The reproductive biology of a riparian Mediterranean shrub, Nerium oleander L. (Apocynaceae)

This study presents data on the reproductive characteristics of Nerium oleander, an evergreen, sclerophyllous shrub inhabiting the banks of temporary streams in all countries around the Mediterranean seaboard. Two southern Spanish populations (El Garrobo and Grazalema) were selected to investigate flowering, dispersal and seed germination phenologies, together with morphological and functional traits of flowers, fruits and seeds. Observations on pollinator visitation, fruit set, and seedling survival were also carried out. Plants produce massive flower displays of showy, tubular flowers void of nectar that rely on insect cheating for pollination. Hand-pollinations and seed germination tests demonstrated full self-compatibility. Automatic selfing is prevented by spatial separation of stigma and anthers, and pollinators are thus necessary for reproduction. Low pollinator visitation rates are the rule, as indicated by the fact that observations spread over 2 years yielded only eight insect records. Percentage fruit set of open-pollinated flowers was found to be extremely low (0.1–4.9%), while hand-pollination increased fruiting levels to 34–50%. Direct and indirect evidence point to consistently pollen-limited reproduction in this species. If a large number of flowers within any inflorescence are pollinated artificially, however, resource limitations operate and pods from ovaries pollinated late in the season are aborted. On average, the maximum of ovaries developing into fruit within any inflorescence is 4. It is suggested that, in this nectarless species, about 80% of total are ‘excess’ flowers which contribute to increase pollinator attraction. Nerium oleander pollen is aggregated into a sticky substance, which allows the fertilization of many ovules after a single, probably rare, pollination event. Fruits are many seeded follicles (181 seeds per fruit on average), so that individual plants often liberate thousands of seeds in spite of the low percent fruit set. The hairy, water-dispersed seeds are released during the rainiest season in the year, and germination follows rapidly. All seedlings tracked died before completing 1 year of life, mostly because of desiccation during the first summer drought. Pollination by deceit in this Mediterranean species is discussed in terms of phylogenetic constraints within the mainly tropical family Apocynaceae.     

Flower opening and closing ofOxalis martiana

Flowers ofOxalis martiana open in the morning and close in the afternoon repeatedly for 3–5 days in May–July under natural conditions. Both in light and in darkness, the closed flowers opened in reponse to a rise in temperature (thermonasty), but not under the constant temperatures. Transfer from darkness to light along with temperature rise caused rapid flower opening, and at 20 C or higher temperatures, exposure to light caused flower opening even without changing temperature (photonasty). Therefore, the temperature of the night before opening is critical in determining whether the flower opening under natural conditions depends on thermonasty or photonasty. The opened flowers closed about 8–11 hr after the beginning of opening both under natural conditions and constant light-temperature conditions, which suggests that the time of flower closing is determined by endogenous factors. Length of the perianth increased greatly during opening and slightly during closing. Application of actionomycin D or cycloheximide inhibited both the flower opening and closing, probably by suppressing the perianth growth.     

Nectar secretion dynamic links pollinator behavior to consequences for plant reproductive success in the ornithophilous mistletoe Psittacanthus robustus

The mistletoe Psittacanthus robustus was studied as a model to link flower phenology and nectar secretion strategy to pollinator behaviour and the reproductive consequences for the plant. The bright‐coloured flowers presented diurnal anthesis, opened asynchronously throughout the rainy season and produced copious dilute nectar as the main reward for pollinators. Most nectar was secreted just after flower opening, with little sugar replenishment after experimental removals. During the second day of anthesis in bagged flowers, the flowers quickly reabsorbed the offered nectar. Low values of nectar standing crop recorded in open flowers can be linked with high visitation rates by bird pollinators. Eight hummingbirds and two passerines were observed as potential pollinators. The most frequent flower visitors were the hummingbirds Eupetomena macroura and Colibri serrirostris, which actively defended flowering mistletoes. The spatial separation between anthers, stigma and nectar chamber promotes pollen deposition on flapping wings of hovering hummingbirds that usually probe many flowers per visit. Seed set did not differ between hand‐, self‐ and cross‐pollinated flowers, but these treatments set significantly more seeds than flowers naturally exposed to flower visitors. We suggest that the limitation observed in the reproductive success of this plant is not related to pollinator scarcity, but probably to the extreme frequency of visitation by territorial hummingbirds. We conclude that the costs and benefits of plant reproduction depend on the interaction strength between flowers and pollinators, and the assessment of nectar secretion dynamics, pollinator behaviour and plant breeding system allows clarification of the complexity of such associations.     

