (Caryophyllaceae)

Significant differences in nectar content were observed between hermaphrodite and female plants of the gynomonoecious-gynodioecious taxon, Silene vulgaris, from populations in northern lower Michigan. These differences in nectar sugar content were observable with a carbohydrate digestion technique involving sulfuric acid, phenol, and measurement of the color change with a spectrophotometer. A hand-held refractometer did not provide sufficient resolution to discern differences between the genders. Both genders were similar in the pattern of sugar content of nectar during floral development. A splitplot factorial design revealed significant differences both among individual plants and stages of floral phenology within each gender. The spectrophotometric technique and statistical analysis provided the needed resolution to discern differences between the genders that we relate to pollinator activity, levels of inbreeding depression, and the maintenance of gynodioecy in this taxon.     

Unstable B chromosomes in Silene maritima With. (Caryophyllaceae)

Unstable B chromosomes in Silene maritima With. (Carophyllaceae). B chromosomes have been found in 7 out of 39 populations of Silene maritima With. (Carophyllaceae) studied. These 7 populations are all from the Norfolk coast. The B chromosome is small, 0.8 μm long, telocentric and appears euchromatic. Within plants the B chromosome is highly unstable with different numbers in cells of the same root or pollen mother cells (pmcs) of an anther. The transmission of the Bs is efficient and in controlled crosses progeny plants usually have higher mean B frequencies than the B-containing parents. At metaphase I the pairing behaviour of the Bs is variable and they often appear as univalents. In general the presence of Bs in pmcs results in an increase in chiasma frequency/cell and populations with Bs have higher mean chiasma frequencies than those without Bs. Cloned plants grown under stress conditions induced by the addition of NaCl to a nutrient solution showed no difference in mean B number/cell or distribution when compared with controls grown in nutrient solution only.     

Nectar reward and advertisement in hummingbird-pollinated Silene virginica (Caryophyllaceae)

We tested for an association between nectar and various floral traits and investigated their roles as primary and secondary pollinator attractants in hummingbird-pollinated Silene virginica. Our goal was to gain insight into the mechanisms of pollinator-mediated selection that underlies floral trait divergence within the genus. In a field population of S. virginica, we measured five floral and eight vegetative traits and quantified nectar volume, nectar sugar concentration, and total sugar reward (nectar volume × nectar sugar concentration). All three components of nectar reward were positively correlated to flower size, and nectar volume varied significantly among individuals within the population. To ascertain whether the correlation of specific floral traits with nectar reward influences the behavior of the primary pollinator of S. virginica, the ruby-throated hummingbird, Archilochus colubris, we investigated whether A. colubris preferred the expression of floral traits associated with high nectar volume and total sugar reward. We accomplished this by constructing floral arrays consisting of artificial flowers that had equal nectar quantity and total sugar reward but that differed in petal area and corolla tube diameter, which were positively correlated with nectar quantity and total sugar reward in our field study. In observations of visitation frequencies to the various floral-trait combinations, hummingbirds preferentially visited artificial floral phenotypes with larger petal displays, with the greatest preference for floral phenotypes with both larger petals and wider corolla-tube diameters. This association between primary and secondary floral attractants and hummingbird discrimination of floral features supports the concept that the floral traits of S. virginica reflect pollinator-mediated selection by the principal pollinator.     

Breeding system in the dichogamous hermaphrodite Silene acutifolia (Caryophyllaceae)

