Pollination in conifers

Our understanding of pollination in conifers has advanced rapidly in recent years, but it still lags behind our knowledge of this process in angiosperms. In part this is because conifers are not considered to be high priority crops and, unlike many cultivated flowers, conifer seed cones are generally neither large nor colorful. The use of genetics to improve tree growth has primarily been through selection and asexual propagation rather than breeding, and because incompatibility is not thought to occur in conifer pollination systems, concern about pollination has primarily been with regard to seed production. Here we examine the ancestral wind-pollination mechanism in conifers and discuss how the process may have evolved to improve pollination success.     

Surface and submarine pollination in the seagrass Zoster a marina L

COX, P. A., LAUSHMAN, R. H. & RUCKLESHAUS, M. H., 1992. Surface and submarine pollination in the seagrass Zostera marina L. Hydrophilous plants can be divided into three ecological categories depending upon whether their pollen is transported above, on, or under the water surface. A mixed mode of submarine and surface hydrophilous pollination occurs in the seagrass Zostera marina L. In the surface mode of pollination, pollen rafts or 'search vehicles' which superficially resemble snowflakes, form at low tide and are transported on the surface of the sea by winds and water currents. Some of the search vehicles collide with the floating female stigmas, effecting pollination. In the submarine mode of pollination, small pollen masses resembling whisk brooms travel beneath the surface of the water. Although we failed to observe a submarine pollination event, SEM analysis of stigmas from subtidal populations confirms that submarine pollination does occur in Z. marina . However, observations of stigmas positioned at and below the surface of the water show surface pollination to be highly efficient. Electrophoretic evaluation of both subtidal and intertidal populations indicates significant genetic variation between populations. Given the high flux rates of surface-borne pollen and pollen viability in excess of 5 h, it is likely that surface-borne pollen is a major source of gene flow in Zostera marina populations.     

中国农业生态系统昆虫授粉功能量与服务价值评估

所有开花植物中大约有80%的物种需要动物作为授粉媒介。系统介绍了中国重要栽培作物花的结构和类型,授粉过程、媒介和方式,作物对昆虫授粉的依赖程度,昆虫授粉功能与服务的概念,以及昆虫授粉功能量与服务价值量的评估方法;同时评估了我国各省农业生态系统中昆虫对重要作物的授粉功能量与服务价值量。结果表明:粮食作物、水果作物、蔬菜作物和经济作物不同程度的依赖昆虫授粉。根据2015年主要农作物产量、作物产品价格、昆虫授粉依赖程度等数据,计算得出昆虫对我国22类主要农作物的授粉功能量为1.8亿吨农产品产量和授粉服务价值为8860.5亿元(占当年GDP的1.3%),具有巨大的经济价值。2015年昆虫对主要栽培作物的授粉功能量和服务价值排在前五名的都是山东、河南、河北、陕西和新疆,年授粉服务价值均大于500亿元,反映出这5个省的主要农作物对昆虫授粉依赖程度较高。昆虫对作物的授粉功能量评价有助于了解昆虫对作物生物量或产量的生物学和生态学效应以及作物对昆虫授粉的需求。昆虫对作物的授粉服务价值评估有助于掌握昆虫授粉为人类所带来的经济效应或经济价值,并帮助决策维持或增强授粉昆虫多样性和种群数量的人力、物力和财力投入。     

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.     

