Holocrine secretion and cytoplasmic content of Helleborus foetidus L. (Ranunculaceae) nectar

We used electron microscopy to investigate the fine structure of nectary secretions of Helleborus foetidus. During the secretion period, epidermal cells of nectaries discharge the whole contents of the cytoplasm into the nectary cavity. The external wall of the cell breaks, releasing the cytoplasm as a dense aggregate that later disperses in the nectary cavity. Cell components, such as chromatin, plastids, mitochondria, lipid droplets and membranes, were found in the nectar of H. foetidus, evincing the complex nature of the secreted material. These results confirm that nectar secretion in H. foetidus is of the holocrine type.     

Inter- and intra-floral heterogeneity of nectar production in Helleborus foetidus L. (Ranunculaceae)

Three southern Spanish populations of Helleborusfoetidus L. (Ranunculaceae) were sampled for nectar content in the absence of nectarivorous flower visitors. Nectar volume was measured in individual nectaries of flowers at the same stage in the anthesis cycle. Total nectar content per flower was extremely variable between plants within populations and between flowers within plants, but much less so between populations. Average sugar content per flower was roughly similar in the three populations sampled. High variances in nectar abundance occurred also among nectaries within the same flower. Heterogeneity in pollinator rewards thus occurs simultaneously at several spatial scales, namely between nectaries, between flowers and between plants. This implies a strong component of uncertainty to foraging pollinators, which may therefore tend to avoid Helleborus flowers.     

Floral integration,phenotypic covariance structure and pollinator variation in bumblebee‐pollinated Helleborus foetidus

By analysing patterns of phenotypic integration and multivariate covariance structure of five metric floral traits in nine Iberian populations of bumblebee‐pollinated Helleborus foetidus (Ranunculaceae), this paper attempts to test the general hypothesis that pollinators enhance floral integration and selectively modify phenotypic correlations between functionally linked floral traits. The five floral traits examined exhibited significant phenotypic integration at all populations, and both the magnitude and the pattern of integration differed widely among populations. Variation in extent and pattern of integration was neither distance‐dependent nor significantly related to between‐population variation in taxonomical composition and morphological diversity of the pollinator assemblage. Patterns of floral integration were closer to expectations derived from consideration of developmental affinities between floral whorls than to expectations based on a pollinator‐mediated adaptive hypothesis. Taken together, results of this study suggest that between‐population differences in magnitude and pattern of floral integration in H. foetidus are probably best explained as a consequence of random genetic sampling in the characteristically small and ephemeral populations of this species, rather than reflecting the selective action of current pollinators.     

Breeding systems in two species of the genus Helleborus (Ranunculaceae)

ABSTRACT

The results of various types of manual and free pollination are reported in Helleborus bocconei and Helleborus foetidus, two sympatric species of the understorey of submediterranean woods that flower in January–March and are pollinated by bumble-bees of the genus Bombus. Both species were found to be partially self-compatible even if at different rates; geitonogamy seems to be more frequent in H. foetidus and spontaneous self-pollination does not usually occur for morphological reasons, and the species are not apomictic. Efficiency in seed production after free pollination was very high indicating that in spite of harsh climatic condition, there were no limitations imposed by pollen or pollinators.     

Floral organogenesis of Helleborus thibetanus and Nigella damascena (Ranunculaceae) and its systematic significance