Insect preference for symmetrical artificial flowers

An insect preference for floral symmetry may be maintained because plants with symmetrical flowers, which are able to control developmental processes under given environmental conditions, also are able to provide more pollinator rewards than plants with asymmetrical flowers. Alternatively, insects may have an inherent preference for symmetrical structures and thereby impose selection for the maintenance of symmetry in flowers even in the absence of any pollinator rewards. We tested for an insect preference for radially symmetrical flowers by using horizontally placed units of four circular coloured flower models varying in size and symmetry. The shape and colour of the model flowers did not resemble any naturally occurring flowers in the environment. Insects and Hymenoptera, respectively (five species of Diptera and one species of Coleoptera) that visited the flower models clearly preferred symmetrical models over asymmetrical ones, and the ranking of visits to the models reflected a preference for large, symmetrical flowers. These results provide evidence for a preference for symmetrical flower models, even in the absence of pollinator rewards. Received: 11 September 1997 / Accepted: 2 November 1997     

POLLINATOR EFFECTIVENESS AND SEED SET IN POPULATIONS OF AGALINIS STRICTIFOLIA (SCROPHULARIACEAE)

Examining variation in pollinator effectiveness and seed production resulting from single pollinator visits can provide a deeper understanding of how pollinators may influence reproduction in plant populations. When comparing populations, differences in the number of seeds produced from single pollinator visits to flowers may not always be attributable to differences in pollen deposition, but rather to differences in plant fecundity or resource availability. Pollinator effectiveness and seed production were studied for two populations over a 4-year period and were measured using single bee visit manipulations of flowers. No significant difference in pollinator effectiveness (pollen deposited on stigmas) was observed between the two populations. However, a significant difference between the two populations was observed in the number of seeds produced per flower. The Wellhouse population produced approximately three times as many seeds/flower from a single pollinator visit as did the Firefly Meadow population. Within each population, pollinators (Bombus pennsylvanicus and Apis mellifera) did not differ in the number of pollen grains deposited on stigmas or seeds produced per flower from single visit experiments. Differences in plant density, pollen viability, and ovules per flower also could not account for a significant amount of the variation. A resource augmentation experiment (water and fertilizer application) resulted in a decrease in seeds per flower per bee visit for the water treatment at the Wellhouse population only. For both populations, pollen deposition, pollen viability, and ovules per flower were unaffected by the resource augmentation. Alternative possibilities for the observed differences in seeds per flower per bee visit are discussed.     

早春短命植物黑鳞顶冰花的花粉呈现时序及其适应性

花粉的时序呈现是指植物花药按一定次序释放花粉的现象, 被认为是对传粉者访问频率的一种适应。在传粉者充足的环境中, 植物通过限制花粉1次被移出的数量, 使花粉供体能作为多个父本, 从而提高雄性适合度。该文从开花习性、花部特征、传粉者及繁育系统等方面对早春短命植物黑鳞顶冰花(Gagea nigra)的花粉呈现时序及其适应性进行研究, 结果表明, 黑鳞顶冰花单花期约5-7天; 白天开放, 晚上闭合, 花药次序开裂, 呈拉链式散粉, 散粉期4-6天。黑鳞顶冰花以异交为主, 部分自交亲和。蝇类和食蚜蝇为主要传粉者, 访花频率为(0.141±0.078) flower∙h^-1。在雄蕊的时序散粉过程中, 雌蕊持续生长, 经历了从低于雄蕊到等高、再到高于雄蕊阶段。在等高阶段, 单花早晚的开闭, 使得雌雄蕊紧靠在一起, 促成了自动自花授粉。在传粉者缺乏的环境中, 黑鳞顶冰花的花粉时序呈现延长了散粉期, 在等待传粉者和分摊风险方面具重要作用。这种花粉渐次呈现的策略, 在新疆的早春开花植物中可能广泛存在。     