双翅目昆虫传粉研究进展

昆虫传粉不仅在自然生态系统中发挥着十分重要的作用,也和农业生态系统中产量密切相关。众所周知,膜翅目昆虫是最重要的传粉昆虫。双翅目昆虫分布广,物种多,数量大,也是一类十分重要的传粉昆虫,但其传粉作用未受到足够的重视。本文主要综述了双翅目传粉昆虫的主要种类、传粉效力、传粉特征、与植物的协同进化以及双翅目昆虫传粉的生态学意义。据记载双翅目昆虫中至少有71个科涉及虫媒种类,目前有资料显示访花昆虫类群中双翅目约有54 417种,按涉及的种数排序居于昆虫纲传粉昆虫目中第4位。尽管双翅目昆虫单次访问可携带花粉量相对较少(相比于膜翅目),但是较高访问速率及庞大的个体数量,保证了其作为有效传粉者的地位。传粉综合征能够有效揭示植物与传粉者的协同进化关系,尤其是对一些专化传粉现象(如五味子科-瘿蚊系统)和泛化传粉的深入研究,更加深了我们对协同进化的理解。就生态学意义而言,一方面双翅目传粉昆虫是膜翅目传粉昆虫的有益补充,另一方面在一些特殊环境中,双翅目昆虫具有不可替代的作用。当前传粉昆虫(包括双翅目)数量急剧下降,而且双翅目昆虫的传粉价值还利用较少。结合我国当前的研究现状提出了以下未来研究重点:1)加深双翅目传粉效力和适应意义的案例研究以明确双翅目昆虫在传粉体系中的地位;2)加强栖息地格局变化与昆虫多样性的研究以明确栖息地改变对昆虫的影响程度;3)梳理访花和传粉、专化传粉和泛化传粉等关系以更加明确双翅目昆虫在与植物协同进化中的作用;4)逐步深入探讨花粉浪费和花粉竞争以探究传粉策略和植物繁殖策略。这些努力将为双翅目传粉昆虫的知识普及、资源保护与利用研究等方面提供参考。     

Pollination biology of the endangered orchid Cypripedium japonicum in a fragmented forest of Japan

Pollination biology studies of the endangered orchid Cypripedium japonicum were conducted in its natural habitat using pollinator observation and hand‐pollination experiments. The observed fruit set was as follows: artificial outcross‐pollinated, 100%; artificial self‐pollinated, 100%; pollinator‐excluded, 0%; and emasculated flowers, 0%. These results show that this species, although self‐compatible, is neither autogamous nor agamospermous. The fruit set for open‐pollinated flowers was 14.9%, which suggests that the study population was subject to pollinator limitation. The nectarless flowers of C. japonicum were exclusively visited and pollinated by the queens of two bumblebee species (Bombus ardens and B. diversus diversus). It is probable that the nectarless flowers of C. japonicum attract pollinators through a generalized food deceptive system.     

Pollination Ecology and Effect of Nectar Removal in Macleania bullata (Ericaceae)1

The floral syndrome of Macleania bullataYeo (Ericaceae) reflects its adaptation to hummingbird pollination. Its flowers, however, are subject to high levels of nectar robbing. I examined the floral visitor assemblage of M. bullata in a tropical montane wet forest in southwestern Colombia, focusing on the behavior of the visitors. I also tested for the presence of nocturnal pollination and the effects of nectar removal on new nectar production. The principal floral visitors were the nectar robbing hummingbirds Ocreatus underwoodii (19.1% of visits) and Chlorostilbon mellisugus (18.9%). Only two species of long–billed hummingbirds visited the flowers of M. bullata as “legitimate” pollinators: Coeligena torquata (14.7% of visits) and Doryfera ludoviciae (14.3%). The remaining visits constituted nectar robbing by bees, butterflies, and other species of hummingbirds. Nocturnal pollination took place, although fruit set levels were 2.4 times higher when only diurnal pollination was allowed as opposed to exclusively nocturnal pollination. Nectar robbers removed floral nectar without pollinating the flower. Treatments of experimental nectar removal were carried out to examine if flowers synthesize more nectar after nectar removal. Nectar removal increased the total volume of nectar produced by each flower without affecting sugar concentration. Thus, nectar robbing can impose a high cost to the plants by forcing them to replace lost nectar.     

Floral trait evolution associated with shifts between insect and wind pollination in the dioecious genus Leucadendron (Proteaceae)

Transitions between animal and wind pollination have occurred in many lineages and have been linked to various floral modifications, but these have seldom been assessed in a phylogenetic framework. In the dioecious genus Leucadendron (Proteaceae), transitions from insect to wind pollination have occurred at least four times. Using analyses that controlled for relatedness among Leucadendron species, we investigated how these transitions shaped the evolution of floral structural and signaling traits, including the degree of sexual dimorphism in these traits. Pollen grains of wind‐pollinated species were found to be smaller, more numerous, and dispersed more efficiently in wind than were those of insect‐pollinated species. Wind‐pollinated species also exhibited a reduction in spectral contrast between showy subtending leaves and background foliage, reduced volatile emissions, and a greater degree of sexual dimorphism in color and scent. Uniovulate flowers and inflorescence condensation are conserved ancestral features in Leucadendron and likely served as exaptations in shifts to wind pollination. These results offer insights into the key modifications of male and female floral traits involved in transitions between insect and wind pollination.     