Floral organogenesis in Helleborus thibetanus and Nigella damascena was examined and compared using scanning electron microscopy and light microscopy, and the putative relationships of Helleborus and Nigella were analysed. H. thibetanus and N. damascena share some features of floral phyllotaxis and development of the sepals, petals, stamens and carpels, which are also found in other members of Ranunculaceae. However, they differ strongly in the number and degree of fusion of the carpels: in H. thibetanus, the two carpels are slightly united at the base, whereas, in N. damascena, the gynoecium is syncarpous and the five carpels are united throughout the ovary. Differences are also noted in petal development. The blade of the young petal of H. thibetanus develops two bulges which become connate and then fuse with the blade at the sides, developing more quickly than the blade and forming a tubular petal. In N. damascena, a single ridge is formed on the petal blade which develops into the smaller adaxial labium of the bilabiate petal, whereas the blade itself develops into the larger abaxial labium bearing two pseudonectaries. The outermost stamens are delayed in development in Helleborus, but not in Nigella. Although the results from our investigation are preliminary, differences in floral development characters suggest that Helleborus and Nigella may not be closely related and possibly support placement into separate tribes. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 166 , 431–443.     

Effects of variation in flower number on pollinator visits in Cirsium purpuratum (Asteraceae)

We examined the functional relationships between floral display and two types of bumble bee response, the visitation rate per plant and the number of flowers visited on a plant, in an artificially arranged field population of Cirsium purpuratum. To reduce the variance in data, we collected data for each day separately and adopted a Latin square design in selecting the focal plants within a day. We then tested several types of regressions to each set of data to find the best-fitting line accounting for the observed relationship between pollinator response and display size. We found that the visitation rate of bumble bees per plant was a decelerating function of floral display, and that the number of flowering heads visited on a plant increased linearly with display size. Predicted from the above two functions, the visitation rate per head was independent of floral display and nearly constant within each day. Our results suggest that conventional methods in collecting and analyzing data on pollinator visitation may yield large variance in data derived from temporal and spatial heterogeneity and that improved methods employed here are effective in reducing the variance and estimating patterns of pollinator response to floral display more accurately.     

Effect of flower number on the pollinator attractiveness and the threshold plant size for flowering in Pertya triloba (Asteraceae)

Pertya triloba (Asteraceae) is a perennial herb growing in the understory of deciduous broad-leaved forests in central Japan. Its capitulum consists of a single floret that differs from those of most other Asteraceae species. A bagging experiment clearly showed that breeding of P. triloba required cross-pollination. By using female fertility as a measure of pollination success, the effect of an attractive floral display on the threshold plant size for flowering in P. triloba was surveyed. The number of florets per plant in a P. triloba population was artificially adjusted between one and 30. In both control plants and experimental plants with adjusted floret number, the seed set increased with an increase in the number of florets per plant and became constant (60%) when the floret number per plant was more than 10. Thus, the number of florets per plant has an important role in attracting pollinators, and more than 10 florets per plant must be the effective floral display size. In the P. triloba population, 98.5% of the flowering plants had 10 or more flowers. The effective floral display size might be determined through the mutual relationship between plants and pollinators. The number of florets per plant increased with an increase in the plant leaf area. Therefore, the threshold plant size for flowering might be determined by the productivity needed to support an attractive floral display.     

Censusing natural microgametophyte populations: variable spatial mosaics and extreme fine-graininess in winter-flowering Helleborus foetidus (Ranunculaceae)

Little is known about patterns and correlates of variation in microgametophyte populations for naturally pollinated plants, yet this information is critical for evaluating the prevalence and potential evolutionary significance of gametophyte competition in the wild. This paper analyzes spatial and temporal variation in microgametophyte populations (= number of pollen tubes per style) for the winter-flowering, perennial herb Helleborus foetidus (Ranunculaceae), based on data from 29 populations in three regions of the Iberian Peninsula collected over two consecutive years. Mean size of microgametophyte populations varied significantly at a wide range of spatial scales, including among regions, among populations within regions, among individual plants within populations, among flowers of the same plant, and among pistils of the same flower (H. foetidus flowers are apocarpous). Differences between regions were quantitatively negligible. Differences between populations in the same region were moderate to low, and their sign and magnitude were inconsistent between years. Roughly half of total variance in microgametophyte numbers was accounted for by variation within individual plants, and the largest part of this component was due to differences between the pistils of the same flower. These results reveal extreme spatial fine-graininess and marked stochasticity in the spatial variation of H. foetidus microgametophyte populations and suggest that opportunities for consistent selection on male gametophyte competitive ability are probably negligible in this species.     

