巴旦杏授粉试验及花粉管生长的荧光显微观察

对巴旦杏4个主栽品种的授粉试验结果表明：自花授粉试验中“鹰嘴”、“双果”坐果率分别为19．74％和4．29％,“纸皮”和“麻壳”坐果率为零;自然授粉状态下4个主栽品种坐果率在9．37％－20．13％之间;人工异花授粉试验中4个品种9个授粉组合坐果率绝大多数都在40％以上,其中混合花粉授粉试验结果最好;人工养蜂条件下的坐果率明显高于无蜂自然授粉的坐果率,昆虫传粉可达到人工混合花粉授粉的效果。授粉试验还表现出巴旦杏雌蕊柱头的有效授粉时间为开花后花期的前4d,授粉越早,越有利于坐果。荧光显微观察表明,巴旦杏花粉管最早约于授粉第7天通过花柱基部到达子房室,第8天前后到达胚珠。     

Effects of sequential pollination on the success of "fast" and "slow" pollen donors in Hibiscus moscheutos (Malvaceae)

Competition among pollen grains for the chance to fertilize ovules typically involves two stages: arrival times on stigmas and/or the growth of pollen tubes through styles. In a previous study of Hibiscus moscheutos, we found that individual pollen donors often differed in pollen tube competitive ability. Here we determined whether short delays in pollen arrival time altered the average success of "fast" and "slow" pollen donors when both types of pollen experienced the same delays. Hand-pollination experiments were carried out using four pairs of pollen donors that differed in competitive ability. We allowed delays of 15 or 30 min between the first and second pollen donor and then determined seed paternity using allozyme markers. The second donor typically sired fewer seeds than pollen that arrived earlier, but, contrary to expectation, "faster" pollen did not always sire significantly more seeds than "slower" pollen when each was applied after delays of the same duration. In two of the four pairs of donors, differences that were seen following simultaneous pollinations disappeared when each type of pollen was applied following identical delays of 15 or 30 min. This unexpected response suggests that the dynamics of pollen tube competition are more complex than anticipated.     

Beyond pollen:ovule ratios: Evolutionary consequences of pollinator dependence and pollination efficiency for pollen and ovule production in angiosperms

Premise

The relative per-flower production of ovules and pollen varies broadly with angiosperm mating systems, with outcrossing types commonly producing more pollen grains per ovule than selfing types. The evolutionary causes of this variation are contentious, especially the relevance of pollination risk. Resolution of this debate may have been hampered by its focus on pollen:ovule (P:O) ratios rather than on the evolution of pollen and ovule numbers per se.

Methods

Using published mean ovule and pollen counts, we analyzed associations with the proportion of removed pollen that reaches stigmas (pollen-transfer efficiency) and differences between pollinator-dependent and autogamous forms within and among species. Analyses involved Bayesian methods that simultaneously considered variation in pollen and ovule numbers and accounted for phylogenetic relatedness. We also assessed the utility of P:O ratios as mating-system proxies and their association with female outcrossing rates.

Results

Median pollen number declined consistently with pollen-transfer efficiency among species, whereas median ovule number did not. Similarly, in both intraspecific and interspecific analyses, pollinator-dependent plants produced more pollen than autogamous plants, whereas ovule production did not differ statistically. Distributions of P:O ratios overlapped extensively for self-incompatible and self-compatible species and for different mating-system classes, and P:O ratios correlated weakly with outcrossing rate.

Conclusions

Our findings demonstrate that pollinator dependence and pollination efficiency commonly influence the evolution of pollen number per flower but have more limited effects on ovule number. P:O ratios provide ambiguous, possibly misleading, information about mating systems, especially when compared among clades.

