Orientation and withdrawal of pollination drops in Cupressaceae s. l. (Coniferales)

Pollination in the Cupressaceae is studied ex situ, focused on orientation and withdrawal of pollination drops. Orientation of pollination drops is a constant feature in most taxa studied and important for pollen capture. Conspecific pollen causes a withdrawal of pollination drops, varying in time among species from 8 to 24 min, but with little variation within species. Pollination drops of each tested Cupressaceae taxon are also withdrawn when pollinated with foreign, but Cupressaceous pollen. However, they remain unchanged and are not withdrawn immediately when pollinated with pollen of other seed plants. The results clearly indicate that the time for the total withdrawal of pollination drops is strongly influenced by the evolutionary distance of the taxa being involved in the pollination process. Among closely related taxa the withdrawal is much more rapid than in distantly related ones. This points to an effective recognition system regulating the withdrawal of pollination drops, probably controlled by the nucellus. This recognition system can be regarded as an important preadaption for the evolution of a self-incompatibility mechanism. The withdrawal of pollination drops is thus not exclusively a physically induced process as suggested in some earlier studies. Pollination drops of several ovules can fuse to form a large common one, perhaps increasing by this way successful pollen capture.     

Adaptive plasticity of floral display size in animal-pollinated plants

Plants need not participate passively in their own mating, despite their immobility and reliance on pollen vectors. Instead, plants may respond to their recent pollination experience by adjusting the number of flowers that they display simultaneously. Such responsiveness could arise from the dependence of floral display size on the longevity of individual flowers, which varies with pollination rate in many plant species. By hand-pollinating some inflorescences, but not others, we demonstrate plasticity in display size of the orchid Satyrium longicauda. Pollination induced flower wilting, but did not affect the opening of new flowers, so that within a few days pollinated inflorescences displayed fewer flowers than unpollinated inflorescences. During subsequent exposure to intensive natural pollination, pollen removal and receipt increased proportionally with increasing display size, whereas pollen-removal failure and self-pollination accelerated. Such benefit-cost relations allow plants that adjust display size in response to the prevailing pollination rate to increase their attractiveness when pollinators are rare (large displays), or to limit mating costs when pollinators are abundant (small displays). Seen from this perspective, pollination-induced flower wilting serves the entire plant by allowing it to display the number of flowers that is appropriate for the current pollination environment.     

The impacts of pollination mode,plant characteristics and local density on the reproductive success of a scarce plant species, <Emphasis Type="Italic">Salix arbuscula</Emphasis>

Pollination failure represents one stage at which sexual reproduction of plants may be limited. It is therefore important to understand the pollination mechanism of the plant and how this may be affected by plant and population characteristics. This study examined the reproductive biology of a scarce montane willow species, Salix arbuscula, as part of a programme to determine ecological strategies for the conservation of montane willow scrub, an endangered habitat in the UK. The relative importance of insect and wind pollination, and the role of plant characteristics including plant size, catkin length, number of flowers and local density in determining reproductive success (number of fruit set) were investigated in three populations. Insect exclosures were used to determine the pollination mechanism. Our results suggest that S. arbuscula is predominantly insect-pollinated. In naturally pollinated plants, catkins with a higher proportion of ripe fruit were longer. Plants with more than two males in the local area and unbrowsed plants had a higher proportion of ripe fruit per catkin. The extent of wind pollination was very low, but differed between populations. The success of wind-only pollination was dependent on the number of males nearby, indicating that local density is more important in this type of pollination. Pollination mechanism and fruit set varied between the three populations observed, demonstrating the importance of multi-site comparisons. The number of males in the surrounding area had a positive effect on fruit set in both types of pollination, suggesting that Allee effects are likely to be operating in this species.     