Variation in structural gender in the hermaphrodite Helleborus foetidus (Ranunculaceae): within- and among-population patterns

In hermaphrodite plants, variations in structural gender (defined as the ratio between male and female gametes) may occur at different levels (among flowers, plants, and populations). In this study, we investigated variation in four traits influencing structural gender (number of carpels, ovules per carpel, stamens, and pollen grains per stamen) within and among six distant populations of the hermaphrodite perennial herb Helleborus foetidus (Ranunculaceae) in the Iberian Peninsula. Our results show that the four traits investigated varied significantly at all levels considered. Traits influencing the female sexual component (number of carpels and ovules per carpel) showed greater variation at the lowermost levels (within flower and plant) than traits influencing the male component, which in turn varied more markedly among populations. Number of carpels per flower and number of pollen grains per anther were the most important traits affecting between-plant variation in structural gender. There was no evidence of significant plant-level trade-offs or correlations between the various male and female traits, which covaried differently across populations. The observed between-population variation in structural gender of Helleborus foetidus can be explained as a consequence of differences in self-pollination levels related to a flowers mating environment.     

毛茛状金莲花不同花期的花特征和访花昆虫的变化及表型选择

为了研究植物生长季内开花时间对花特征表型选择的影响,我们以青藏高原东缘高寒草地的毛茛状金莲花Trollius ranunculoides)为实验材料,在生长季内不同开花时间(花前期、花末期)测定花特征,观察访花昆虫的类群和访花频率,生长季结束后收集种子.根据昆虫访花的喜好和季节内类群与访花频率的变化,分析了不同开花时间毛茛状金莲花的花特征与昆虫的选择;并用种子产量表示雌性适合度,估计了毛茛状金莲花的花特征在不同开花时间所受的表型选择.结果表明:不同花期植物的花特征有显著差异,相应的访花昆虫的类群和频率也存在差异,不同类群昆虫访花喜好也不一样.蜂喜好花瓣和花萼较宽、花茎短和花茎数少的个体,这正符合花前期的特征,因而蜂的访花频率在花前期较高;蝇对花特征没有明显的偏好.而通过雌性适合度估计毛茛状金莲花花特征所受的表型选择则是:花前期,花茎较长和花茎数多的植株适合度大;花末期,花茎数多的植株适合度大.我们的研究表明:在植物生长季,花期的分化伴随着传粉昆虫活动的变化.不同花期,访花昆虫的变化可能对植物花特征的分化起了至关重要的作用.但是访花昆虫对花特征的选择与通过雌性适合度估计植物受到的选择不尽相同,这可能是由于其他因素造成的.     

The geographic mosaic in predispersal interactions and selection on Helleborus foetidus (Ranunculaceae)

We examine the hierarchical geographic structure of the interaction between a plant, Helleborus foetidus, and its floral herbivores and pollinators (interactors). Six populations from three distant regions of the Iberian Peninsula were used to examine intra- and inter-regional variation in plant traits, interactors and plant fecundity, and to compare, through selection gradient and path analyses, which traits were under selection, and which interactors were responsible for differential selection. Geographic and temporal congruency in interactor-mediated selection was further tested using a recent analytical approach based on multi-group comparison in Structural Equation Models. Most plant traits, interactors and fecundity differed among regions but not between populations. Similarly, the identity of the traits under selection, the selection gradients (strength and/or the direction of the selection) and the path coefficients (identifying the ecological basis for selection) varied inter- but not intra-regionally. Results show a selection mosaic at the broad scale and, for some traits, a link of differential selection to trait differentiation.     

