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.     

Flower scent composition in night-flowering Silene species (Caryophyllaceae)

Floral scent of 13 night-flowering Silene species (Caryophyllaceae) was collected by headspace adsorption and analysed via gas chromatography and mass spectrometry. Benzenoids together with isoprenoids dominated the scent in all species. Among the benzenoids, benzaldehyde (Silene subconica 35.5%, Silene succulenta 23.1%, Silene sericea 15.6%, Silene vulgaris 12.2%, and Silene nutans 9.9%), methylbenzoate (Silene saxifraga 96.1%, S. succulenta 15.2%), benzyl acetate (Silene dichotoma 37.8%, S. nutans 30.1%, Silene italica 9.0%, and Silene latifolia 5.5%), or benzyl alcohol (Silene viscosa 36.1%) occur in the largest amounts. p-Cresol is only found in the floral scent of S. dichotoma (28.5%). Among the isoprenoids, monoterpenes occur in the largest amounts (myrcene 23% in Silene chlorantha, trans-β-ocimene 27.2% in S. nutans and 34.9% in S. sericea, fenchyl acetate 12.7% in S. chlorantha, β-linalool 40.5% in S. chlorantha and 14.5% in S. italica). Relatively high amounts of lilac compounds occur in S. latifolia (49.1%), Silene otites (35.7%), S. subconica (15.2%), and S. vulgaris (59.6%). Higher amounts of sesquiterpenes (isoprenoids) were only found in Silene vallesia with β-bourbonene and γ-muurolene.The vast majority of chemicals identified are common components of a wide array of scented angiosperm flowers. Nevertheless, the results conform most strongly with the findings in other night-blooming and/or moth-pollinated flowers. All investigated Silene species follow the general trend of floral scent compounds typical for moth-pollinated flowers, i.e. flowers having acyclic terpene alcohols (e.g. linalool), aromatic alcohols (benzyl alcohol, 2-phenylethanol) and esters derived from them, and small amounts of nitrogen-containing compounds.     

Characterization of microsatellite loci in the Hawaiian endemic shrub Schiedea adamantis (Caryophyllaceae) and amplification in related species and genera

Schiedea adamantis is a rare, perennial shrub endemic to the Hawaiian island of Oahu where it consists of a single population. Using a nonradioactive protocol, 12 microsatellite primers were developed that consisted of di-, tri-, penta- and hexanucleotide repeats. Using multiplexed reactions, all but two primers exhibited polymorphism with an average of 3.67 alleles per primer. Most primers also amplified in 28 additional Schiedea species, revealing wide applicability across the genus; eight and nine primers also amplified in Honckenya peploides and Silene lanceolata, respectively, related genera in the Caryophyllaceae. This is the first known report of microsatellite primers developed in Schiedea.     

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.     

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.     

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 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.     

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.     

Enzyme polymorphism, morphometric variation and population structure in a restricted endemic, Silene diclinis (Caryophyllaceae)

Silene diclinis is a dioecious perennial herb, restricted to a small area of the SE Spanish province of Valencia. Polyacrylamide gel electrophoresis and morphometric analysis were carried out on cultivated material derived from seed collected from the main population of S. diclinis at Játiva. Only two out of 26 inferred enzyme loci showed substantial variation. There was some indication of population subdivision in both. The esterase locus also showed homozygote excess within the population as a whole and within one subpopulation. Morphological characters showed significant differentiation between subpopulations.
Low allozyme variability characterizes populations of most endemic species that have been investigated. Isolation and historical events may have been as important as population size or edaphic specialization in causing this low variability. But S. diclinis resembles other outbreeding plants in showing population structure and homozygote excess, suggesting restricted within-population gene flow. Mechanisms that may restrict gene flow in S. diclinis include environmentally-induced differences in flowering time, poor seed dispersal and possibly short pollinator foraging distances. Morphological variability and the incidence of developmental abnormalities are speculatively linked with homozygosity. Storage of genetic diversity in space can occur in restricted as well as widespread species and sampling for gene banking should then be spatially representative. Silene diclinis is threatened by continued habitat loss and consequent genetic erosion; its long-term future may depend on the gene bank and the botanic garden.     

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.     