The pollination niche and its role in the diversification and maintenance of the southern African flora

The flora of southern Africa has exceptional species richness and endemism, making it an ideal system for studying the patterns and processes of evolutionary diversification. Using a wealth of recent case studies, I examine the evidence for pollinator-driven diversification in this flora. Pollination systems, which represent available niches for ecological diversification, are characterized in southern Africa by a high level of ecological and evolutionary specialization on the part of plants, and, in some cases, by pollinators as well. These systems are asymmetric, with entire plant guilds commonly specialized for a particular pollinator species or functional type, resulting in obvious convergent floral evolution among guild members. Identified modes of plant lineage diversification involving adaptation to pollinators in these guilds include (i) shifts between pollination systems, (ii) divergent use of the same pollinator, (iii) coevolution, (iv) trait tracking, and (v) floral mimicry of different model species. Microevolutionary studies confirm that pollinator shifts can be precipitated when a plant species encounters a novel pollinator fauna on its range margin, and macroevolutionary studies confirm frequent pollinator shifts associated with lineage diversification. As Darwin first noted, evolutionary specialization for particular pollinators, when resulting in ecological dependency, may increase the risk of plant extinction. I thus also consider the evidence that disturbance provokes pollination failure in some southern African plants with specialized pollination systems.     

Intensified wind pollination mediated by pollen dimorphism after range expansion in an ambophilous biennial Aconitum gymnandrum

Pollination systems and associated floral traits generally differ between core and marginal populations of a species. However, such differences are rarely examined in plants with a mixed wind‐ and bumblebee‐pollination system, and the role of wind pollination during range expansion in ambophilous plants remains unclear. We compared floral traits and the contributions of bumblebee and wind pollination in refugium and marginal populations of the ambophilous plant Aconitum gymnandrum. We found that most floral traits differed between the two populations, and those traits associated with the shift to wind pollination were pronounced in the marginal population. Bumblebee visitation rates varied significantly, but were generally low in the marginal population. Wind pollination occurred in both populations, and the efficiency was lower than that of bumblebee pollination. Two types of pollen grains, namely round and fusiform pollen, were transported to a stigma by bumblebees and wind, but fusiform pollen contributed to wind pollination to a larger degree, especially in the marginal population. Our results suggest that wind pollination was enhanced by pollen dimorphism in the marginal population of A. gymnandrum, and wind pollination may provide reproductive assurance when bumblebee activity is unpredictable during range expansion, indicating that ambophily is stable in this species and shift in pollination system could be common when plants colonize new habitats.     

Seed size,pollination costs and angiosperm success

Summary Seed plants capture pollen before seeds are dispersed and abort unpollinated ovules. As a result, each seed is associated with an accessory cost that represents the costs of pollen capture and the costs of aborted ovules. Accessory costs may explain the minimum seed size among species, because these costs are likely to comprise a greater proportion of total reproductive allocation in species with smaller seeds. For very small propagules, the costs of pollination may not be worth the benefits, perhaps explaining the persistence of pteridophytic reproduction at small propagule sizes. The smallest angiosperm seeds are much smaller than the smallest gymnosperm seeds, both in the fossil record and in the modern flora. This suggests that angiosperms can produce pollinated ovules more cheaply than gymnosperms. Pollination becomes less efficient as a species decreases in abundance, and this loss of efficiency is greater for species with a higher accessory cost per seed. We propose that the greater reproductive efficiency of angiosperms when rare can explain why angiosperm-dominated floras were more speciose than the gymnosperm-dominated floras they replaced.     

Pollination thoroughness and maternal yield regulation in wild radish,Raphanus raphanistrum (Brassicaceae)

Summary Under conditions where resources are limited, there are often negative correlations between components of maternal yield, or between fruit and flower production. Pollination, in turn, may vary among individuals and influence total maternal expenditure. We examined the impact of variation in pollination thoroughness upon yield components and overall plant growth in wild radish (R. raphanistrum) plants grown in the greenhouse. Plants received different pollination treatments in which 0% to 100% of all flowers produced were hand-pollinated. Fruit set was increased by hand-pollination, but rarely exceeded 30%, even when more than 50% of the flowers were pollinated. Plants receiving more thorough pollination or having greater proportion fruit set produced significantly smaller seeds. Seed number per fruit was not influenced by pollination treatment. Mean values of yield components and interactions between components often varied among plants from different maternal families. Increasing pollination thoroughness also resulted in dramatic decreases in flower production. If male fitness is related to flower number, there may be a tradeoff between maternal fecundity and successful pollen export operating at the whole-plant level in this species.     