新疆胡颓子属植物花部性状的变异及其分类学价值

新疆胡颓子属植物栽培历史久、变异丰富、种下变异类型多、分类较为困难,因此有必要进一步发掘该属落叶组植物的分类学特征,尤其是对相对保守的繁殖器官的性状进行筛选。该研究以形态较为稳定的繁殖器官为切入点,分析花部性状的变异特点,筛选稳定性状,以期为解决该属的分类难题提供依据。先采用定株采集和同花标记的方法,对比分析了柱头形态、花盘先端有毛无毛、花柱与雄蕊的长短比、花被裂片程度四个性状的稳定性。结果表明:花盘先端有毛无毛、花柱与雄蕊的长短比、花被裂片程度三个性状较稳定,可以作为分类依据;柱头形态在单花中表现稳定,但在单株中出现极大的变异,不具有分类价值;然后采取新疆南、北疆地区的胡颓子属落叶组的尖果沙枣、大果沙枣和沙枣这三种来验证花部性状的稳定性,证明了上述结论的正确性,同时也是对该属分类研究实践的应用。该结果可为胡颓子属的经典分类学和形态学研究以及植物的开发和利用等提供参考依据。     

Morphology and development of the reproductive shoots of Lilaea scilloides (Poir.) Hauman (Alismatidae)

Shoots of adult plants of Lilaea scilloides have a sympodial form. Each unit of the sympodium bears a single sheathing prophyll (which is the only kind of foliage leaf produced in the adult) and terminates in an inflorescence. The prophyll subtends the next unit of the sympodium. A further accessory bud can form in association with each unit. This bud repeats the pattern of the main sympodium, giving the plant a tufted habit. Five different kinds of flower can be identified in the inflorescence: a unisexual male flower with a single perianth member and adnate stamen; a bisexual flower, with a single perianth member and adnate stamen, and a single carpel with an anatropous bitegmic ovule; a unisexual female flower with a single perianth member and carpel; a unisexual female flower comprising only a single carpel; and a female flower comprising only a single carpel with a very long filamentous style. The first four kinds occur in the upper part of the inflorescence which is normally elevated on a scape, while the last kind is restricted to the base of the inflorescence. In the position of the basal flowers several variations have been observed in cultivated material. These include branching associated with the basal flowers, which results in the development of additional basal flowers or inflorescences, and even total replacement of a basal flower by an inflorescence or a branching structure bearing flowers. A review of past literature includes a clarification of some persistent errors which have confused the taxonomic position of the plant and the morphological interpretation of the reproductive appendages.     

Reproductive assurance varies with flower size in Collinsia parviflora (Scrophulariaceae)

A central question in plant evolutionary ecology is how mixed mating systems are maintained in the face of selection against self-pollination. Recently, attention has focused on the potential reproductive assurance (RA) benefit of selfing: the ability to produce seeds via autonomous selfing when the potential for outcrossing is reduced or absent. To date, there is little experimental support for this benefit under natural pollination conditions. In addition, the RA hypothesis has not been tested experimentally in a species displaying morphological variation for traits expected to influence the mating system, such as flower size, which affects both attractiveness to pollinators and ability to self autonomously. Here, we document significant among-population variation in flower size in Collinsia parviflora and show that pollinators preferred large flowers over small flowers in experimental arrays. The pollinator community varied among three study sites, and two small-flowered populations had lower pollinator visitation rates than one large-flowered population. We compared seed production between intact flowers (can self) and experimentally emasculated flowers (require a pollinator) on large- and small-flowered plants. As predicted by the RA hypothesis, small-flowered plants show a greater RA benefit of selfing than large-flowered plants; emasculated, small flowers produced very few seeds, relative to intact, small flowers or either emasculated or intact, large flowers. We also show that the RA benefit is pollination-context dependent, differing between small- and large-flowered test sites, likely due to a combination of pollinator discrimination against small flowers and differences between test sites in the pollinator community. This paper is the first experimental evidence showing a trait-dependent RA benefit of selfing under natural pollination conditions.     