环纹榕传粉榕小蜂的传粉模式

榕小蜂的传粉结构、 传粉行为以及寄主榕树的花药胚珠比是判断榕-蜂互惠系统传粉模式的重要依据。本研究于2010年8月至2011年6月对位于云南西双版纳地区的试验样树环纹榕Ficus annulata进行观察, 对出榕果的环纹榕传粉榕小蜂Deilagaon annulatae进行电镜扫描和室内显微镜下对其进行行为观察。电镜扫描显示： 环纹榕传粉榕小蜂D. annulatae位于胸部的花粉筐消失, 具一片可粘附花粉的毛区, 提示其属于被动传粉的种类。传粉行为观察发现, 该蜂没有主动采集花粉的行为, 显然存在的花粉刷已丧失了主动收集花粉的功能。寄主植物环纹榕F. annulata属于典型的自动散粉让榕小蜂沾附花粉的榕树种类。环纹榕传粉榕小蜂D. annulatae是西双版纳热带地区已知58种传粉榕小蜂中唯一体色为黄色的种类, 该蜂偏爱在低温的夜晚出蜂。除了传粉榕小蜂, 一种金小蜂Lipothymus sp.也在雌花期进入榕果内繁殖, 并且其数量显著高于环纹榕传粉榕小蜂D. annulatae (P<0.0001)。自然单果的繁殖中, 环纹榕传粉榕小蜂的数量显著高于种子数量, 呈现出榕-蜂互惠系统中罕见的传粉榕小蜂主导的局面。综合榕-蜂的传粉特征显示, 环纹榕F. annulata及其传粉榕小蜂D. annulatae互惠系统是被动传粉的模式。     

Interannual fluctuations in floral longevity, pollinator visitation and pollination limitation of an alpine plant (Gentiana straminea Maxim., Gentianaceae) at two altitudes in the Qinghai-Tibetan Plateau

Prolonged floral longevity and bumblebees as dominate pollinators in alpine ecosystem have been suggested to overcome pollination limitation of alpine plants arising from the decrease of pollinator activity with increasing altitude. However, this conclusion has never been examined in the Qinghai-Tibetan Plateau (QTP), the highest and largest plateau in the world. In this study, we intended to test year-to-year correlations between floral longevity, visiting frequency and pollen limitation of this species between two populations (at 3200 m and 4000 m) of Gentiana straminea in this plateau. Pollinator exclusion elongated both male and female phases greatly at both sites, and durations of both male and female phases in natural condition varied greatly over three years. The visiting frequency of bumblebees varied greatly at the higher altitude, but seemed to be stable at the lower altitude. Seed production was pollination limited in both populations in most studied years. The floral durations, pollinator frequency and pollination limitation showed no significant and consistent variations with the increase of altitude. The previous hypothesis that the prolonged floral longevity of alpine plants can compensate for low levels of pollinator visitation therefore could not be confirmed, and our results further suggested that in the QTP platform, the altitude shows no consistent effect on the reproductive performance of this species, despite that the fluctuation of visit frequency intensified at the higher altitude.     

Crane flies and microlepidoptera also function as pollinators in Epidendrum (Orchidaceae: Laeliinae): the reproductive biology of E. avicula