Variation in DNA methylation transmissibility,genetic heterogeneity and fecundity‐related traits in natural populations of the perennial herb Helleborus foetidus

Inferences about the role of epigenetics in plant ecology and evolution are mostly based on studies of cultivated or model plants conducted in artificial environments. Insights from natural populations, however, are essential to evaluate the possible consequences of epigenetic processes in biologically realistic scenarios with genetically and phenotypically heterogeneous populations. Here, we explore associations across individuals between DNA methylation transmissibility (proportion of methylation‐sensitive loci whose methylation status persists unchanged after male gametogenesis), genetic characteristics (assessed with AFLP markers), seed size variability (within‐plant seed mass variance), and realized maternal fecundity (number of recently recruited seedlings), in three populations of the perennial herb Helleborus foetidus along a natural ecological gradient in southeastern Spain. Plants (sporophytes) differed in the fidelity with which DNA methylation was transmitted to descendant pollen (gametophytes). This variation in methylation transmissibility was associated with genetic differences. Four AFLP loci were significantly associated with transmissibility and accounted collectively for ~40% of its sample‐wide variance. Within‐plant variance in seed mass was inversely related to individual transmissibility. The number of seedlings recruited by individual plants was significantly associated with transmissibility. The sign of the relationship varied between populations, which points to environment‐specific, divergent phenotypic selection on epigenetic transmissibility. Results support the view that epigenetic transmissibility is itself a phenotypic trait whose evolution may be driven by natural selection, and suggest that in natural populations epigenetic and genetic variation are two intertwined, rather than independent, evolutionary factors.     

Pollination, breeding system, and genetic structure in two sympatric Delphinium (Ranunculaceae) species

Two sympatric Delphinium species, D. barbeyi and D. nuttallianum, are ecologically and morphologically similar. However, D. barbeyi has multiple, large inflorescences while D. nuttallianum has a single, small inflorescence. These differences in floral display should result in greater intraplant pollen transfer in D. barbeyi, leading to higher rates of self-pollination through geitonogamy. Reduced gene flow by pollen should in turn produce greater population differentiation among populations of D. barbeyi relative to D. nuttallianum. We tested these predictions by comparing pollinator behavior, breeding systems, outcrossing rates, and population genetic structure of sympatric populations of the two species in Colorado. Bumble bee and hummingbird pollinators visit more flowers and inflorescences per foraging bout in D. barbeyi than in D. nuttallianum. The species differed in breeding system; D. barbeyi produced more seeds by autogamy (9 vs. 2%) than D. nuttallianum and suffered no reduction in seed set in hand-self vs. outcross pollinations, in contrast to a 41% decline in D. nuttallianum. The outcrossing rate in one D. barbeyi population was 55%, but ranged from 87 to 97% in four D. nuttallianum populations. Genetic differentiation among population subdivisions estimated by hierarchical F statistics was >10 times greater in D. barbeyi ( = 0.055-0.126) than D. nuttallianum ( = 0.004-0.009) at spatial scales ranging from metres to 3.5 km. Spatial autocorrelation analysis also indicated more pronounced local genetic structure in D. barbeyi than D. nuttallianum populations. Fixation indices (F(IS)) of D. barbeyi adults were much lower than expected based on mating system equilibrium and suggest that differences in the degree of self-compatibility and/or the timing of postpollination selection/inbreeding depression between the two species further contribute to the genetic differences between them.     

