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.     

Life history of the long-lived gynodioecious cushion plant Silene acaulis (Caryophyllaceae), inferred from size-based population projection matrices

Alpine plants often appear to have long life-spans as an adaptation to harsh and unpredictable environmental conditions, yet many lack reliable indicators of age that would make it possible to determine their true longevity. Their extended life-spans also pose problems for measuring lifetime reproductive success, a key component of breeding system evolution in species such as the gynodioecious cushion plant Silene acaulis. For a population of S. acaulis in south-central Alaska, we applied a recently derived analytical approach using size-based population projection matrices that allowed us to estimate: (1) the relationship between cushion diameter and age; and (2) lifetime reproductive success through seed production by females relative to hermaphrodites. Because of a combination of slow growth, frequent shrinkage, and extremely high adult survival, we estimate that the largest cushions in our study population exceed 300 yr in age, and some may live substantially longer, despite the seemingly inhospitable alpine environment they inhabit. Females are estimated to produce 4.4 times as many offspring via seed production over the course of their lives as do hermaphrodites, a difference that is more than sufficient to assure the persistence of females despite their inability to transmit genes through pollen. These results highlight the utility of size-based projection matrices for studying the life histories of herbaceous perennials whose life-span and lifetime reproductive success cannot be determined easily by any other means.     

Pollination ecology of Silene acutifolia (Caryophyllaceae): floral traits variation and pollinator attraction

BACKGROUND AND AIMS: The floral display influences the composition of pollinators interacting with a plant species. Geographic and temporal variation in pollinator composition complicates the understanding of the evolutionary consequences of floral display variation. This paper analyses the relationships between Silene acutifolia, a hermaphroditic perennial herb, and its pollinators, based on field studies in the north-west of Spain. METHODS: Studies were conducted over three years (1997-1999). Firstly, the main pollinators of this species were determined for two years in one population. Secondly, pollen limitation in fruit and seed production was analysed by supplementary hand pollinations, and counting the pollen grains and tubes growing in styles for two different-sized populations. Finally, the effect of flower size and number on the rate of visitation and total seed number was examined for 15 marked plants. RESULTS AND CONCLUSIONS: The primary pollinators were long-tongued insects, including Hymenoptera, Lepidoptera and Diptera, but the composition and visitation frequencies differed between years. Pollen limitation occurred in one of the years of study. There was between-population variation in the number of pollen grains and pollen tubes found in styles, suggesting pollen limitation in one population. Overall, pollinators visited plants with more open flowers more frequently, and pollinated more flowers within these plants. Conversely, petal and calyx sizes had no effect on insect visitation. Plants with higher rates of visits produced higher number of seeds, suggesting that pollinator-mediated limitation of seed and fruit production may be important in some years.     

Variation in the intensity of inbreeding depression among successive life-cycle stages and generations in gynodioecious Silene vulgaris (Caryophyllaceae)

Inbreeding depression is one of the hypotheses explaining the maintenance of females within gynodioecious plant populations. However, the measurement of fitness components in selfed and outcrossed progeny depends on life-cycle stage and the history of inbreeding. Comparative data indicate that strong inbreeding depression is more likely to occur at later life-cycle stages. We used hermaphrodite individuals of Silene vulgaris originating from three populations located in different valleys in the Swiss Alps to investigate the effect of two generations of self- and cross-fertilization on fitness components among successive stages of the life cycle in a glasshouse experiment. We detected significant inbreeding depression for most life-cycle stages including: the number of viable and aborted seeds per fruit, probability of germination, above ground biomass, probability of flowering, number of flowers per plant, flower size and pollen viability. Overall, the intensity of inbreeding depression increased among successive stages of the life cycle and cumulative inbreeding depression was significantly stronger in the first generation (delta approximately 0.5) compared with the second generation (delta approximately 0.35). We found no evidence for synergistic epistasis in our experiment. Our finding of more intense inbreeding depression during later stages of the life cycle may help to explain the maintenance of females in gynodioecious populations of S. vulgaris because purging of genetic load is less likely to occur.     