DETERMINANTS OF OUTCROSSING RATE IN A PREDOMINANTLY SELF-FERTILIZING WEED,DATURA STRAMONIUM (SOLANACEAE)

We measured outcrossing rates of several North Carolina populations of the annual weed Datura stramonium including both natural populations and experimental populations in which we manipulated plant spatial arrangement. Because capsules of D. stramonium typically produce hundreds of seeds and we used an easily scored genetic marker for flower and hypocotyl color, we could measure outcrossing rates accurately for both individual plants and single flowers. The population-wide estimates of outcrossing rates were surprisingly low for a species with showy, entomophilous flowers and ranged from 1.9% in an experimental population with a “clumped” spatial arrangement to 8.5% in an experimental population with a “dispersed” arrangement. These low values were not produced by pollinator discrimination among flower color morphs, as determined by outcrossing measurements on test plants of different colors and by direct observations of pollinator behavior. For individual plants and single flowers in the experimental populations, variation in outcrossing rates was significantly affected by such population-wide characteristics as plant spatial arrangement and nightly fluctuations in total floral abundance. However, by far the most important factor was stigma position. Flowers with stigmas above the anthers had significantly higher outcrossing rates than did flowers with overlapping stigma and anthers. The strong effect of floral morphology suggests that the very low population-wide levels of outcrossing in D. stramonium may represent a persistent mixing mating system rather than a transition to complete selfing.     

Studies on the breeding system of Limnocharis flava (Butomaceae)

Limnocharis flava ( Linn. ) Buch. normally produced 2 ～ 13 bisexual flowers in a cincinnus (seorpioid cyme). The anthesis of each flower lasted 5 ～ 13 hours. In natural populations, two species of beetles were observed visiting the flowers in bloom. Several whorls of staminodes outside of the stamens limited the pollen to disperse outward, and made the pollen deposit only on the stigma of the same flower. After the perianth closed, the inner perianth changed into liquid which created a suitable environment for pollen germination. The pollen-ovule ratio, which ranged from 650 to 1120( 930±180) reflects an economical self-pollination system. As the fruits maturied, the inflorescence fell to ground or mud, and the vegetative buds (i.e. vegetative components ), developed at the apex of the inflorescence, grew into new vegetative shoots. One mother plant usually could produce 6 ～ 20 new vegetative shoots in a life cycle. One fruit of L. flava contained 470 ～ 640 seeds, with an average seed-set rate of about 80%. The seeds of Limnocharis flava could disperse a long distance and occupy new suitable habitats to establish new populations. The vegetative buds, however, predominantly could only spread to nearby places and thus enlarge the size of the population. Results from some artificial treatments, such as emasculating and netting, emasculating and bagging, hand-pollinating, netting, and bagging, indicate that L. flava is selfing in general but also cross-compatible. Based on the above results, it is considered that the breeding system of L. flava is predominantly selfing, but mixed with outcrossing, and the likely evolutionary tendencyis from outcrossing to selfing.     

