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At least 631 records · Page 35Linked to original sources
PubMed1999

Population differences in self-fertility in the "self-incompatible" milkweed Asclepias exaltata (Asclepiadaceae).

Individual plants of Asclepias exaltata (Asclepiadaceae) typically express an unusual self-incompatibility system under single-gene control. Hand-pollinations performed in six natural populations detected occasional self-fertile plants. The frequency of self-fertile individuals ranged from 0 to 34.0% and differed significantly among populations. Self-fertility appears to be under genetic control, as the ability of most plants (80.0 %) to set fruit following self-pollinations was identical under natural and greenhouse conditions. Seed- and fruit-set, however, were significantly lower from self- vs. cross-pollinations. Allozyme analysis of the population with the highest frequency of self-fertility revealed that adult plants were not significantly inbred. Finally, fruit-set following within-population cross-pollinations did not differ from that following wide, between-population cross-pollinations.

Journal Article↗
PubMed1999

Stigma behavior in Mimulus aurantiacus (Scrophulariaceae).

The bilobed stigma of many species in the order Scrophulariales closes in response to touch by an animal pollinator. In hummingbird-pollinated bush monkey flower, Mimulus aurantiacus (Scrophulariaceae), closure is rapid, occurring within seconds of tactile stimulus. We investigated the proximate causes of stigma closure and subsequent reopening in M. aurantiacus, as well as potential costs and benefits of stigma closure for female fitness. Stigma closure is elicited by both touch and pollen, but closure in response to pollen is much slower, requiring 0.5-1.5 h. Stigmata reopen within 2.5-4.5 h if touch, but no pollen, is applied. Upon receipt of pollen, most stigmata remain closed for the remaining lifetime of the flower, even if less pollen is received than is needed for full seed set. Those stigmata that do reopen after pollination generally require between 20 and 28 h to do so, much longer than for unpollinated stigmata. Reopening after pollination appears to be a response to low seed set rather than to low pollen load. Natural pollination of stigmata manipulated to prevent closure shows that closure does not increase capture of pollen or seed set. In fact, closure reduces the average pollen load received by flowers. Despite this, there is no evidence that stigma closure has any negative effect on female fitness in terms of seed set or germinability. Hypotheses for the adaptive significance of stigma closure are discussed. Understanding proximate causes of stigma closure and reopening is essential in the evaluation of these hypotheses.

Journal Article↗
PubMed2000

Morphological variation and female reproductive success in two sympatric Trillium species: evidence for phenotypic selection in Trillium erectum and Trillium grandiflorum (Liliaceae).

I investigated the mating systems and phenotypic variation of two sympatric spring ephemerals, Trillium erectum and T. grandiflorum (Liliaceae), and phenotypic selection acting through female reproductive success for 11 morphological characters in five sympatric populations of the two species. I examined the degree of self-compatibility, pollinator-visitation rates, and pollen limitation of fruit and seed production in both species. Both Trillium species were self-compatible, but outcrossed flowers produced more successful fruits and seeds than self-pollinated flowers. Pollinator-visitation rates to the two species were low compared to other insect-pollinated spring ephemerals. In addition, both T. erectum and T. grandiflorum experienced pollen limitation in fruit and/or seed production; however, levels of fecundity in both species may be influenced by resource availability as well. I found significant phenotypic variation in 11 morphological characters within and among the five study populations. The sizes of all morphological characters were positively correlated. In general, larger T. erectum and T. grandiflorum produced more seeds. Phenotypic selection analysis revealed that direct and indirect selection acted on the size of morphological characters for both species. But there was no detectable selection acting on plant shape. This study reveals that variation in plant size exists within and among populations of both species, and this variation is associated with variance in female reproductive success. Spatial and temporal variation in pollinator and/or resource abundance may play a role in the phenotypic variation exhibited by both Trillium species.

Journal Article↗
PubMed2000

Pollen competition in a natural population of Cucurbita foetidissima (Cucurbitaceae).