     

Ecological context of the evolution of self-pollination in Clarkia xantiana: population size, plant communities, and reproductive assurance

The repeated evolutionary transition from outcrossing to self-pollination in flowering plants has been suggested to occur because selfing provides reproductive assurance. Reports from biogeographical and ecological surveys indicate that selfing taxa are often associated with stressful and ephemeral environments, situations in which plant abundance is low (e.g., Baker's law) and with novel plant communities, however experimental tests of ecological hypotheses are few. In this study, we examined the ecological context of selection on mating system traits (herkogamy and protandry) in a California annual, Clarkia xantiana, where natural selfing populations differ from outcrossing populations in that they are often of small size or low density and occur mainly outside the range of pollinator-sharing congeners. We constructed artificial populations of plants with broad genetic variation in floral traits and manipulated two ecological factors, plant population size, and the presence versus absence of pollinator-sharing congeners, in the center of the geographic range of outcrossing populations. We found evidence for context-dependent selection on herkogamy and protandry via female fitness in which reduced traits, which promote autonomous selfing, were favored in small populations isolated from congeners whereas selection was comparatively weak in large populations or when congeners were present. In small, isolated populations, the fertility of plants with low herkogamy or protandry was elevated by 66% and 58%, respectively, compared to those with high herkogamy or protandry. The presence of pollinator-sharing congeners augmented bee visitation rates to C. xantiana flowers by 47% for all bees and by 93% for pollen specialists. By facilitating pollinator visitation, congeners mitigated selection on mating system traits in small populations, where outcross mating success is often low (the Allee effect). We also found support for the hypothesis that pollinator availability directly influenced variation in the strength of selection on herkogamy among populations. The striking parallels between our experimental results and patterns of variation in ecological factors across the geographic range of outcrossing and selfing populations suggest that reproductive assurance may play a central role in directing mating system evolution in C. xantiana.     

Viability of cotton and canola pollen on the proboscis of Helicoverpa armigera: implications for spread of transgenes and pollination ecology

Abstract.  1. Pollen can be transported thousands of kilometres by insects but its viability after long-distance transport is not known. Knowing the potential for this mechanism to cause outcrossing of transgenes from genetically modified (GM) plants is important for risk assessments.
2. The viability of pollen from cotton ( Gossypium hirsutum L.) and canola ( Brassica napus L.) was determined after placing it on the proboscis of Helicoverpa armigera moths for intervals of up to 32 h. Viability of both cotton and canola pollen declined at a much greater rate when in contact with the moth proboscis. Most was non-viable by 8 h compared with 16 h for control cotton pollen or 32 h for canola pollen.
3. There was no significant difference in the rate of decline of pollen viability between the five conventional cotton varieties, or between these and the one GM cotton variety used in these experiments.
4. The number of canola pollen grains remaining on the proboscis declined over time. Very few cotton pollen grains were retained on the proboscis.
5. The reduction in pollen viability during contact with the proboscis might indicate partial ingestion of the pollen via the proboscis.
6. The points above suggest that pollen is unlikely to remain attached or remain viable when carried over large distances by H. armigera . The implications for spread of pollen from transgenic plants and for pollination ecology in general are discussed.     

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.     

Hydrophilous pollination and breeding system evolution in seagrasses: a phylogenetic approach to the evolutionary ecology of the Cymodoceaceae

COX, P. A. & HUMPHRIES, C. J. 1992. Hydrophilous pollination and breeding system evolution in seagrasses: a phylogenetic approach to the evolutionary ecology of the Cymodoceaceae. A phylogenetic analysis of seagrasses of the Cymodoceaceae shows the Cymodoceaceae to be monophyletic and Posidoniaceae to be their sister group. Information on the pollination ecologies and breeding systems of the various genera of the Cymodoceaceae were plotted onto the consensus tree obtained for the group. From this analysis, it is suggested that the clade composed of the Zosteraceae, Posidoniaceae and Cymodoceaceae evolved from a freshwater hydrophilous ancestor that developed submarine pollination and filiform pollen in association with invasion of the marine environment. Dioecism and surface pollination appear to have evolved in the progenitor of the Cymodoceaceae, and hence the seagrasses of the Cymodoceaceae are dioecious due to common descent rather than to convergent evolutionary processes in extant genera.     