Crane flies and microlepidoptera have been recorded as pollinators in unrelated orchid groups, but these insects have never been recorded in Epidendroideae, the most species‐rich orchid subfamily, which includes one of the most diverse genera among Orchidaceae, Epidendrum. Based on data on phenology, floral morpho‐anatomy, pollinators, pollination mechanisms and breeding system, the reproductive biology of E. avicula was studied in south‐eastern Brazil. Epidendrum avicula possess osmophores that produce a citric fragrance at night. The flowers attract Tipulidae flies and several families of microlepidoptera that drink the nectar produced in a tube formed by the adnation of the labellum and column. As is common in Epidendrum, after removing the pollinarium, both crane flies and micro‐moths get trapped by the proboscis, which frightens the insects and inhibits any possible intent to immediately visit another flower. The behavior of the pollinators on flowers, plus the retention of the anther cap by the pollinarium, results in a reduction in the occurrence of geitonogamy. Because E. avicula is self‐incompatible, the consequence of pollinator behavior and the floral mechanisms tend to reduce the pollen loss. As far as we know, this is the first study to report the reproductive biology of a species of Epidendroideae pollinated by crane flies and microlepidoptera. Based on more recent concepts of plant–pollinator interactions, although E. avicula is pollinated by several species belonging to two distinct orders, suggesting an unspecialized pollination system is involved, nectar‐seeking microlepidoptera and Tipulidae flies can be recognized as a single functional group.     

植物繁殖生态学的若干重要问题

发现模式,并根据过程解释模式,是科学研究的主要目标.在植物繁殖生态学领域内,人们已经总结了一些重要的模式,包括普遍的雌雄同体、分离的花果期、较低的结实率、大量的同时开花、胁迫生境更易出现的异交、生活史性状与交配系统的相互作用、花序内的花分化,以及花内的雄蕊分化(异型雄蕊)等.对这些模式如何从机理上予以解释,还需要植物繁殖生态学家的艰苦努力.本文着重强调了植物许多重要繁殖特征都可以通过植株、花序以及花各层次上的资源分配而得到很好的解释,尤其是可以在很大程度上协调其他不同侧重点研究得到的矛盾结论.在今后逐渐强调多因素、多尺度对花部特征与传粉系统的适应与进化的研究中,从直接决定花部特征与交配系统的资源分配出发,将是促进人们准确理解与预测花部特征适应与进化的一个重要研究方向.     

Fidelity of Hymenoptera and Diptera pollinators in onion (Allium cepa L.) pollination

Onion (Allium cepa L.) is protandrous in nature and requires cross‐pollination to avoid inbreeding. The pollination potential of native bees (Hymenoptera) and true flies (Diptera) was assessed in the perspective of finding the best pollinators for onion cross‐pollination and seed multiplication. The community of pollinators was composed of four bee species and twelve true fly species. Episyrphus balteatus, Eupeodes sp., Musca domestica and Eristalinus aeneus were the most abundant pollinators. The maximum pollinator activity was observed from 12 to 24 days after opening of the flowers. The pollination effectiveness of tested bees (Apis dorsata and Apis florea) was greater than true flies (E. balteatus, Eupeodes sp., M. domestica, E. aeneus and Callihoridae sp.) in terms of Spears values.     

Convergence of filiform pollen morphologies in seagrasses: Functional mechanisms

Summary The peculiar filiform pollen morphology and ability to pollinate in an aquatic medium have evolved convergently in the marine angiosperms or seagrasses. A comparison of these systems with freshwater ones, reveals that reproductive strategy alone does not provide sufficient information to understand this convergence. Several models have, however, been proposed to explain the function and evolution of seagrass pollen morphologies. The first is a mathematical model, random search theory, which requires pollen to travel both randomly and perpendicularly to its path. It is elegant conceptually, but does not hold up to physical and empirical scrutiny. Conversely, a biophysical model, which requires pollen to obey the fluid dynamic principles of boundary-layer flow, may be complicated conceptually, but it is consistent with mathematics and nature. The correct modelling of pollination mechanisms in seagrasses provides an understanding of contemporary adaptations as well as the processes that selected them.     

Pollination biology and outcrossing rates in hermaphroditic Schiedea lydgatei (Caryophyllaceae)

The influence of outcrossing and pollination biology on the maintenance of hermaphroditism was studied for Schiedea lydgatei (Caryophyllaceae: Alsinoideae), a species endemic to Moloka`i in the Hawaiian Islands. Schiedea lydgatei is the only hermaphroditic species in an otherwise dimorphic clade and hermaphroditism is likely the result of a reversal from a gynodioecious ancestor. Both wind and native moths in the family Pyralidae are responsible for pollination in S. lydgatei. Outcrossing rates were generally high (0.80), especially in years when the greatest number of plants were flowering. The combination of high outcrossing rates and substantial inbreeding depression indicates that at present females would not be favored in the population. Pollination by both wind and insects is consistent with the hypothesis that hermaphroditism is the result of a relatively recent reversal, as the ancestor of S. lydgatei was probably wind pollinated and gynodioecious with few females in the populations. A shift from wind to predominately insect pollination on Moloka`i may have resulted in increased outcrossing rates and prevented the expression of high inbreeding depression among progeny of hermaphrodites, a condition that would select against females and favor a reversal to hermaphroditism. Because few females were likely to have been present in ancestral populations that colonized Moloka`i, founder effect is another potential explanation for loss of females. In either case, current high levels of outcrossing prevent re-establishment of females in populations of S. lydgatei.     