The pollen competition hypothesis predicts that when the number of pollen grains deposited onto stigmas exceeds the number of ovules, selection can operate in the time frame between deposition and fertilization. Moreover, because of the overlap in gene expression between the two phases of the life cycle, selection on microgametophytes may alter the resulting sporophytic generation. The extent to which pollen competition occurs in nature has been unclear, because tests of the predictions of the pollen competition hypothesis have used cultivars and/or artificial growth conditions and hand-pollination techniques. In this study we used a wild species, Cucurbita foetidissima, in its natural habitat (southern New Mexico) to determine the amount and timing of the arrival of pollen onto stigmas, the relationship between pollen deposition and seed number, and the effects of the intensity of pollen competition on progeny vigor. We found that ∼900 pollen grains are necessary for full seed set and that a single visit by a pollinator results in the deposition of 653.0 ± 101.8 pollen grains. About 29% of the flowers receiving a single pollinator visit had 900 or more pollen grains on its stigma. Moreover, within 2 h of anthesis, >4000 pollen grains were deposited onto a typical stigma, indicating that multiple pollinator visits must have occurred. Fruits produced by multiple visits had greater seed numbers (206 vs. 147) than fruits produced by a single visit. Finally, the progeny produced by multiple pollinator visits were more vigorous than those produced by single visits with respect to five measures of vegetative growth (MANCOVA, Wilks' lambda = 0.96, F(6,370) = 2.54, P < 0.02. These data demonstrate that conditions for pollen competition exist in nature and support the prediction that pollen competition enhances offspring vigor.

Journal Article↗
PubMed2000

Pollen viability reduction as a potential cost of ant association for Acacia constricta (Fabaceae).

Field studies investigating the impact of ants on the reproduction of plants bearing extrafloral nectaries have traditionally focused on seed production, a component of female fitness. The purpose of this study was to test whether ants can affect the pollen viability, a component of male fitness, when they visit flowers of the shrub Acacia constricta. Acacia constricta inflorescences hand-pollinated with flowers over which Formica perpilosa ants had crawled set significantly fewer seed pods than inflorescences hand-pollinated by control flowers that had no contact with ants. Many ant species secrete antibiotic substances onto the integument that render pollen inviable, and these secretions are probably the mechanism for reduced pollen viability in this study. The ratio of seed pods produced by self-pollinated inflorescences to those produced by cross-pollinated inflorescences was 0.16, indicating that A. constricta is largely self-incompatible. Because F. perpilosa workers forage primarily on the acacia tree under which they nest, they are unlikely to serve as efficient vectors of outcrossing. Previous work showed that A. constricta shrubs with F. perpilosa ants produce approximately twice as many seeds as similarly sized plants not so associated. The results indicate that association with F. perpilosa could cause a reproductive trade-off for A. constricta: benefits to female function may be accompanied by costs to male function. Selection to discourage ant visitation to flowers may have affected the pollination biology of this and other ant-associated plant species.

Journal Article↗
PubMed2000

Pollen quality limits seed set in Burchardia umbellata (Colchicaceae).

In self-incompatible plants, interference by self pollen or genetically related pollen can potentially exacerbate pollen limitation, although this has rarely been demonstrated. We examined the breeding system, pollen limitation, and pollen interference using self- and cross- pollinations and pollen supplementations in Burchardia umbellata, an insect-pollinated lilioid monocot. Ovule fertilization and seed set were less following selfing than crossing (22 vs. 78% and 4 vs. 73%, respectively), indicating partial self-incompatibility. Flowers were partially protandrous, and flowers opened concurrently on plants potentially allowing self pollen interference. Natural seed set was pollen limited and varied within and among years, probably due to variation in flowering plant density. Interference by self or genetically related pollen caused pollen limitation as evidenced by increased seed set of bagged cross-pollinated plants compared to unbagged pollen-supplemented plants in two years. In 1996, both fertilization and seed set increased in response to cross-pollination, indicating that interference occurred in the style and ovary. In 1997, only seed set increased after cross-pollination indicating that interference occurred in the ovary. Inappropriate pollen deposition may contribute to pollen limitation more often than previously recognized and should select for floral traits that decrease deposition of self or related pollen.