Visual discrimination between two sexually deceptive <Emphasis Type="Italic">Ophrys</Emphasis> species by a bee pollinator

Almost all species of the orchid genus Ophrys are pollinated by sexual deception. The orchids mimic the sex pheromone of receptive female insects, mainly hymenopterans, in order to attract males seeking to copulate. Most Ophrys species have achromatic flowers, but some exhibit a coloured perianth and a bright, conspicuous labellum pattern. We recently showed that the pink perianth of Ophrys heldreichii flowers increases detectability by its pollinator, males of the long-horned bee Eucera berlandi. Here we tested the hypothesis that the bright, complex labellum pattern mimics the female of the pollinator to increase attractiveness toward males. In a dual-choice test we offered E. berlandi males an O. heldreichii flower and a flower from O. dictynnae, which also exhibits a pinkish perianth but no conspicuous labellum pattern. Both flowers were housed in UV-transmitting acrylic glass boxes to exclude olfactory signals. Males significantly preferred O. heldreichii to O. dictynnae flowers. In a second experiment, we replaced the perianth of both flowers with identical artificial perianths made from pink card, so that only the labellum differed between the two flower stimuli. Males then chose between both stimuli at random, suggesting that the presence of a labellum pattern does not affect their choice. Spectral measurements revealed higher colour contrast with the background of the perianth of O. heldreichii compared to O. dictynnae, but no difference in green receptor-specific contrast or brightness. Our results show that male choice is guided by the chromatic contrast of the perianth during the initial flower approach but is not affected by the presence of a labellum pattern. Instead, we hypothesise that the labellum pattern is involved in aversive learning during post-copulatory behaviour and used by the orchid as a strategy to increase outcrossing.     

Flower Structure and Reproductive Biology of Bougainvillea stipitata (Nyctaginaceae)

Abstract: Bougainvillea stipitata displays inflorescences with three pendant greenish flowers. Flowers open at sunset and last five days. Flower perianth is constricted in the middle and forms a tube that ends in five lobes. Fragrance is emitted by the papillae located on the lobe margins of the perianth. The nectary is located at the base of the staminal tube. It secretes fructose-dominant nectar with amino acids, phenols and reduced acids. Nectar secretion is continuous during flower lifetime and the flowers do not recover the reward. Mainly moths visit flowers. Pollen load on stigmas indicates that most flowers received more than 50 pollen grains, which are deposited by pollinators within the first two days of the flower life. Although the low natural fruit set of this self-incompatible species may be due to intraplant pollen flow, pollinators play an essential role for B. stipitata fruit production.     

Pollinator responses to variation in floral display and flower size in dioecious Sagittaria latifolia (Alismataceae)

In animal-pollinated plants with unisexual flowers, sexual dimorphism in floral traits may be the consequence of pollinator-mediated selection. Experimental investigations of the effects of variation in flower size and floral display on pollinator visitation can provide insights into the evolution of floral dimorphism in dioecious plants. Here, we investigated pollinator responses to experimental arrays of dioecious Sagittaria latifolia in which we manipulated floral display and flower size. We also examined whether there were changes in pollinator visitation with increasing dimorphism in flower size. In S. latifolia, males have larger flowers and smaller floral displays than females. Visitation by pollinators, mainly flies and bees, was more frequent for male than for female inflorescences and increased with increasing flower size, regardless of sex. The number of insect visits per flower decreased with increasing floral display in males but remained constant in females. Greater sexual dimorphism in flower size increased visits to male inflorescences but had no influence on the number of visits to female inflorescences. These results suggest that larger flower sizes would be advantageous to both females and males, and no evidence was found that females suffer from increased flower-size dimorphism. Small daily floral displays may benefit males by allowing extended flowering periods and greater opportunities for effective pollen dispersal.     

FLORAL BIOLOGY,HUMMINGBIRD POLLINATION AND FRUIT PRODUCTION OF TRUMPET CREEPER (CAMPSIS RADICANS,BIGNONIACEAE)