Silene rothmaleri P. Silva (Caryophyllaceae), a rare, fragmented but genetically diverse species

Silene rothmaleri is an endemic Portuguese species considered extinct until 1992, when it was rediscovered in the wild with a highly fragmented distribution. These rare plants occur along the southwestern Portuguese coast in small populations, which in addition to phenological differences that occur along the north–south gradient could create a pattern of genetic isolation. To evaluate the degree of genetic diversity and estimate the relationship between population fragmentation and genetic variability, we analysed the five known populations of S. rothmaleri using random amplified polymorphic DNA. Degree of polymorphism and Shannon Index of phenotypic diversity revealed high levels of diversity, found mainly within populations. PCo and cluster analysis revealed a distinct north–south cline, which was confirmed by spatial autocorrelation (Mantel) analysis. This indicates the existence of gene flow between small nearby populations and its insufficiency between widely separated populations. Levels of gene flow (Nm) estimated from the Shannon Index reveal a pattern consistent with a larger past distribution that went through a period of contraction and lack of gene flow followed by population differentiation. The central and largest population probably acts as a core of genetic variability inherited as a relict from a larger and more diverse ancestral population.     

Early blooming's challenges: extended flowering season, diverse pollinator assemblage and the reproductive success of Gynodioecious Daphne laureola

BACKGROUND AND AIMS: The scarcity and unpredictability of active pollinators during late winter in temperate areas tends to favour extended flowering seasons and increased floral longevity in early blooming species, which are usually pollinated by diverse sets of insects. Daphne laureola is a gynodioecious woody perennial that flowers from January to April in southern Spain, a period characterized by cold temperatures, frequent rains and irregular snowfalls. METHODS: Pollinators were excluded at four different times during the flowering season in order to determine the effect of decreased exposure to pollinators on fruit set in female and hermaphrodite individuals. The role of nocturnal and diurnal pollination on reproductive success in each gender was simultaneously evaluated by selective exclusion. KEY RESULTS: A 50 % reduction in the flowering period decreased fruit set of females by 50 %, whereas the corresponding decrease in self-compatible hermaphrodites was only approx. 25 %. Day-active hymenopterans and lepidopterans were infrequent visitors, and nocturnal pollinators were inefficient, suggesting that pollen beetles, Meligethes elongatus, were the main pollinators of D. laureola in the study region. CONCLUSIONS: Beetles were less abundant in pollenless females, although discrimination did not apparently result in pollination limitation of female reproduction. A preference of beetles for sunny locations emphasized the relevance of abiotic conditions for pollination of this early blooming shrub.     

Nectar Dynamics and Sugar Composition in Flowers of Silene and Saponaria Species (Caryophyllaceae)

Abstract: Nectar production in Saponaria officincilis and in five species of Silene (S. ciba, S. dioica, S. noctiflora, S. nutans, S. vulgaris ) was examined during two consecutive years (May to July 1993, and May to June 1994) in the Botanical Garden of the University of Giessen. Nectar volume and sugar concentration were studied in relation to time of day, flower sex, flower age, and flowering stage. Nectar amount in all species studied (except S. dioica ) increased in the afternoon or in the evening until midnight (or until the early morning in S. nutans ). After midnight and until midday, nectar volume in non-visited flowers (except S. dioica ) decreased. Nectar volume in non-visited S. dioica flowers increased constantly with flower age, indicating a stable nectar secretion rate, possibly favouring both day- and night-active flower visitors. Even at the time of highest nectar secretion, all species studied presented several nectarless flowers. Sucrose dominance in the nectar of the nocturnal species S. nutans and Saponaria officinalis fits well with the general syndrome of flowers pollinated by hawkmoths. The syndrome also applies to the nocturnal but regularly selfing, S. noctiflora . The more generalis-tic species S. dioica and S. vulgaris , which are regularly visited by bumblebees as well as nocturnal moths, secreted hexose-domi-nant nectar. Unexpectedly, Silene alba , the only nocturnal species that strictly excluded day-active flower visitors by closing flowers during the day, also secreted hexose-dominant nectar. In some cases, nectar volumes and nectar concentration differed significantly between hermaphroditic, male, and female flowers. Female flowers of S. alba, S. dioica , and S. nutans contained significantly less concentrated nectar than male or hermaphroditic ( S. nutans ) ones. In S. noctifiora and S. vulgaris the difference was not statistically significant but nectar concentration did show the same tendency.     