Journal Article↗
PubMed2003

Effects of floral display and plant abundance on fruit production of Ryncholaelia glauca (Orchidaceae).

Flowering plant density can increase number of visits and fruit set in multi-flowering plants, however this aspect has not been studied on few flower species. We studied the effects of individual floral display and plant density on the fruit production of the epiphytic, moth-pollinated orchid, Ryncholaelia glauca, in an oak forest of Chavarrillo, Veracruz, Mexico. Species is non-autogamous, and produced one flower per flowering shoot each flowering season. We hypothesized that orchids with more flowering shoots and those on trees with clumps of conspecific should develop more fruits than isolated ones. R. glauca population flowers synchronouly, and individual flowers last up to 18 days, with flowers closing rapidly after pollination. Individuals produced few flowers per year, although some plants developed flowers in both seasons and fewer of them developed fruits both years. There was no relationship between flower number per orchid, or per host tree, with the number of fruits developed per plant. Host trees with flowering and fruiting orchids were randomly dispersed and the pattern of distribution of flowering and fruiting plants was not related. Apparently, pollinators visit the flowers randomly, with no evidence of density dependence. The fruit set of R. glauca was as low as fruit set of multi-flowered orchids moth pollinated, suggesting that fruit set on moth pollinated orchids could be independent of the number of flowers displayed.

Flowers↗
PubMed2003

[Floral biology, reproductive system and reproductive success of Macroptilium fraternum (Fabaceae)].

Observations about the floral biology and the reproductive system of Macroptilium fraternum were made in two populations in Argentina, with different edaphic conditions, situated at the southern area of distribution of the species. The coexistence of two kind of flowers in the same plant was detected in both populations and in herbarium material from other localities: a) cleistogamous preanthesis flowers and b) pseudocleistogamous flowers. The cleistogamous preanthesis flowers possessed wings longer than 5 mm and were disposed in pubescent, erect, racemes exposed above the level of the foliage. The anthesis lasted approximately 5 hours on sunny days or 9 hours on rainy days, the right wing covered the left wing, the corolla acquired a bilabiate aspect, offering the left wing as landing platform; they produced a low quantity of nectar (0.18 +/- 0.13 microliter); they did not receive pollinator visits; approximately four hours after the beginning of the anthesis on sunny days the ovary started to grow; in the bud, the receptive stigma was covered with germinating pollen grains from the same floral unit. The pseudocleistogamous flowers possessed wings shorter than 5 mm that were disposed in brief, hirsute and prostrate racemes, non subterranean as in other Macroptilium species; the banner started to spread exposing partially the wings, the left wing limb surrounded the keel and never spread; the right wing started to spread and after 2 seconds refolded and began to wither, the ovary began to grow immediately; the flower did not offer a surface to allow visitors to settle; in the buds the stigma was receptive and found with pollen grains from the same floral unit emitting their tubes. The relative reproductive success was low (natural pollination = 8%; spontaneous self-pollination = 3%), probably due to the low pollen viability, the high percentage of seed abortion and the lack of pollinator's visits. The production of both flower types is not conditioned by edaphic factors, as they were found in plants belonging to different environments. Study of the progeny of both floral types in both populations has demonstrated that each one produces a similar amount of seeds contributing to the next generation with plants of similar characteristics (slow development, low resistance to infections and high mortality). The absence of pollinators in these flowers (in part because they preferred to visit flowers of other species with more reward and in part because of the fragmentation of the habitats), would be producing inbreeding depression in the studied populations; if the germplasm variability is not preserved, these populations situated at the Southern end of the distribution range of the species could become extinguished.

Fabaceae↗
PubMedDate not supplied

[Polymorphism of Phaseolus vulgaris var. aborigineus (fabaceae). Evidences of natural hibridation].