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。     

The smallest of all worlds: pollination networks

A pollination network may be either 2-mode, describing trophic and reproductive interactions between communities of flowering plants and pollinator species within a well-defined habitat, or 1-mode, describing interactions between either plants or pollinators. In a 1-mode pollinator network, two pollinator species are linked to each other if they both visit the same plant species, and vice versa for plants. Properties of 2-mode networks and their derived 1-mode networks are highly correlated and so are properties of 1-mode pollinator and 1-mode plant networks. Most network properties are scale-dependent, i.e. they are dependent upon network size. Pollination networks have the strongest small-world properties of any networks yet studied, i.e. all species are close to each other (short average path length) and species are highly clustered. Species in pollination networks are much more densely linked than species in traditional food webs, i.e. they have a higher density of links, a shorter distance between species, and species are more clustered.     

Invasive rats and recent colonist birds partially compensate for the loss of endemic New Zealand pollinators

Reported declines of pollinator populations around the world have led to increasing concerns about the consequences for pollination as a critical ecosystem function and service. Pollination could be maintained through compensation if remaining pollinators increase their contribution or if novel species are recruited as pollinators, but empirical evidence of this compensation is so far lacking. Using a natural experiment in New Zealand where endemic vertebrate pollinators still occur on one offshore island reserve despite their local extinction on the adjacent North Island, we investigated whether compensation could maintain pollination in the face of pollinator extinctions. We show that two recently arrived species in New Zealand, the invasive ship rat (Rattus rattus) and the recent colonist silvereye (Zosterops lateralis; a passerine bird), at least partly maintain pollination for three forest plant species in northern New Zealand, and without this compensation, these plants would be significantly more pollen-limited. This study provides empirical evidence that widespread non-native species can play an important role in maintaining ecosystem functions, a role that needs to be assessed when planning invasive species control or eradication programmes.     

The secret pollinators: an overview of moth pollination with a focus on Europe and North America

Pollination is a crucial plant–animal interaction in ecosystems, and moths (Lepidoptera) are a widespread and species-rich group of flower visitors. In this article, plant and moth species connected via pollination interactions were identified from the literature, and information on the relevance of moth pollination in various ecosystems, including agro-ecosystems, was compiled, particularly for Europe and North America. Overall, 227 moth–flower pollination interactions were found, including certain specialized relationships between plants and pollinating seed predators. Most of the interactions could be attributed to the moth families Noctuidae (90 interactions, 56 species) and Sphingidae (85 interactions, 32 species), and to the plant families Orchidaceae (109 interactions, 22 species) and Caryophyllaceae (59 interactions, 16 species). Limited information is available on the role of moth pollination in natural ecosystems (7 studies). In temperate agro-ecosystems, moths are most likely not essential to crop pollination, but they can contribute to the pollination of non-crop plants, which are crucial to maintaining biodiversity in these ecosystems. In general, the role of moths as pollinators appears to be underestimated because only a few studies on moth pollination are available, and long-term, ecosystem-scale research is necessary to address temporal fluctuations in their abundance and community composition.     

IS FLORAL SPECIALIZATION AN EVOLUTIONARY DEAD‐END? POLLINATION SYSTEM TRANSITIONS IN RUELLIA (ACANTHACEAE)

Pollination systems frequently reflect adaptations to particular groups of pollinators. Such systems are indicative of evolutionary specialization and have been important in angiosperm diversification. We studied the evolution of pollination systems in the large genus Ruellia. Phylogenetic analyses, morphological ordinations, ancestral state reconstructions, and a character mapping simulation were conducted to reveal key patterns in the direction and lability of floral characters associated with pollination. We found significant floral morphological differences among species that were generally associated with different groups of floral visitors. Floral evolution has been highly labile and also directional. Some specialized systems such as hawkmoth or bat pollination are likely evolutionary dead-ends. In contrast, specialized pollination by hummingbirds is clearly not a dead-end. We found evidence for multiple reverse transitions from presumed ancestral hummingbird pollination to more derived bee or insect pollination. These repeated origins of insect pollination from hummingbird-pollinated ancestors have not evolved without historical baggage. Flowers of insect-pollinated species derived from hummingbird-pollinated ancestors are morphologically more similar to hummingbird flowers than they are to other more distantly related insect-pollinated flowers. Finally, some pollinator switches were concomitant with changes in floral morphology that are associated with those pollinators. These observations are consistent with the hypothesis that some transitions have been adaptive in the evolution of Ruellia.     

