Intra-inflorescence variation in floral traits and reproductive success of the hermaphrodite Silene acutifolia

BACKGROUND AND AIMS: Intraspecific variation in floral components and reproductive success is often located at the intra-individual level. The arrangement of flowers within inflorescences may explain a great deal of this variation. The variation in number of ovules, fruit set, number of seeds per fruit, seed set, seed weight and seed germination is investigated at different positions within the inflorescence of Silene acutifolia. METHODS: Data were obtained in natural populations, and germination experiments were conducted in a germination chamber. KEY RESULTS: The number of ovules, fruit set, number of seeds, seed set and seed weight, showed a significant decline from early (primary) position to later (tertiary) position. The patterns of intra-inflorescence variation were consistent in different populations and years of study. Seed germination showed an opposite pattern, seeds from primary position showed the lowest germination percentages and seeds from tertiary position the highest, although the effect of position on germination was only marginally significant. There was significant among-population variation in number of ovules per flower. Fruit set also varied significantly among populations, with lower fruit set in the smaller and more isolated population. No significant among-population differences were detected in number of seeds per fruit and seed set. Seeds from the smallest and more isolated population (Arnado) were the lightest. Seed germination showed strong differences between populations, seeds from Arnado started to germinate later, and showed the lowest final germination percentages. CONCLUSIONS: Architectural effects or resource competition are the most commonly proposed hypothesis to explain these patterns. Data suggest that there is less pollen available to pollinate tertiary flowers, and that there is not enough outcross pollen in Arnado. The germination percentages suggest that there is variation in the source of pollen within inflorescences, with high probability of receiving outcross pollen in flowers from primary position, and higher probability of geitonogamous crosses in tertiary flowers.     

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.     

Pollination and seed predation by moths on Silene and allied Caryophyllaceae: evaluating a model system to study the evolution of mutualisms

Nursery pollinators, and the plants they use as hosts for offspring development, function as exemplary models of coevolutionary mutualism. The two pre-eminent examples--fig wasps and yucca moths--show little variation in the interaction: the primary pollinator is an obligate mutualist. By contrast, nursery pollination of certain Caryophyllaceae, including Silene spp., by two nocturnal moth genera, Hadena and Perizoma, ranges from antagonistic to potentially mutualistic, offering an opportunity to test hypotheses about the factors that promote or discourage the evolution of mutualism. Here, we review nursery pollination and host-plant interactions in over 30 caryophyllaceous plants, based on published studies and a survey of researchers investigating pollination, seed predation, and moth morphology and behavior. We detected little direct evidence of mutualism in these moth-plant interactions, but found traits and patterns in both that are nonetheless consistent with the evolution of mutualism and merit further attention.     

Pollination ecology of the pre-Pyrenean endemic Petrocoptis montsicciana (Caryophyllaceae): effects of population size

Petrocoptis montsicciana (Caryophyllaceae) is a threatened pre‐Pyrenean endemic that grows exclusively on caves and walls of limestone. We studied its pollination ecology by monitoring phenology and by evaluating pollen and nectar production, pollinator activity (frequency and behaviour of visitors), quantity and quality of pollination services, pollen/ovule ratio, and seed set in response to insect exclusion and self‐compatibility tests. We also analysed the effect of population size on reproductive mechanisms by comparing a large and a small population. Flowers of P. montsicciana produced nectar and were visited by Hymenoptera (79.7%), Diptera (11.5%), and Lepidoptera (8.8%). The most frequent pollinators (60.6% of total visits) were long‐tongued bees of the genus Anthophora. Both populations had a similar range of pollinators. We found a correlation between the number of visited flowers and the number of open flowers per census; 88.7% of pollen grains deposited on the stigmas were conspecific and the main competitor was another chasmophyte plant, Antirrhinum molle. Bagged flowers set seeds but significantly less so than hand‐self‐pollinated and control flowers. Thus, although self‐compatible and self‐pollinated, entomophilous pollination of P. montsicciana is required in order to explain c. 10–40% of total seed set, in accordance with P/O ratio estimations. Bagged flowers from the small population set significantly more seeds than the large one. Visitation rates were lower in the small population, but, unexpectedly, showed higher stigmatic pollen loads and similar or higher seed set. These results suggest an increase of spontaneous selfing rates in the small population, probably favoured by a smaller flower size, which can not only assure reproductive success when pollinators are scarce, but also provide additional potential to adapt to climatic changes. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76 , 79–90.     