A polymorphic population of Phaseolus vulgaris var. aborigineus growing at the Northwest of Argentina was studied. In order to know the origin of this polymorphism, some plants belonging to the var. aborigineus, other plants showing floral dimorphism and other individuals with particular characters were collected. Their seeds, obtained after field-work treatments of autogamy and free pollination, were sown in a greenhouse, isolated of the access of pollinators. The growth of each plant was followed until its fructification, and the number of plants that died due to infections was recorded. The number of plants that flowered and fructified was registered in order to study their reproductive success. The floral, fruit and seed qualitative and quantitative characters were documented. With the results obtained, the authors concluded that those individuals that showed floral dimorphism are probably a result of hybridization and introgression between the var. aborigineus and "old cultivars". This hypothesis is supported by the presence of divergent segregation, observed in the offspring of the plants with this segregation. Other crops should allow the genic flow between the parental entities, with the consequence of the establishment of an hybrid population coexistent with their ancestors. Perhaps, as a result of introgression, the stabilized lines exhibit characters different from their parental varieties. The results of autopollination and free pollination in those individuals assigned to var. aborigineus, showed that free pollination brings a great genetic plasticity, because next generations can persist and resist infections. The offspring of the F1 was followed. The plants that belonged to var. aborigineus, product of free pollination, exhibited fast growth and were healthy, while the descendant of the individuals with the floral dimorphism showed characteristics that allowed to conclude the possible existence of degeneration of the hybrid progeny; this characteristics were: curled radicles with cotyledons that never emerge, plantule's apex that soon die with the following development of branches from the cotyledon's axil, and death after some weeks. This degeneration indicates that an unwanted gene flow in the area could lead to a decline in the wild bean population. The vigor, high reproductive success and resistance to illnesses of the individuals corresponding to the var. vulgaris, whose progenitor was treated for free fecundation, and the offspring of the plants with cultivated characteristics, are indicative of the necessity of preserving this germplasm to evaluate its agronomic potential to brief term. The DNA analyses already initiated, will allow the confirmation of the hypotheses outlined in this work.

Argentina↗
PubMed2005

[The results of exercise challenge in patients with seasonal allergic rhinitis].

BACKGROUND: Allergic rhinitis is considered a risk factor for the future development of bronchial asthma. It therefore seems essential to identify patients who are threatened with this disease and in whom no disturbing bronchial symptoms have already occurred. The aim of this study was to evaluate the incidence of nonspecific bronchial hyperactivity based upon exercise results of patients with pollinosis. INVESTIGATED GROUP: The study encompassed 27 patients with seasonal allergic rhinitis allergic to tree pollens, but without symptoms of asthma. Exercise provocation test were performed in patients in the period before, during and after completion of the pollination period. Additionally, during the pollination period sIgE and nasal eosinophilia were determined. The control group was composed of 12 patients allergic to Artemisia pollen. RESULTS: In the study group, a pathological result of provocation test was obtained in 1 patient (3.7%) before the pollination period, in 7 patients (25.9%) during and in 4 patients (14.8%) after completion of the pollination period. Subjects with positive test result had higher levels of nasal eosinophilia, while there was no relation between its result and sIgE levels. Only one case of positive exercise challenge was identified among desensitized patients. CONCLUSIONS: During the pollination period nonspecific bronchial hyperreactivity develops in some patients with seasonal allergic rhinitis; it can be sustained for some time after disappearance of pollens from the atmosphere and can be identified using an exercise challenge. Incidence of bronchial hyperreactivity in desensitized patients was lower than in those subjected to symptomatic treatment.

Adult↗
PubMed2006

A novel role for proline in plant floral nectars.

Plants offer metabolically rich floral nectar to attract visiting pollinators. The composition of nectar includes not only sugars, but also amino acids. We have examined the amino acid content of the nectar of ornamental tobacco and found that it is extremely rich (2 mM) in proline. Because insect pollinators preferentially utilize proline during the initial phases of insect flight and can reportedly taste proline, we determined whether honeybees showed a preference for synthetic nectars rich in proline. We therefore established an insect preference test and found that honeybees indeed prefer nectars rich in the amino acid proline. To determine whether this was a general phenomenon, we also examined the nectars of two insect-pollinated wild perennial species of soybean. These species also showed high levels of proline in their nectars demonstrating that plants often produce proline-rich floral nectar. Because insects such as honeybees prefer proline-rich nectars, we hypothesize that some plants offer proline-rich nectars as a mechanism to attract visiting pollinators.