Isolation and characterization of highly polymorphic microsatellite loci in the bladder campion,Silene vulgaris (Caryophyllaceae)

This study reports the isolation and characterization of seven highly polymorphic microsatellite loci in Silene vulgaris (Caryophyllaceae). The loci were isolated from two libraries constructed from genomic DNA enriched for CA and GA repeats. These markers yielded nine to 40 alleles per locus (mean 22.1) in a survey of 45 individuals from a single population located in the western Swiss Alps. Average observed heterozygosity ranged from 16.2 to 77.4%. These microsatellite loci should be valuable tools for studying fine‐scale genetic structure.     

Effects of fire on the demography of the endangered,geophytic herb Silene spaldingii (Caryophyllaceae)

Understanding the effects of disturbances such as fire on plant demography helps elucidate the mechanisms that cause changes in community composition. I studied the effects of spring and fall fires on Silene spaldingii, an endangered perennial herb of grasslands in northwest Montana. Individual S. spaldingii plants were mapped, and size and flowering were recorded for 1 yr prior and 5 yr subsequent to the burn treatments. Enhanced seedling recruitment (70–410%) and a 22% increase in population size were the principal effects of fire on S. spaldingii, and fall burn plots had lower recruitment than spring burn plots. These effects were apparent for 2–3 yr following the treatments. Fire had no detectable effect on the survival of adults or recruits of S. spaldingii. Silene spaldingii exhibits prolonged dormancy in which plants do not produce aboveground vegetation for one to several consecutive years. Results suggest that fire has a positive effect on the population dynamics of S. spaldingii by removing litter and creating safe sites for recruitment. Prescribed fire should be an important tool for managing populations of this rare plant.     

Climate and clinal variation in seed morphology of the white campion, Silene latifolia (Caryophyllaceae)

Silene latifolia (white campion) is widespread in W Eurasia and shows clinal variation in seed morphology. Two extensive parapatric races, within which seed morphology changes gradually with geographic distance, are separated by a transition zone where the morphological gradient is steeper. A sample of seeds from across the species' native range was scored for morphological characters and analysed using detrended correspondence analysis ordination and multiple regression, in order to simplify mapping of the variation pattern and to investigate statistical relationships with climatic variables. The transition zone, as defined by ordination scores, follows the convolutions of the 0C isotherm for January mean temperature along its entire length from N Europe to the Middle East. January temperature proved to be a highly significant predictor of seed morphology even after the removal of simple spatial trends. Although the origins of comparable large-scale clines have often been interpreted in historical terms, the result reported here supports a role for climatic selection in maintaining the existing variation pattern.     

Pollination and Breeding System of two Co-Occurring Hirtella Species (Chrysobalanaceae) in Central Brazil

The phenology, major floral characteristics, breeding systems and fruiting success of two co-occurring species of Hirtella: H. glandulosa and H.gracilipes (Chrysobalanaceae) were studied in Central Brazil. The two species occur as trees in mesophyllous forests but H. glandulosa is frequent also in dense savanna areas. Both species flower at the end of the dry season (September) and have flowers with one-day longevity. In both species flowers produce nectar and are pollinated exclusively by butterflies. The number of visits recorded and pollination rate in each species were significantly different and indicate that pollinators prefer H. glandulosa flowers. Natural and controlled fruit sets were low in both species. The index of self-incompatibility (ISI) was 0.17 in H. glandulosa and 0.86 in H. gracilipes. Although ISI in H. glandulosa could denote an incompatibility system, the presence of fruits with aborted embryos at different degrees of development point to an inbreeding depression situation. Low pollen viability and fruit set in H. gracilipes suggested reproductive problems which may be linked to hybridization events.     