Beyond the pollination syndrome: nectar ecology and the role of diurnal and nocturnal pollinators in the reproductive success of Inga sessilis (Fabaceae)

Inga species present brush‐type flower morphology allowing them to be visited by distinct groups of pollinators. Nectar features in relation to the main pollinators have seldom been studied in this genus. To test the hypothesis of floral adaptation to both diurnal and nocturnal pollinators, we studied the pollination ecology of Inga sessilis, with emphasis on the nectar secretion patterns, effects of sequential removals on nectar production, sugar composition and the role of diurnal and nocturnal pollinators in its reproductive success. Inga sessilis is self‐incompatible and pollinated by hummingbirds, hawkmoths and bats. Fruit set under natural conditions is very low despite the fact that most stigmas receive polyads with sufficient pollen to fertilise all ovules in a flower. Nectar secretion starts in the bud stage and flowers continually secreting nectar for a period of 8 h. Flowers actively reabsorbed the nectar a few hours before senescence. Sugar production increased after nectar removal, especially when flowers were drained during the night. Nectar sugar composition changed over flower life span, from sucrose‐dominant (just after flower opening, when hummingbirds were the main visitors) to hexose‐rich (throughout the night, when bats and hawkmoths were the main visitors). Diurnal pollinators contributed less than nocturnal ones to fruit production, but the former were more constant and reliable visitors through time. Our results indicate I. sessilis has floral adaptations, beyond the morphology, that encompass both diurnal and nocturnal pollinator requirements, suggesting a complementary and mixed pollination system.     

The biomechanics of pollen release: new perspectives on the evolution of wind pollination in angiosperms

Evolutionary transitions from animal to wind pollination have occurred repeatedly during the history of the angiosperms, but the selective mechanisms remain elusive. Here, we propose that knowledge of pollen release biomechanics is critical for understanding the ecological and evolutionary processes underpinning this shift in pollination mode. Pollen release is the critical first stage of wind pollination (anemophily) and stamen properties are therefore likely to be under strong selection early in the transition. We describe current understanding of pollen release biomechanics to provide insights on the phenotypic and ecological drivers of wind pollination. Pollen release occurs when detachment forces dominate resistive forces retaining pollen within anthers. Detachment forces can be active or passive depending on whether they require energy input from the environment. Passive release is more widespread in anemophilous species and involves processes driven by steady or unsteady aerodynamic forces or turbulence-induced vibrations that shake pollen from anthers. We review empirical and theoretical studies suggesting that stamen vibration is likely to be a key mechanism of pollen release. The vibration response is governed by morphological and biomechanical properties of stamens, which may undergo divergent selection in the presence or absence of pollinators. Resistive forces have rarely been investigated for pollen within anthers, but are probably sensitive to environmental conditions and depend on flower age, varying systematically between animal- and wind-pollinated species. Animal and wind pollination are traditionally viewed as dichotomous alternatives because they are usually associated with strikingly different pollination syndromes. But this perspective has diverted attention from subtler, continuously varying traits which mediate the fluid dynamic process of pollen release. Reinterpreting the flower as a biomechanical entity that responds to fluctuating environmental forces may provide a promising way forward. We conclude by identifying several profitable areas for future research to obtain deeper insight into the evolution of wind pollination.     

Pollen and resource limitations to lifetime seed production in a wild population of the endangered plant Disanthus cercidifollus var.Iongipes H.T.Chang (Hamamelidaceae)

Disanthus cercidifolius Maxim.var.longipes H.T.Chang,a plant species that only occurs in a few counties in Hunan,Jiangxi and Zhejiang Provinces and with a relatively small number of individuals,is ranked as a second Class endangered species for conservation in China.We have studied the effect of pollen and resources available to female reproduction,and the reproductive mechanism of "excess flowers with low fruit set" in Disanthus cercidifolius Maxim.var.longipes H.T.Chang was discussed.Results are as follows:Pollen from different sources has significant effects on fruit set and seed set of Disanthus cercidifolius Maxim.var.longipes H.T.Chang.The pollen source rather than pollen numbers significantly affected reproduction of this species.In wild populations,producing one fruit needs about 54.8 flowers,and one satiation seed needs about 6.60 flowers or 83.19 ovules.After fertilizing,which was propitious to flower development,the abortion rate of flower buds was decreasing,but the flowering rate was increasing.The fruit set and seed set was also significantly increasing,while abortion rate of fruit was significantly decreasing.With the increasing percentages of cutting leaves,the fruit set decreased,but the abortion rate of fruit shows no significant differentiation among treatments.After cutting branches that were puny,broken and insectinfested branches,the flower number seemed to be decreasing,but the fruit set and seed set all increased significantly.After removing some flowers,the fruit set was calculated with respect to the number of flowers remaining after the treatment increased with increasing of percentages of flower removal,whereas fruit set calculated with respect to the initial number of flowers remained constant,and the mean weights of per fi'uit and per seed all decreased significantly.Sufficient spatial or temporal heterogeneities in nutrient levels might allow limitation of seed set by resources and pollen in a natural population,while supplying resources may indirectly affect pollination by increasing attraction of the flowers to pollinators.There were very low fruit and seed sets in natural populations ofDisanthus cercidifolius Maxim.var.longipes H.T.Chang.Different factors may have interacted to effect a low fruit set.A joint adoption of the "selection abortion hypothesis","ovary reserve hypothesis" and "male function hypothesis" seems to be the most likely explanation for the reproductive strategy of"excess flowers with few fruit sets" in Disanthus cercidifolius Maxim.var.longipes H.T.Chang.     