Amino Acids↗
PubMed2005

Multicomponent floral signals elicit selective foraging in bumblebees.

Flower constancy, or the tendency of individual pollinators to visit sequentially a single flower type even when other equally rewarding types are available, has important implications for animal-pollinated plants. Yet, the proximal reason for the behaviour still remains poorly understood. Here I show that bumblebees visiting equally rewarding flowers that differ in size and odour are more flower constant and less efficient (visited fewer flowers per minute) than bees visiting flowers that differ in size only and odour only. These results are consistent with the view that flower constancy in pollinators is related to their inability to perceive, process or recall multicomponent floral signals. I discuss these findings in the context of pollinator behavioural mechanisms and the evolution of floral diversity.

Animals↗
PubMed2003

Gene flow estimation with microsatellites in a Malagasy seed orchard of Eucalyptus grandis.

Eucalyptus grandis has a mixed-mating reproductive system. Malagasy Eucalyptus seed orchards were established 15 years ago with two aims both based on panmixia: open-pollinated seed production and genetic improvement. The panmixia hypothesis has never been confirmed in the seed orchard. From a seedling seed-orchard stand comprising 349 trees and using data obtained with six selected microsatellite markers, paternity analysis was performed for 724 offspring collected on 30 adult trees. Paternity assignment, based on exclusion procedures and likelihood-ratio method, was achieved with high accuracy; the exclusion probability value was 0.997. The outcrossing rate was very high (96.7%). More than 50% of potential male trees (199 out of 349) in the seed orchard contributed to pollination for 440 offspring of 30 progenies (8.6% of the basic population). The pollination rate from outside the seed orchard was high (39.2%), but might be due to the small size of this seed orchard. This study showed that "panmixia-like pollination" can be assumed.

Crosses, Genetic↗
PubMed2003

Gene flow among different taxonomic units: evidence from nuclear and cytoplasmic markers in Cedrus plantation forests.

Hybridization and introgression are important natural evolutionary processes that can be successfully investigated using molecular markers and open- and controlled-pollinated progeny. In this study, we collected open-pollinated seeds from Cedrus atlantica, Cedrus libani and C. libani x C. atlantica hybrids from three French-plantation forests. We also used pollen from C. libani and Cedrus brevifolia to pollinate C. atlantica trees. The progeny were analyzed using three different types of molecular markers: RAPDs, AFLPs and cpSSRs. Chloroplast DNA was found to be paternally inherited in Cedrus from the progeny of controlled-crosses. Heteroplasmy, although possible, could not be undoubtedly detected. There was no indication of strong reproductive isolating barriers among the three Mediterranean Cedrus taxa. Gene flow between C. atlantica and C. libani accounted for 67 to 81% of viable open-pollinated seedlings in two plantation forests. We propose that Mediterranean Cedrus taxa should be considered as units of a single collective species comprising two regional groups, North Africa and the Middle East. We recommend the use of cpSSRs for monitoring gene flow between taxa in plantation forests, especially in areas where garden specimens of one species are planted in the vicinity of selected seed-stands and gene-conservation reserves of another species.

Cedrus↗
PubMed2005

Paternity analysis using microsatellite markers to identify pollen donors in an olive grove.

Olive (Olea europaea L.) is a wind-pollinated, allogamous species that is generally not considered to be self-compatible. In addition, cross-incompatibilities exist between cultivars that can result in low fruit set if compatible pollinisers are not planted nearby. In this study, microsatellite markers were used to identify 17 genotypes that were potential pollen donors in a commercial olive orchard. DNA typing with the same primers was also applied to 800 olive embryos collected from five cultivars in the grove over 2 years of study. Pollen donors for the cultivars Barnea, Corregiola, Kalamata, Koroneiki, and Mission were estimated by paternity analysis, based on the parental contribution of alleles in the genotypes of the embryos. The exclusion probability for the marker set was 0.998 and paternity was assigned on the basis of the 'most likely method'. Different pollen donors were identified for each of the maternal cultivars indicating that cross-compatibilities and incompatibilities varied between the genotypes studied. Cross-pollination was the principal method of fertilization, as selfing was only observed in two of the embryos studied and both of these were from the cultivar Mission. This is the first report where these techniques have been applied to survey the pollination patterns in an olive grove. The results indicate that careful planning in orchard design is required for efficient pollination between olive cultivars.