开花式样对传粉者行为及花粉散布的影响

理解植物花的特征可以从单花特征和群体特征两个层次入手。开花式样是植物的花在群体上的特征体现, 通过在开花数目、开花类型以及花的排列上的变化, 不同的开花式样对传粉者具有不同的吸引力, 影响昆虫在植株上的活动, 使花粉运动的方向发生相应变化, 从而影响着植物最终的交配结果。此外开花式样随环境改变也会发生一些变化。本文介绍了开花式样研究的进展, 对开花数目、开花类型以及花的排列等3个方面的已有研究进行了分别阐述, 并提出开花式样研究应更多地考虑影响传粉的各种因素。     

Functional differentiation in pollination processes among floral traits in Serapias species (Orchidaceae)

Floral displays, influencing attractiveness to insects, increase the number of pollinator visits and the efficiency of each visit in terms of pollen exchange and thus affect the plant reproductive success. Here, we conducted an in situ manipulation experiment to investigate whether the floral modifications affect reproductive success in natural orchid populations of Serapias lingua and Serapias vomeracea. We estimated male and female reproductive success of three treatment groups, disassembly of floral tube, cutting of lip, and painting of the callus surface, in terms of pollinaria removed/deposited and fruit production. Results revealed that phenotypic modification had opposite effects on reproductive success of two examine species. Indeed, reproductive success was significantly increased by the detached of the petals and sepals, and decreased, due to callus painting and lip removal, in S. lingua. On the contrary, unmanipulated plants of S. vomeracea showed significantly higher value of pollinaria removed and deposited and fruit set than manipulated ones. The differences between S. lingua and S. vomeracea agree to the different pollination strategy of examined species. S. vomeracea shows shelter imitation strategy, and thus, the disassembly of tunnel‐like corolla does not allow the insects to use the flower as a refuge, while S. lingua is a sexually deceptive orchid and therefore the opening of the flower made more visible callus (visible at a greater distance) increasing the pollinators attraction. This study provides evidence that pollinators were largely sensitive to the experimental modification of the flower phenotype, which is consistent with the presence of significant selection on individual floral characters. Our experimental investigations of the effects of variation in display on pollinator visitation provide insights into the evolution of floral morphology in orchid with shelter imitation strategy.     

Reproductive success and variation in floral traits in the Iberian Peninsula endemic white campion <Emphasis Type="Italic">Silene marizii</Emphasis> (Caryophyllaceae)

Silene marizii (Caryophyllaceae) is a schizoendemism of the west Iberian Peninsula. The correlation between the evolution of reproductive success (as measured in terms of fruit set and seed production) and five floral traits (peduncle length, calyx length, calyx width, petal limb length, and petal limb width) was investigated in five populations of S. marizii, taking into account both intra-populational and inter-populational variability. The populations studied represented the different habitats of S. marizii over its area of distribution. None of the five traits examined was significantly and positively correlated with the number of seeds produced by the flower. An analysis was also made of how floral morphology varies with the position of the flower in the inflorescence in the five populations. The populations from higher altitudes (Caramulhino, Puerto de Menga and Peña de la Cruz) had larger peduncles, calices and petal limbs than those living at lower altitudes (Sabugal and Mangualde) All five morphometric traits, plus the number of ovules per ovary, varied significantly between flower positions on the same plant and among populations.     

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.     

Taking a chance on moths: oviposition by Delia flavifrons (Diptera: Anthomyiidae) on the flowers of bladder campion, Silene vulgaris (Caryophyllaceae)

Abstract.