柴达木盆地荒漠植物功能性状及其对环境因子的响应

植物功能性状是植物适应环境的外在表达,反映了植物在不同环境中的生存策略,探究干旱区荒漠植物功能性状及其与环境之间的关系,有助于理解植物适应极端干旱环境的生态对策,为保护荒漠地区生态系统提供理论依据。以柴达木盆地为研究区,选取8个植物功能性状指标,包含4种植物生活型,10种荒漠植物,探究荒漠植物功能性状的基本特征及其对环境因子的响应。研究表明：柴达木盆地植物叶片碳含量(LCC)、叶片氮含量(LNC)、叶片磷含量(LPC)、叶片C∶N、叶片N∶P、叶片稳定碳同位素(Leafδ¹³C)、叶片干物质含量(LDMC)和植株高度(Height)的变化范围分别为272.07—466.00mg/g、12.40—44.50mg/g、0.51—2.07mg/g、8.62—29.74、11.37—39.29、-27.38‰—-14.80‰、100—480mg/g、3.00—264.22cm。不同生活型间LNC、LPC、叶片N∶P和LDMC差异不显著,LCC、叶片C∶N、叶片δ¹³C和植株高度存在显著差异。LNC、LPC和叶片N∶P与全球、中国和青藏高原相比不存在显...     

Geographic and temporal variation in the ant–seed dispersal assemblage of the perennial herb Helleborus foetidus L. (Ranunculaceae)

Spatio-temporal variations in the composition of the animal interactive assemblages may result in variations in selective pressures on the plants. In ant–seed dispersal mutualisms, the study of the magnitude of spatial and temporal variation of ant assemblages is rarely studied, limiting inferences and generalizations on the evolution of this mutualism. Here, we describe the ant–disperser assemblage of the myrmecochorous herb Helleborus foetidus in 14 populations across the Iberian Peninsula, and dissect the variation in the assemblage into spatial and temporal components as a first step to evaluate the evolutionary potential of this interaction. The ant–visitor assemblage of H. foetidus was mainly represented by species of Formicinae and it was highly diverse and variable in composition and function. Ants behaving as legitimate dispersers and those with mixed behaviour numerically dominated the assemblage compared with elaiosome consumers. The magnitude of the spatial variation was higher than the temporal variation, suggesting that the relative frequency of each functional group will be more foreseeable among years in each population than among populations. At the expense of further analysis of the effects of such variation on dispersal success, we can envisage a selection mosaic scenario, where local adaptive responses of plants might arise as a result of local variations in the specific composition and function of the assemblage.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 135–150.     

Differences in floral traits and flower visitation rates in mating systems in Prunella vulgaris (Lamiaceae)

夏枯草交配系统对花特征和访花频率差异的影响 植物花特征和传粉者的访问次数与交配系统类型密切相关。唇形科植物夏枯草(Prunella vulgaris)存 在两种植株类型,分别为柱头伸出花冠和柱头在花冠内部的植株,而且两种植株的比例在不同种群中存在差异。本研究选择柱头伸出花冠外植株占绝大多数、柱头伸出花冠外植株占多数和柱头在花冠内部植株占多数的3个种群,通过比较每个种群中两种植株类型的开花物候、花形态特征、昆虫访问频率、自交能力、传粉者对结实的贡献以及近交衰退的水平,以检验花特征和传粉者访问次数与交配系统类型的关系。研究结果表明,与柱头在花冠内部的植株相比,柱头伸出花冠外的植株具有更大和更多的花,产生更多的花粉和花蜜,具有更高的访花频率,并主要通过异交产生种子。在种群水平,柱头伸出花冠外的植株占多数种群的访花频率显著高于柱头在花冠内部植株占多数的访花频率。柱头在花冠内部的植株比柱头伸出花冠外的植株具有更强的自动自交能力,在传粉者缺乏时为其提供了繁殖保障,但繁殖保障和异交率在不同种群中差异不显著,表明较低的昆虫访问能够满足夏枯草的授粉需求以产生种子,这可能与夏枯草较少的胚珠数量(每朵花仅有4个胚珠)有关。柱头在花冠内部植株的近交衰退水平低于柱头伸出花冠外植株的近交衰退水平,但两种植株类型的近交衰退水平均低于0.5,说明近交衰退不足以阻止该物种中自交的进化。综上所述,柱头在花冠内部的植株能够通过自交为夏枯草提供繁殖保障,而柱头伸出花冠外的植株能够利用昆虫传粉确保异交,表明混合交配系统在该物种中是一个稳定的状态。