Trumpet creeper is self-incompatible and bears long, tubular, orange flowers from June to September. Flowering peaks rapidly, then declines and continues at low levels for several weeks. The initial burst of flowering may attract pollinators that return even during subsequent reduced flowering. Most flowers open before noon and nectar production totals 110 μl of 26% sucrose equivalents per flower, an exceptionally high production for a temperate zone plant. Production ceases within 20–30 hr of flower opening, but corollas persist for several days and may serve to attract pollinators. Effective pollination reduces the period of stigma receptivity and speeds closing of stigma lobes. Only 1–9% of flowers produced mature fruits at four sites in Illinois and Missouri. Roughly 400 pollen grains had to be deposited on a receptive stigma to cause fruit development beyond an initial period of high abortion. At two sites, 17% and 89% of stigmas received over 400 pollen grains. Assuming 50% of deposited grains were from the same plant, fruit production at one site was clearly pollinator limited, that at the second site may have been. Ruby-throated Hummingbirds (Archilochus colubris) deposited ten times as much pollen per stigma per visit as honeybees (Apis mellifera) and bumblebees (Bombus spp.). Fruit set was highest where rubythroat visitation was most frequent. Trumpet creeper appears primarily adapted for hummingbird pollination, but can also be adequately pollinated by honeybees and bumblebees. This is one of the first attempts to relate pollen-depositing capabilities of pollinators of any plant to pollen requirements for fruit production. Several characteristics suggest that trumpet creeper may be adapted to pollination at low densities (often called traplining) in its presumed original, woodland, habitat.     

Both biotic and abiotic factors influence floral longevity in three species of Epidendrum (Orchidaceae)

Extended flower longevity has been widely defended to occur as a consequence of low pollination activity. To test this hypothesis in Neotropical rainforests, we selected three species of Epidendrum that flower during rainy conditions and commonly exhibit low levels of insect visits. Experimental studies carried out in 15 populations distributed along a wide spatial gradient detected the presence of pollinator limitation in all populations. Pollinia removal without pollen deposition increased longevity, and thus extended longevity could apparently be considered as an ecological advantage for these orchids. Nevertheless, flower longevity was severely shortened by abiotic factors like precipitation and humidity. Comparison with other tropical orchids showed that flower longevity was higher even in species that flower during periods of more pollinator activity than the ones studied here, which is contrary to the hypothesis that pollinators are the only driving force for long‐lived flowers in Epidendrum. Thus, although long floral longevities are apparently favorable for the reproductive success of these species, the high maintenance costs experienced during rainy conditions are also an important factor constraining the selection of long‐lived flowers in Epidendrum.     

Changes in Florets’ Vertical Direction within Inflorescence Affects Pollinator Behavior,and Fitness in <i>Trifolium repens</i>

Ecological interactions between flowers and pollinators greatly affect the reproductive success. To facilitate these interactions, many flowers are known to display their attractive qualities, such as scent emission, flower rewards and floral vertical direction, in a rhythmic fashion. However, less is known about how plants regulate the relationship between these flower traits to adapt to pollinator visiting behavior and increase reproduction success. Here we investigated the adaptive significance of the flower bending from erect to downward in Trifolium repens. We observed the flowering dynamic characteristics (changes of vertical direction of florets, flowering number, pollen grain numbers, pollen viability and stigma receptivity over time after blossom) and the factors affecting the rate of flower bending in T. repens. Then we altered the vertical direction of florets in inflorescence of different types (upright and downward), and compared the pollinator behaviors and female reproductive success. Our results showed that florets opened sequentially in inflorescence, and then bend downwards slowly after flowering. The bending speed of florets was mainly influenced by pollination, and bending angle increased with the prolongation of flowering time, while the pollen germination rate, stigma receptivity and nectar secretion has a rhythm of “low-high-low” during the whole period with the time going. The visiting frequency of all the four species of pollinators on upward flowers was significantly higher than that of downward flowers, and they especially prefer to visit flowers with a bending angle of 30°–60°, when the flowers was exactly of the highest flower rewards (nectar secretion and number of pollen grains), stigma receptivity and pollen germination rate. The seed set ratio and fruit set ratio of upward flowers were significantly higher than downward flowers, but significantly lower than unmanipulated flowers. Our results indicated that the T. repens could increase female and male fitness by accurate pollination. The most suitable flower angle saves pollinators’ visiting energy and enables them to obtain the highest nectar rewards. This coordination between plants and pollinators maximizes the interests of them, which is a crucial factor in initiating specialized plant-pollinator relationships.     