Demographic change and microhabitat variability in a grassland endemic, Silene douglasii var. oraria (Caryophyllaceae)

Variable spatial and temporal environments are known to affect the population dynamics of plants, but studies of local scale variability and its relationship to demographic change within a population remain limited. Using mapped plants, we examined the population dynamics of a coastal grassland endemic, Silene douglasii var. oraria, in two habitats over 10 yr. We hypothesized that ecological differences between rocky and grassy habitats might influence demographic parameters, including adult survival, growth, and density. Soil pH, soil moisture. and other abiotic variables differed little between habitats, but microsite differences in light, soil depth. and vegetation height were related to variation in Silene density and plant circumference. We also found significantly higher population densities, lower adult mortality, and more juvenile recruitment in rocky areas. Finite rates of population growth varied across years and habitats (lambda = 0.82-1.12). with different patterns evident in the two habitats. In both, observed population sizes in 1992 were similar to matrix projections using 1982-1985 data. Populations declined in size in some years despite high adult survivorship and variable recruitment. More intensive study of seedlings is needed, including experimental evaluation of the role of light and competition. However, the habitat-specific differences we observed imply that ecological studies and conservation plans developed for rare plants should consider the effect of local scale variability on demography.     

Origin and evolution of North American polyploid Silene (Caryophyllaceae)

Nuclear DNA sequences from introns of the low-copy nuclear gene family encoding the second largest subunit of RNA polymerases and the ribosomal internal transcribed spacer (ITS) regions, combined with the psbE-petL spacer and the rps16 intron from the chloroplast genome were used to infer origins and phylogenetic relationships of North American polyploid Silene species and their closest relatives. Although the vast majority of North American Silene species are polyploid, which contrasts to the diploid condition dominating in other parts of the world, the phylogenetic analyses rejected a single origin of the North American polyploids. One lineage consists of tetraploid Silene menziesii and its diploid allies. A second lineage, Physolychnis s.l., consists of Arctic, European, Asian, and South American taxa in addition to the majority of the North American polyploids. The hexaploid S. hookeri is derived from an allopolyploidization between these two lineages. The tetraploid S. nivea does not belong to any of these lineages, but is closely related to the European diploid S. baccifera. The poor resolution within Physolychnis s.l. may be attributed to rapid radiation, recombination among homoeologues, homoplasy, or any combination of these factors. No extant diploid donors could be identified in Physolychnis s.l.     

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.     

Molecular phylogeny and adaptive radiation of the endemic Hawaiian Plantago species (Plantaginaceae)

Insular oceanic islands provide excellent opportunities for the study of evolutionary processes and adaptive radiation. The Hawaiian Plantago radiation comprises six endemic taxa showing considerable inter- and intraspecific morphological and ecological diversity. The rDNA internal (ITS) and external (ETS) transcribed spacers and two recently described chloroplast spacers, ndhF-rpl32 and rpl32-trnL, were sequenced to study phylogenetic relationships within this morphologically complex group. Phylogenetic analysis provided strong evidence for the monophyly of Hawaiian Plantago, suggesting that the lineage arose from a single long-distance dispersal event. Inconsistencies between nuclear and chloroplast phylogenies suggest a history of hybridization. The basal, unresolved dichotomy of the combined phylogeny is consistent with rapid phenotypic diversification of the major lineages early in the history of this group. Speciation has largely occurred allopatrically, with divergence a result of intraisland ecological shifts between bog and woodland habitats and interisland dispersal events. Most interisland colonizations were from older to younger islands with initial colonization of Kaua'i. In our analysis, P. pachyphylla is paraphyletic and taxonomic separation of the distinct morphotypes of this species appears justified. Furthermore, the apparent hybrid ancestry and unique morphology and habitat of the endangered P. princeps var. longibracteata support its recognition at the specific rank.     

Allozyme and chloroplast DNA variation in island and mainland populations of the rare Spanish endemic, Silene hifacensis (Caryophyllaceae)

Silene hifacensis is a narrowly endemicplant, restricted to a few small populations onlimestone cliffs in the Spanish province ofAlicante and on the Balearic island of Ibiza.The species was collected to extinction in itsoriginal mainland location by the early 20thcentury. Attempts have been made to reintroduceS. hifacensis to this area butconservation efforts are limited by a lack ofinformation on the geographic structure ofgenetic variation in the species. We usednuclear (allozyme) and chloroplast DNA (cpDNA)PCR/RFLP markers to investigate the structureof genetic variation in 2 mainland and 6 Ibizanpopulations. Levels of allozyme variation werelow, with a mean of 2 alleles per polymorphiclocus. Mean (over polymorphic loci) totalallozyme diversity (H_tot) was 0.203 and meanwithin-population diversity (H_pop) was 0.085. Mostdiversity was explained by thebetween-population diversity component (G_pop.reg =57%). Both mainland populations showedallozyme fixation. Three composite cpDNAhaplotypes were identified. The first is uniqueto a mainland population that is alsoallozymically distinct from all the otherpopulations. The second haplotype is found inthe other mainland population and one Ibizanpopulation: these two populations areallozymically identical. The remaining Ibizanpopulations contain the third haplotype. Thegeographic distribution of allozymes and cpDNAhaplotypes is discussed in terms of populationhistory, dispersal and, speculatively, in termsof the possibility that there has beenundocumented translocation of material betweenpopulations.     

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.