An affordable apparatus for fine‐controlled emulation of buzzing frequencies of bees for the testing hypothesis in buzz interactions

The buzzing foraging behavior of female bees for pollen harvesting called the attention of early pollination biologists. Flower types that demand this buzzing behavior comprise about 20,000 species of different and phylogenetically unrelated plant taxa, suggesting that it had independently evolved many times among the flowering plants. Between the late 1970s and early 1980s, theoretical papers had modeled the energetics of buzz pollination, but, up to this moment, no hypothesis was experimentally tested concerning the theoretical basis of the energetics of buzz pollination. We present a cost‐effective and simple apparatus, including a digital and highly accurate frequency generator, and a device for the transference of buzz‐frequency energy to the receptive floral unity. The receptive floral unities may comprise the entire or partial androecium, or the tubular corolla, or, in some cases, the whole flower. This apparatus can be easily used in both laboratory and field conditions of research, as natural air currents are avoided, and the response of pollen liberation can be quantitatively measured by pollen grain counts that can be captured by adhesion in slide poured with an isosmotic lactate–glycerol media. The maximum displacement of the hardwire beam/claw system was 0.1170 ± 0.0006 mm @ 150 Hz; 0.021 ± 0.003 mm @ 250 Hz; 0.010 ± 0.001 mm @ 350 Hz; 0.0058 ± 0.0001 mm @ 450 Hz; and 0.0082 ± 0.0005 mm @ 550 Hz. Hypothesis contrasting frequency emission and pollen liberation measured as pollen grain counts may be tested in a species flower type by simple linear regression if pollen counts are normally distributed, or ordinal logistic regression, with non‐normal counts. The comparison among different flower‐type requirements can be tested through appropriate statistical methods for both normally and non‐normally distributed pollen grain counts.     

Pollination specialization and time of pollination on a tropical Venezuelan plain: variations in time and space

Levels of specialization of the pollination systems were evaluated in 155 plant species from the Venezuelan Central Plain. In all, 29 pollination systems were found, resulting from various combinations of nine pollen‐vector types or pollinating agent classes. The number of pollen‐vector types composing a pollination system ranged from one to five. Ninety‐one species were pollinated by only a single pollen‐vector type; the frequency of pollination systems fell monotonically with increasing number of constituent pollen‐vector types. Some 30–40 per cent of bee‐, moth‐, beetle‐ and bat‐pollinated species were pollinated by that group of vectors alone. The highest incidence of co‐occurrence between pollen‐vector types was found for the combinations fly–wasp, butterfly–wasp, butterfly–fly, and to a lesser extent bird–butterfly, bat–bird, bat–moth and butterfly–moth. The average number of pollen‐vector types per plant species was significantly higher for trees and shrubs than for lianas and perennial herbs. The distribution of polyphily, oligophily, monophily and anemophily was significantly associated with life form and habitat. The relative frequencies of these types varied least through the year in the forest‐savannah ecotone and in the vegetation as a whole, reflecting the combination of life forms. There were significantly fewer night‐pollinated than day‐pollinated species. Day‐pollinated species tended to be polyphilous, and most of the night‐pollinated species were monophilous or oligophilous. Time of pollination activity was related to habitat. The relative importance of night pollination among life forms decreased from trees to perennial herbs. Plant species exclusively pollinated during the night reached a peak during the rainy season (May to November) for trees, lianas and perennial herbs. The data as a whole show that the relative frequency of polyphily, oligophily, monophily and anemophily, and the time of pollination activity are influenced by community structure and plant species richness, and may change from season to season. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 145 , 1–16.