The breeding system of the dichogamous hermaphrodite species Silene acutifolia, endemic to north-west Spain and north and central Portugal, is examined. Pollen germinability and style-stigma receptivity were analysed to determine whether protandry is a barrier to self-fertilization. By 48 h after anthesis, pollen germinability had declined to approx. 10 %. The short straight styles are not receptive when flowers first open. They gradually elongate and curve outwards, develop stigma papillae and become receptive. There is no clear separation between stigma and style: the stigma papillae appear in a line along the length of the style. Fruit set is high regardless of pollen source; however, seed set is significantly reduced after both spontaneous and facilitated autogamy. Seed set following spontaneous autogamy was 30 % (86 % in controls) in 1998 and 33 % (87 % in controls) in 1999. Seed set following facilitated autogamy was 62 % (86 % in controls) in 1998 and 67 % (89 % in controls) in 1999. Thus, separation of the male and female phases does not prevent production of seeds by self-pollination, although it does reduce the likelihood of this. Furthermore, results of the present experiments indicate that this species has no self-incompatibility mechanisms (self-compatibility index = 0.98). The selfing rate in the study population was 0.41, which is supported by the lack of self-incompatibility systems and by the incomplete protandry.     

Diurnal and nocturnal pollination of Silene alba (Caryophyllaceae)

Flowers that are open for >12 h may be visited by both diurnal and nocturnal pollinators. I compared the effectiveness (measured as seed production and pollen movement distance) of diurnal and nocturnal pollinators of Silene alba, a species whose flowers open in evening but close by midmorning the following day. By bagging flowers either during evening hours or during daylight hours or both day and night, I compared seed production caused by diurnal and nocturnal pollinators. Flowers exposed only to nocturnal visitors (mostly sphingid and noctuid moths) produced significantly more seeds than flowers exposed only to diurnal visitors (bees, flies, and wasps). Fluorescent dye applied to anthers moved significantly further and to more stigmas at night than during the day. In both measures of pollination effectiveness, nocturnal-visiting moths are better pollinators of S. alba than are the diurnal-visiting bees, flies, and wasps. These data support the hypothesis that floral phenology is an adaptation to expose flowers to the most effective pollinators.     

Gender polymorphism in flowers of Silene vulgaris (Moench) Garcke (Caryophyllaceae)

Silene vulgaris occurs in Israel as a stolonifcrous tetraploid which forms mostly sexually polymorphic populations. Fully hermaphrodite and fully male-sterile plants are linked by a range of intermediate forms which are gynomonoecious and bear hermaphrodite, male-sterile, and partially male-sterile flowers. Male-sterile flowers differ from hermaphrodite ones by having a narrower calyx, a shorter corolla, a thicker style, and a considerably larger stigmatic area with longer papillae which are more markedly bulbous basally. In individual anthers of hermaphrodite flowers, diameters of stained pollen grains showed a continuous variation from 36 to 80 μm with a modal value of 56. About 30% of pollen was found to be non-stainable. Reduction in male fertility occurs at different levels, from small or inviable pollen grains through abortion of single anthers, abortion of entire androecia, and through different degrees of gynomonoecy to totally male-sterile individuals. The proportion of stainable pollen to ovules in hermaphrodite flowers alone was found to be less than 100. From the data presented, less than a third of all ovules produced in the different kinds of flower develop into seeds. This may reflect an inadequacy of pollen, which the local population of S. vulgaris can tolerate because of its stoloniferous habit.     

Genetic differentiation in endemic Silene (Caryophyllaceae) on the Hawaiian Islands

Endemic Hawaiian Silene colonize new lava flows and are outcompeted as the ground ages. They illustrate the genetic processes operating in the evolution of pioneering island plants. The volcanic history of the Hawaiian Islands allows an estimation of the age of these plant populations. In this study, populations of S. struthioloides from Maui and the older part of the island of Hawaii, and S. hawaiiensis from the youngest volcanoes of the island of Hawaii were analyzed by enzyme electrophoresis. The genetic structures of these populations were placed in a geographic and geologic context. Silene is much more polymorphic on the older island, Maui. Genetic variation appears to have been lost in the colonization of the youngest island, Hawaii. Interestingly, some loci for populations on the younger volcanoes of the island of Hawaii are monomorphic for alleles not found in populations on the older part of Hawaii. Recurrent colonizations are accompanied with founder effects, and restricted gene flow among populations has led to isolation and genetic drift. This has resulted in genetic and morphological differentiâtion of Silene populations on the youngest volcanoes.