The study of plant growth: A link between the physiological ecology and population biology of plants

As the fields of plant physiological ecology and plant population biology mature, it becomes apparent that answers to many key ecological questions require the approaches of both subdisciplines. Historically, the two approaches have developed along separate lines and the links between them have not been clearly defined. In the present paper, we suggest that the study of plant growth may provide one necessary link. This suggestion is motivated by recent trends toward evaluation of physiological responses in terms of growth, and the use of plant size as a predictor of life history traits. In the future, studies which combine these techniques will accrue two important advantages: (1) the significance of plant adaptations (physiological or morphological) may be understood in demographic or Darwinian terms of survivorship and fecundity schedules of the individuals possessing them, and conversely, (2) variation in survivorship and fecundity may be attributed to alternative plant adaptations.     

Reproductive biology and pollination ecology of Triplaris gardneriana (Polygonaceae): a case of ambophily in the Brazilian Chaco

• Triplaris gardneriana (Polygonaceae) is a dioecious pioneer tree reported as insect‐pollinated, despite possessing traits related to anemophily. Here, we analyse the possible roles of insects and wind on the pollination of this species to establish whether the species is ambophilous.
• We carried out observations of floral biology, as well as on the frequency and behaviour of pollinators visiting flowers in a population of T. gardneriana in the Chaco vegetation of Brazil. We conducted experimental pollinations to determine the maternal fertility of female plants and whether they were pollen‐limited, and we also conducted aerobiological experiments to provide evidence of how environmental factors influence atmospheric pollen dispersal.
• The population comprised an area of approximately 152.000 m² and was composed of 603 female and 426 male plants (sex ratio = 0.59:0.41). We observed 48 species of insects visiting flowers of T. gardneriana, of which the bees Scaptotrigona depilis and Apis mellifera scutellata were the most effective pollinators. We recorded pollen grains dispersed by wind on 74% of the glass slides placed on females, located at different distances (1–10 m) from male plants.
• Airborne pollen concentration was negatively correlated with relative humidity and positively correlated with temperature. Our observations and experimental results provide the first evidence that T. gardneriana is an ambophilous species, with pollen dispersal resulting from both animal and wind pollination. This mixed pollination strategy may be adaptive in T. gardneriana providing reproductive assurance during colonisation of sites with different biotic and abiotic conditions.

     

The anatomy of the stigma and style from Cyclamen persicum (Mill.) cv. "pure white" and its relation to pollination success

Old flowers of Cyclamen generate few or no seeds. To understand the pollination problems of Cyclamen we investigate the general anatomy of the stigma and the style of Cyclamen persicum by scanning electron microscopy at different stages of floral maturity. Our investigations confirm that there is a hollow style. Against data commonly found in the literature, we present evidence of pollen germination and tube growth that show the stigma is not outside the style but inside it. Furthermore the maturation process of the style during the flowering time indicates a mechanism by which the stigma becomes shut off through closure at the terminal aperture of the style. At 3 to 5 days after anthesis there was the beginning closure of the style which was nearly completed at 21 days. The substance which leads to the closure is still unknown. The closure of the hollow style is a probable cause for failure of seed set in flowers not pollinated early in anthesis.     