• 1 Delia flavifrons Zetterstedt (Diptera: Anthomyiidae) visits flowers of Silene vulgaris (Moench) Garcke (Caryophyllaceae), where the adults feed, mate, lay their eggs, and the larvae feed on developing seeds. The objective of the study was to examine how an ovipositing female fly assures a food resource for her progeny.
• 2 Ovipositing females preferred young, non-pollinated flowers over older pollinated ones. The flies did not pollinate the flowers and survival of the larvae depended on the flowers being pollinated by moths.
• 3 Flowers containing fly eggs were pollinated more often than expected from chance, probably as a result of both flies and moths visiting particular flowers.
• 4 Eggs were laid singly, and multiple oviposition occurred randomly. Although most eggs hatched, only about half produced larvae that made their way into the fruits. As a result, the probability of competition arising from multiple oviposition may be reduced to such an extent that selection does not favour females that avoid flowers with conspecific eggs.
• 5 Moth larvae of the noctuid genus Hadena also feed on the seed pods of S. vulgaris and will kill any fly larvae they encounter. However, there was no deviation from random oviposition by the flies in relation to eggs laid by the moths, but the competitively weaker fly usually started to lay eggs towards the end of the moth's egg-laying period.
• 6 The relationship between Delia flavifrons and Silene vulgaris superficially parallels that for known pollinator/predator systems, but floral adaptations to hypothetically pollinating flies seems not to have taken place.

     

The spatial distribution of chloroplast DNA and allozyme polymorphisms within A population of Silene alba (Caryophyllaceae)

Genetic structure within a population of Silene alba was studied using a chloroplast DNA (cpDNA) and six allozyme polymorphisms. A 20 × 65 m area was sampled by constructing a 5 × 5 m grid and determining the genotype of the plant nearest to each grid node. Analysis of the spatial distribution of genotypes by Moran's I and join-counts showed a significant degree of association of like cpDNA haplotypes (I = 0.52, S.N.D. = 2.55) but a random or slightly repulsed distribution of allozyme genotypes. A second sample was taken by collecting all individuals from within a 1-m wide transect established along the perimeter of the grid. Genotype and allele frequencies were calculated by grouping individuals from arbitrary 3-m intervals along the transect, and analyzed by Wright's F statistics. The F_st value calculated for cpDNA (0.875) differed markedly from that based on all allozymes (0.027). Taken together, the results suggest that in this population gene flow in the maternally inherited cpDNA is limited by restricted seed dispersal, whereas gene flow in the nuclear DNA based allozymes is more pervasive owing to the added effects of pollen dispersal. The utility of cpDNA polymorphism for the study of fine-scale gene flow is discussed.     

Experimental taxonomy of Silene section Elisanthe (Caryophyllaceae): crossing experiments

Silene section Elisanthe is a well-defined group containing (in Europe) the following species: S. alba, S. diclinis, S. dioica, S. heuffelii and S. marizii (dioecious perennials or biennials) and S. noctifloara (a self-compatible hermaphrodite annual). Crosses were attempted among these species, and between these species and members of other Silene sections.
Crosses among the first five species revealed partial cross-incompatibility with moderate hybrid fertility. S. alba proved especially incompatible with S. diclinis. S. noctiflora would not cross at all with other members of the section. It is suggested that S. noctiflora evolved from a dioecious precursor of S. alba , the species to which it is most similar in morphology, distribution and habitat; hybrid sterility, even without incompatibility, would have assured mutual isolation.
Crosses with species from other sections of Silene have usually either failed consistently or revealed high cross-incompatibility with hybrid sterility. Those crosses which were successful have all been within the boundaries of the old genus Melandrium , or with Lychnis species.     

Pollination ecology of Gentiana siphonantha (Gentianaceae) and a further comparison with its sympatric congener species