Variation in inflorescence size in a dioecious fig tree and its consequences for the plant and its pollinator fig wasp

The host-specific relationship between fig trees (Ficus) and their pollinator wasps (Agaonidae) is a classic case of obligate mutualism. Pollinators reproduce within highly specialised inflorescences (figs) of fig trees that depend on the pollinator offspring for the dispersal of their pollen. About half of all fig trees are functionally dioecious, with separate male and female plants responsible for separate sexual functions. Pollen and the fig wasps that disperse it are produced within male figs, whereas female figs produce only seeds. Figs vary greatly in size between different species, with female flower numbers varying from tens to many thousands. Within species, the number of female flowers present in each fig is potentially a major determinant of the numbers of pollinator offspring and seeds produced. We recorded variation in female flower numbers within male and female figs of the dioecious Ficus montana growing under controlled conditions, and assessed the sources and consequences of inflorescence size variation for the reproductive success of the plants and their pollinator (Kradibia tentacularis). Female flower numbers varied greatly within and between plants, as did the reproductive success of the plants, and their pollinators. The numbers of pollinator offspring in male figs and seeds in female figs were positively correlated with female flower numbers, but the numbers of male flowers and a parasitoid of the pollinator were not. The significant variation in flower number among figs produced by different individuals growing under uniform conditions indicates that there is a genetic influence on inflorescence size and that this character may be subject to selection.     

多叶斑叶兰繁育系统与传粉生物学研究

为探讨多叶斑叶兰(Goodyera folisa)的繁育系统与传粉生物学特征,对其开花物候、花粉活力与柱头可授性、人工授粉、花的挥发性成分以及昆虫传粉行为进行了研究。结果表明,多叶斑叶兰的唇瓣黄色,萼片白色或白色带红褐色;单花花期为(9.4±0.8)d;花粉在开花后第1天具备活力,柱头在开花后第2天具备可授性,花粉活力和柱头可授性都在开花后第5天达到峰值。去雄套袋和不去雄套袋都不能结实,人工自花授粉、同株异花授粉和异株异花授粉的结实率分别为93.3%、95.0%和96.7%,自然结实率为43.3%。花朵的主要挥发性成分为1-辛烯-3-醇、3-辛醇和N,N-二甲基甲酰胺。多叶斑叶兰传粉者为中华蜜蜂(Apis cerana)。多叶斑叶兰具有自交亲和能力,但在自然界不具有主动自交现象,必须依赖中华蜜蜂传粉,花色及花香气味为吸引传粉者的主要因素。     

Optimal resource allocation model for excessive flower production in a pollinating seed-predator mutualism

Many plants produce excessive flowers and several hypotheses have been proposed for adaptive significances of this behavior. Here, I develop a simple resource allocation model for plants in a mutualism with pollinating seed-predators to examine a novel hypothesis that excessive flower production can be favored to “dilute” seed predation by the pollinators. Pollinators visit flowers to deposit pollen and oviposit on them, and their offspring feed on a portion of the seeds, leaving the remainder intact. Further pollinator visits increase seed mortality by over-oviposition. Excessive flower production is favored if it decreases pollinator-visit frequency per flower, while it incurs decrease in seed production because of the resource trade-off. I examine three plant strategies: (1) no abortion, the plant allocates resource to all pollinated flowers to mature; (2) selective abortion, the plant aborts flowers depending on how many times they were visited by pollinators; and (3) random abortion, the plant indiscriminately aborts a fraction of pollinated flowers irrespective of how many times they were visited. I show that the random abortion strategy can perform much more effectively than the no-abortion strategy when the amount of resource is small, the production cost per flower is low, and the pollinator density is high, although the selective abortion strategy is always the best. This “predator dilution” effect has not been considered with regard to previous excessive flower production hypotheses.