The post-pollination ethylene burst and the continuation of floral advertisement are harbingers of non-random mate selection in Nicotiana attenuata

The self-compatible plant Nicotiana attenuata grows in genetically diverse populations after fires, and produces flowers that remain open for 3 days and are visited by assorted pollinators. To determine whether and when post-pollination non-random mate selection occurs among self and non-self pollen, seed paternity and semi-in vivo pollen tube growth were determined in controlled single/mixed pollinations. Despite all pollen sources being equally proficient in siring seeds in single-genotype pollinations, self pollen was consistently selected in mixed pollinations, irrespective of maternal genotype. However, clear patterns of mate discrimination occurred amongst non-self pollen when mixed pollinations were performed soon after corollas open, including selection against hygromycin B resistance (transformation selectable marker) in wild-type styles and for it in transformed styles. However, mate choice among pollen genotypes was completely shut down in plants transformed to be unable to produce (irACO) or perceive (ETR1) ethylene. The post-pollination ethylene burst, which originates primarily from the stigma and upper style, was strongly correlated with mate selection in single and mixed hand-pollinations using eight pollen donors in two maternal ecotypes. The post-pollination ethylene burst was also negatively correlated with the continuation of emission of benzylacetone, the most abundant pollinator-attracting corolla-derived floral volatile. We conclude that ethylene signaling plays a pivotal role in mate choice, and the post-pollination ethylene burst and the termination of benzylacetone release are accurate predictors, both qualitatively and quantitatively, of pre-zygotic mate selection and seed paternity.     

Pollen competition between morphs in a pollen‐color dimorphic herb and the loss of phenotypic polymorphism within populations

Flower color polymorphism is relatively uncommon in natural flowering plants, suggesting that maintenance of different color morphs within populations is difficult. To address the selective mechanisms shaping pollen‐color dimorphism, pollinator preferences and reproductive performance were studied over three years in Epimedium pubescens in which some populations had plants with either green or yellow pollen (and anthers). Visitation rate and pollen removal and receipt by the bee pollinator (Andrena emeishanica) did not differ between the two color morphs. Compared to the green morph, siring success of the yellow morph's pollen was lower, but that of mixtures of pollen from green and yellow morphs was lowest. This difference, corresponding to in vivo and ex vivo experiments on pollen performance, indicated that pollen germination, rather than tube growth, of the green morph was higher than that of the yellow morph and was seriously constrained in both morphs if a pollen competitor was present. A rare green morph may invade a yellow‐morph population, but the coexistence of pollen color variants is complicated by the reduced siring success of mixed pollinations. Potential pollen competition between morphs may have discouraged the maintenance of multiple phenotypes within populations, a cryptic mechanism of competitive exclusion.     

Effects of patch size and density on flower visitation and seed set of wild plants: a pan-European approach

1.  Habitat fragmentation can affect pollinator and plant population structure in terms of species composition, abundance, area covered and density of flowering plants. This, in turn, may affect pollinator visitation frequency, pollen deposition, seed set and plant fitness.
2.  A reduction in the quantity of flower visits can be coupled with a reduction in the quality of pollination service and hence the plants' overall reproductive success and long-term survival. Understanding the relationship between plant population size and/or isolation and pollination limitation is of fundamental importance for plant conservation.
3.  We examined flower visitation and seed set of 10 different plant species from five European countries to investigate the general effects of plant populations size and density, both within (patch level) and between populations (population level), on seed set and pollination limitation.
4.  We found evidence that the effects of area and density of flowering plant assemblages were generally more pronounced at the patch level than at the population level. We also found that patch and population level together influenced flower visitation and seed set, and the latter increased with increasing patch area and density, but this effect was only apparent in small populations.
5.   Synthesis. By using an extensive pan-European data set on flower visitation and seed set we have identified a general pattern in the interplay between the attractiveness of flowering plant patches for pollinators and density dependence of flower visitation, and also a strong plant species-specific response to habitat fragmentation effects. This can guide efforts to conserve plant–pollinator interactions, ecosystem functioning and plant fitness in fragmented habitats.     

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.