In this study, we studied pollination ecology of Gentiana siphonantha (Gentianaceae), a late-autumn flowering alpine perennial in the northeastern Qinghai-Tibetan Plateau for two years for the first time. We also aimed to compare the pollination differentiation between this species and sympatrically distributed G. straminea that has a close phylogenetic origin but is flowering early. Flowers of G. siphonantha are characteristic of di-chogamy and herkogamy and this floral development prevents occurrence of autonomous self-pollination. This implication was confirmed by the breeding experiments, since no seed was produced when flowers were isolated. However, this gentian proved to be highly self-compatible when geitonogamous selfing was artificially induced. Each individual plant of this species has an average of 14.6 flowers ranging from 4 to 31, at both staminate and pistillate stages with a ratio of 1.2:1 in full anthesis. Both floral development and breeding experiments suggested that pollen vectors were indispensable for successful seed sets of this species. A great variety of insects were observed to visit this species, but the most common and only legitimate pollinator is Bumbus sushikini. A statistic observation suggested that this pollinator showed no preference to either staminate or pistillate flowers and visited them at random. We further calculated the frequency of their visits between and within individual plants. Among the pollinators’ bouts, the proportions of geitonogamous visits within an individual plant occupy about 87.8%. Such a case implied that geitonogamous selfing prevails in this species in spite of floral dichogamy and her-kogamy that were suggested to promote outcrossing. Compared with sympatric G. straminea, the total floral longevity and the male and female duration of this species are shorter. However, the number of flowers of each individual plant and branch increased when in full anthesis. It is interesting that both closely related species shared the same pollinator despite their distinct difference in flower morphology. This finding is inconsistent with the previous hypothesis that both flower color and corolla tube depth have coevolved with different pollinators during speciation and formation of reproductive isolation. Both visit frequencies of the individual flower and geitonoga-mous visits within the individual plant are higher in G. siphonantha than in G. straminea. This difference may result from their different inflorescence designs that actively act upon behaviors of pollinator. Although these two species differed in flowering phenology, their flowering stages overlapped for a few days, suggesting incomplete pollination isolation between them.     

Numerical analysis of infraspecific variation in European Silene alba and S. dioica(Caryophyllaceae)

Infraspecific variation among European populations of Silene alba and S. dioica was analysed by non-metric multidimensional scaling, which was applied to K-dissimilarity matrices based either on 16 seed characters or on 34 seed, flower and capsule characters. The material used for analysis consisted of 167 collections of wild seed, largely obtained from European botanic gardens, and 97 sets of mature greenhouse-grown progeny. S. alba was found to show topoclinal variation, primarily along an axis from the Iberian peninsula through central Europe to Romania. This pattern is not reflected in current taxonomic treatments. N. and N.W. European S. alba is morphologically heterogeneous and has probably been introduced from various southern sources. S. dioica shows less total variation between populations than S. alba , and consists of local ecogeographic races that intergrade at their margins. The two species are completely discriminated by seed, flower and capsule characters when used in combination, but S. alba populations from the eastern end of the cline closely approach S. dioica in seed morphology. This convergence is unlikely to be an effect of recent introgression.     

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.     

Population Size,Pollination and Breeding System of Silene stockenii Chater (Caryophyllaceae), an Annual Gynodioecious Species of Southern Spain

The distribution area, phenology, sex polymorphism, floral characteristics and breeding system of Silene stockenii (Caryophyllaceae), a narrowly endemic annual species of southern Spain, were studied. Only five populations were found in a total area of 2 ha. Silene stockenii is a gynodioecious species with fully female, fully hermaphrodite and intermediate plants bearing hermaphrodite, male-sterile, and partially male-sterile flowers. Male-sterile flowers are typically smaller than hermaphrodites. Nectar production was significantly higher in hermaphrodite plants and during the female phase of hermaphrodite flowers. The red flowers appear during the spring (March-May) and are pollinated by long-tongued Bombyliidae. Hand pollinations revealed that the species is self-compatible; however, natural self-pollination is rare due to marked protandry. Hand pollination significantly increased the number of seeds per fruit and seed set, indicating limited pollination in the field. In controlled pollinations female plants of S. stockenii produced higher seed set than hermaphrodite plants, but in freely pollinated plants fruit set and seed production was similar in both morphs, indicating that pollinators do not discriminate in favour of hermaphrodite plants.     

Pollination by deceit in nutmeg (Myristica insipida, Myristicaceae): floral displays and beetle activity at male and female trees

Pollination by deceit in Myristica insipida, a beetle-pollinated nutmeg, was hypothesized to operate on intersexual differences in flower production and longevity, producing a daily fluctuation between floral display maxima and minima. Sticky traps were used to continuously monitor beetle activity. Flower production and naturally occurring intersexual differences in display were recorded. Male and female trees flowered in synchrony producing daily display maxima at 1800-0600 and display minima at 1400-1800. Rewarding male trees produced three times the number of flowers of female trees, but the greater longevity of female flowers reduced the intersexual difference in display maxima to a factor of two. There was no intersexual difference in display minima. Beetles were demonstrated to be sensitive to differences in both maximum and minimum displays on rewarding male trees, a necessary prerequisite for directional selection on display size. Beetle captures were significantly higher at male trees during floral display maxima, and no intersexual differences in capture rate occurred during floral display minima. However, capture rates at male trees did not decline as predicted, and the pattern of captures was consistent with crepuscular activity. Beetle captures at male and female trees were lower from 1800 to 0600 and 1000 to 1400, and higher from 0600 to 1000 and 1400 to 1800, but the differences were only significant at female trees. These data suggests that foraging errors are numerous, frequent, and the result of overall foraging activity.     