Reproductive Biology of an Amphicarpic Annual, Polygonum thunbergii (Polygonaceae): Spatio-temporal Changes in Growth, Structure and Reproductive Components of a Population over an Environmental Gradient

Abstract The process and mechanisms of spatio-temporal changes in growth, population structure, as well as various yield and reproductive components of a population of an amphicarpic annual, Polygonum thunbergii (Polygonaceae), with two reproductive systems (aerial chasmogamous flowers and subterranean cleistogamous flowers) along an environmental gradient (light, moisture and soil nitrogen levels) were investigated in the field.
The results clearly demonstrate that growth and allocation patterns, population structure, and reproductive output of individuals changed sharply along the environmental gradient in response to seasonal and spatial changes in resource availability. Models predicted that light conditions bring about one-sided competition, whereas nutrient conditions in the soil engender two-sided competition. As expected, the degree of one-sided competition was prominent in the case of a planophile, Polygonum thunbergii. Allocation patterns, seed outputs, individual seed size as well as relative energy costs of chasmogamous and cleistogamous seed as affected by light and nutrient levels were also critically analyzed. The most noteworthy finding was that the size of chasmogamous seeds sharply decreased in response to a decrease in the light regime, while cleistogamous seed size remained constant along the gradient. However, relative cost of both chasmogamous and cleistogamous seeds sharply increased with decrease in the light level, reflecting different degrees of environmental stress, biotic interference, or both.     

Population genetic structure of Monimopetalum chinense (Celastraceae), an endangered endemic species of eastern China

BACKGROUND AND AIMS: Monimopetalum chinense (Celastraceae) standing for the monotypic genus is endemic to eastern China. Its conservation status is vulnerable as most populations are small and isolated. Monimopetalum chinense is capable of reproducing both sexually and asexually. The aim of this study was to understand the genetic structure of M. chinense and to suggest conservation strategies. METHODS: One hundred and ninety individuals from ten populations sampled from the entire distribution area of M. chinense were investigated by using inter-simple sequence repeats (ISSR). KEY RESULTS: A total of 110 different ISSR bands were generated using ten primers. Low levels of genetic variation were revealed both at the species level (Isp=0.183) and at the population level (Ipop=0.083). High clonal diversity (D = 0.997) was found, and strong genetic differentiation among populations was detected (49.06 %). CONCLUSIONS: Small population size, possible inbreeding, limited gene flow due to short distances of seed dispersal, fragmentation of the once continuous range and subsequent genetic drift, may have contributed to shaping the population genetic structure of the species.     

Self-pollination in Euphrasia willkommii Freyn (Scrophulariaceae), an endemic species from the alpine of the Sierra Nevada (Spain)

 The reproductive ecology of Euphrasia willkommii (Scrophulariaceae), an endemic species from the Mediterranean alpine environments of the SE Spain, has been experimentally studied during two reproductive seasons. The flowers of this plant species were visited by very few insects belonging only to two generalist taxa, thrips and ants. Nevertheless, reproduction is not pollen limited in E. willkommii. Hand-pollinations demonstrated that this plant species is capable of selfing, reproductive success being similar in autogamous and allogamous crosses. Moreover, pollinator-exclusion experiments also showed that, under natural conditions, this plant relies predominantly on selfing, seed production being similar in presence or absence of pollinators. Selfing in E. willkommii is presumably an ecological mechanism to ensure successful reproduction in a harsh environment where pollinator availability is extremely low. Received May 2, 2001 Accepted December 6, 2001     

重庆特有濒危植物缙云黄芩的繁育系统研究

缙云黄芩（Scutellaria tsinyunensis）为重庆市缙云山特有分布种,目前已经处于濒危状态。本文在定点观测的基础上,运用过氧化氢检测法、花粉-胚珠比（P/O）和套袋实验等方法对缙云黄芩的开花特征和繁育系统进行了分析。结果表明：缙云黄芩花展示和花设计具有适合蜂类等传粉昆虫的传粉综合征,熊蜂(Bombus)和食芽蝇为主要的访花者,P/O为7 618±390,繁育系统为专性异交,传粉套袋实验也证实其必需传粉者异花传粉且可能自交不亲和;其雌雄蕊紧靠的花部结构及花粉活力和柱头可授性低、昆虫的访花频率较低等内外因素致使其自然坐果率较低(20.08%)且结实少(5.6个/株)。由于缙云黄芩小坚果萌发率较低,其有性生殖能力较低,居群扩大困难,应尽快采用人工栽培助其复壮等保护措施。     

Reduced Genetic Diversity and Effective Population Size in an Endangered Atlantic Salmon (Salmo Salar) Population from Maine, USA