Agriculture↗
PubMed2000

Sulphur-containing "perfumes" attract flower-visiting bats.

We tested the attractiveness of individual scent compounds of bat-pollinated flowers to their pollinators, small flower-visiting bats of the genus Glossophaga (Phyllostomidae). Twenty compounds belonging to four different chemical substance classes were tested, both in the laboratory and in the field. In the laboratory, the bats (Glossophaga soricina) approached odour sources spontaneously and without preceding experience. Without ever receiving any reward they preferred the scent of a sulphur-containing compound, dimethyl disulphide, to several other odour components emitted by bat-pollinated flowers, and to scentless controls. In the field, at La Selva station in the tropical lowland rain forest of Costa Rica, G. commissarisi were attracted by two sulphur-containing compounds, dimethyl disulphide and 2,4-dithiapentane, to visit artificial flowers filled with sugar water. Thus, in nectarivorous bats the sense of smell obviously plays an important role in searching for and localising food sources, and even single components of the scent bouquets of bat-pollinated flowers are attractive. The preference for sulphur-containing odours seems to be innate.

Animals↗
PubMed2001

Ethylene response to pollen tube growth in Nicotiana tabacum flowers.

In flowers of Nicotiana tabacum L., pollination induces a transient increase in ethylene production by the pistil. The characteristic dynamics of the increase in ethylene correspond to the main steps of the pollen-tube journey into the pistil: penetration into the stigma, growth through the style, entry into the ovary and fertilization. Ethylene is synthesized de novo in the pistil, and its production is reduced in the dark. Ethylene production was monitored in tobacco flowers after pollination with incongruous pollen from three different Nicotiana species, N. rustica, N. repanda and N. trigonophylla, and with pollen from Petunia hybrida. Pollen from all of these different sources can germinate on the stigma surface but each pollen type shows a different behavior and efficiency in penetrating the pistil tissues. Thus, these different crosses provided a model with which to study the response of the pistil to pollination and fertilization. Ethylene evolution upon pollination in tobacco differed in each cross, suggesting that ethylene is correlated with the response to pollen tube growth in the tobacco flower.

Amino Acids, Cyclic↗
PubMed2003

Pollen flow in the distylous Palicourea fendleri (Rubiaceae): an experimental test of the Disassortative Pollen Flow Hypothesis.

The Disassortative Pollen Flow Hypothesis proposed by Darwin postulates that the relative position of anthers and stigmas in distylous flowers enhances pollen flow between flowers of different morphs (legitimate pollination), in comparison to flow between flowers of the same morph (illegitimate pollination). In order to test this hypothesis, we measured pollen transport, mediated by a trained Copper-rumped Hummingbird (Amazilia tobaci), between flowers of the distylous Palicourea fendleri under laboratory conditions. In individual tests, we offered to the hummingbird a pollen donor flower and two emasculated recipient flowers in a controlled sequence. After each foraging bout, we counted the number of pollen grains transported from the donor flower to the stigmas of both recipient flowers. In agreement with Darwin's hypothesis, we found that hummingbirds transport pollen of "pin" flowers in significantly higher numbers to legitimate "thrum" stigmas, even if previously visiting a "pin" flower. However, "thrum" pollen was deposited in greater numbers on illegitimate "thrum" stigmas. We interpret this asymmetry largely as the consequence of floral morphology; pollen flow was greater between anthers and stigmas that exhibit greater spatial matching. In P. fendleri, the position of floral organs along the corolla tube does not always precisely correspond. In our experimental system, the probability that the pollinator extracts a pollen grain from the anther and the probability of self-pollination were both dependent on the type of floral morph. We discuss the relevance of the latter findings in relation to other studies of pollen flow in heterostylous species.

Animals↗