Pollination Ecology and Endemic Adaptation of Pedicularis howellii Gray (Scrophulariaceae)

Abstract Pedicularis howellii , endemic to the Siskiyou Mountains of California-Oregon, is a root hemiparasite obligately dependent upon bumblebee pollinators that remove pollen by vibration from its short-tubed, nectarless, rostrate flowers, which reflect visible and ultraviolet (360nm) light attractive to Bombus foragers. All six Bombus species in the study area pollinated the plant, but only on P. howellii and P. racemosa were B. mixtus workers the most abundant pollinators among the seven bumblebee-pollinated plants studied, including Delphinium decorum, Dodecatheon jeffreyi, Penstemon newberryi, P. shastensis, and Phacelia heterophylla. Analysis of corbicular pollen loads of Bombus pollinators indicated that pollen foragers on Pedicularis species were less pollen-constant than all other bumblebee pollinators. Although P. howellii and P. racemosa blooming periods overlapped slightly, phenological isolation of blooming periods of plants sharing the same pollinators was not evident. Chemical soil analysis of its habitat and quadrat analysis of the population structure of Pedicularis howellii indicated that the plant grows in a moderately fertile forest soil and is restricted to the edge of forest canopy openings where sunlight favors development of plants to the flowering stage. The endemism of P. howellii is related to a similar "edge effect" survival of P. furbishiae in a boreal forest riparian habitat previously studied.     

Dioecy and the evolution of pollination systems inSchiedea and Alsinidendron (Caryophyllaceae:Alsinoideae) in the Hawaiian Islands

The transition from biotic to wind pollination and the consequencesof this transition for the evolution of dioecious breeding systems wereinvestigated in Schiedea and Alsinidendron(Caryophyllaceae: Alsinoideae), genera endemic to the Hawaiian Islands. The potential for wind pollination was studied for five species ofSchiedea using a wind tunnel. Morphological correlates of windpollination for these species were then used to infer the presence orabsence of wind pollination in the remaining Schiedea species. Hermaphroditic Alsinidendron and Schiedea species,which occur in mesic to wet forests, or less commonly in dry habitats,show little or no indication of wind pollination. These species had lowpollen:ovule ratios, large relative pollen size, diffuse inflorescences,substantial nectar production in several cases, and appear to bebiotically pollinated or autogamous. Sexually dimorphic species, whichall occur in dry habitats, are wind pollinated, based on wind tunnelresults or morphological adaptations indicating the potential for windpollination. These adaptations include high pollen:ovule ratios, smallpollen size, moderately to highly condensed inflorescences, and reducednectaries and nectar production. Shifts to wind pollination anddimorphism are strongly correlated in Schiedea, suggesting theclose functional relationship of the twophenomena.     

华凤仙花部特征和传粉系统研究

研究了华凤仙（Impatiens chinensis L.）的花部特征和传粉系统,结果表明华凤仙单花期为2.3 d,雄性期是雌性期的6.8倍。花蜜量和花蜜可溶性糖含量分别为0.56 μL和28.2%。开花当天柱头即具有可授性,花粉活力在花朵刚开放时最高（95%）,至花朵凋谢之前仍保持较高的活力（55%）。花粉胚珠比（5 730.3±2 941.1）和套袋实验的结果表明华凤仙属于自交亲和但以异交为主的繁育系统,传粉过程需要传粉者。蜜蜂、熊蜂、蝶类和几种芦蜂是华凤仙的主要访花者,最有效的传粉者为三条熊蜂。考氏无垫蜂作为盗蜜者,可能是除正常访花者之外,对华凤仙的有性繁殖影响最大的生物因素。