Atlantic salmon (Salmo salar) populations in Maine, USA, are listed as a Distinct Population Segment under the U.S. Endangered Species Act due to reduced spawning runs and juvenile densities. Whenever possible, optimal conservation strategies for endangered populations should incorporate both present and historical knowledge of genetic variation. We assayed genetic diversity at seven microsatellite loci and at the mitochondrial ND1 gene in an endangered wild population of Atlantic salmon captured from the Dennys River from 1963 to 2001 using DNA’s extracted from archival scale and tissue samples. We examined temporal trends of genetic diversity, population structure, and effective population size (Ne). Overall temporal trends of diversity and Ne show significant reductions from 1963 to 2001 raising the possibility that current restoration efforts may be impacted by historical loss of diversity potentially critical to adaptation. Although our results suggest genetic stability in this population from 1963 to 1981, significant differentiation was observed for both the 1995 and 2001 samples compared with all other temporal samples. The presence of an ND1 mtDNA haplotype in this population, historically observed only in European and Newfoundland stocks, may represent previously unrecognized local wild diversity or, alternatively, may represent introgression from non-native fish.     

Breeding system, flower visitors and seedling survival of two endangered species of Helianthemum (Cistaceae)

BACKGROUND AND AIMS: Helianthemum marifolium and H. caput-felis are two endangered plant species of the western Mediterranean. Several aspects of the reproduction of both species were examined to determine whether their rarity could be related to factors causing reproductive limitation. METHODS: The flowering and fruiting phenology of both species in two non-sympatric island populations (Mallorca, Balearic Islands, western Mediterranean) were compared. Hand-pollination experiments were conducted to determine their fruit and seed production under different pollen sources. The composition of the pollinator assemblage and the effect of temporal variation and sun exposure on reproductive output and seedling survival were also investigated. KEY RESULTS: Flowering periods were longer for H. marifolium than for H. caput-felis in the populations studied. Helianthemum marifolium is mostly an outbreeder, i.e. fruit and seed set was three-fold higher when pollen came from other plants. In H. caput-felis, neither fruit nor seed set was affected by pollination treatments. Flower visitors were more diverse for H. caput-felis than for H. marifolium. In both species, most floral visits were made by hymenopterans. The total number of pollinator visits varied significantly between years, decreasing more than two-fold from 2001 to 2002, in both species. In agreement with its outbreeder character, variation in reproductive output between years was also observed in H. marifolium. It showed a 50 % decrease in fruit set in 2002, a pollinator-poor year. Finally, seedling survival increased three- to six-fold from 2001 to 2002. A correlation between seedling size and survival had also been detected. CONCLUSIONS: Reproductive limitations were detected for neither species (i.e. fruit and seed set, pollination service and seedling survival on natural populations). Hence, the increasing rarity of these two species is probably a direct result of the destruction of their habitat.     

Population structure,growth and fecundity of perch (Perca fluviatilis L.) in an acidified river system in Southern Norway

Population structure, density and reproductive potential of perch (Perca fluviatilis L.) from 4 acidified lakes in a river system in Southern Norway were investigated. The upper 3 lakes were most affected by acidification and the number of perch caught per unit effort indicate three-fold increase in density from the upper Gjerstadvann to the lower Brøbørvann. Low density of perch in the upper lakes is explained by; 1) Abnormal mortality occurring in episodes due to acidification, probably caused by aluminium toxicity at pH = 5.2–5.4. 2). Acid water (pH ≤ 5.0) during spawning and development of eggs and larvae, resulting in recruitment failure. Juvenile mortality of perch may depend on the density of the parental stock. In the 3 upper lakes, the density of adult perch probably was too low to produce significant juvenile mortality, and in these lakes the recruitment probably depended more on the May water quality. Improved water quality increases egg hatching and survival and also benefits zooplankton production, the main food for perch during the first summer. Low population density has reduced competition for food and thus improved growth of perch in the 3 upper lakes compared to the lower lake. The perch in Brøbørvann mature at higher age and have lower individual fecundity than perch in Gjerstadvann, an effect of both slower growth and lower length specific fecundity in Brøbørvann. In Gjerstadvann, the perch therefore have a higher reproductive potential relative to the stock density, and may, when the water quality is good enough, give rise to strong year-classes and more frequent year-class fluctuations than perch in the less acid Brøbørvann.