Studies on flower longevity in Digitalis

The flowers of Digitalis purpurea respond to pollination by rapid corolla abscission without any loss of corolla turgor, nor any significant loss of corolla constituents, relative to the corollas of unpollinated flowers of a similar age. The corollas of unpollinated flowers too eventually abscise, 6 d after the stigma opens, however, they do so with only a minimal loss of fresh weight or corolla constituents. Pollination causes an increase in ethylene production detectable within 1 h. Increased ethylene production occurs initially only from the upper portion of the style, later from the lower portion, and lastly, between 23 and 48 h after pollination, from the ovary plus calyx. The pollination response can be induced by exogenous ethylene, the degree of weakening of the corolla abscission zone being dependent upon the concentration and duration of the exposure period and on the stage of flower development. The regulation of ethylene biosynthesis and its involvement in the control of pollination-induced corolla abscission are discussed.     

Are empidine dance flies major flower visitors in alpine environments? A case study in the Alps,France

Pollination is one of the most important ecosystem services and bees the most important pollinators. As a population decline of bees has been documented in numerous regions of the world, it is crucial to develop understanding on other possible pollinators. Here, we study the potential pollination impact of Diptera, and among them Empidinae, in an alpine environment, where the abundance of bees is naturally lower. Interactions between 19 entomophilous plants and their flower visitors were recorded in a subalpine meadow in the French Alps during six weeks. Visitation frequencies were used to build the flower–visitor network. Our results show that interactions between flies and plants are dominant; flies represent more than 60% of all visitors, with 54% of them being Empidinae. We especially found that flies, Empidinae and bees are the main visitors of 11, three and one plants, respectively. When considering both bees and Syrphidae together, six plants were more visited by Empidinae; when considering bees and Syrphidae separately, 10 plants were more visited by Empidinae than by bees or Syrphidae. The results support the idea that flies widely replace bees as main flower visitors at altitude, and among them the Empidinae might play a key role in pollination.     

ANT INHIBITION OF POLLEN FUNCTION: A POSSIBLE REASON WHY ANT POLLINATION IS RARE

Ant pollination systems are remarkably rare. We show that pollen exposed to ants for brief periods exhibits reduced viability, reduced percent germination, and shorter pollen tubes relative to control pollen. Pollination with ant-borne pollen also results in lower seed-set than pollination with untreated pollen. This disruption of pollination processes must have exerted a powerful selection pressure against the evolution ofant-pollination systems. It is suggested that the nestbuilding and brood-rearing habits of ants require that they secrete large amounts of antibiotics to combat pathogenic microorganisms. It is these secretions that disrupt pollen function. Bees and wasps exhibit very different nesting behavior, consequently there are no chemical barriers to their coevolving with flowers as pollinators.     

Ecological and Evolutionary Implications of Bird Pollination

This paper addresses the question of how, and under what ecologicalcircumstances, bird pollination will be optimal for a plant,and which or how many of the available nectar-feeding bird specieswill be optimal pollen vectors. Pollination by birds is energetically expensive for the plants,and should accur only when birds can mediate optimal patternsof pollen flow and seed set. Each nectar-feeding bird has potentialadvantages and disadvantages as a pollen vector, related toits size, morphology, and foraging behavior. Which availablebird is the optimal pollinator depends on the plant's growthhabit, spatial distribution, and breeding system. The variousadaptations shown by plants favoring one pollinator over anotherall revolve around the secretion of nectar and the manner ofpresenting it to the birds. However, other aspects of plantmorphology, physiology, ecology, or life cycle may affect theproduction and presentation of nectar, and influence plant-pollinatorcoevolution. Many question remain regarding the interrelationsbetween pollination and the total biology of the plant; birdpollination systems may prove fruitful in yielding meaningfulanswers.     

小毛茛(Ranunculus ternatus Thunb.)花粉流潜能初探

在自然居群中对小毛莨传粉机制与距离作了观测,并对开花后花粉萌发能力的变化作了研究,结果是：该种兼具虫媒或风媒传粉机制,以虫媒传粉为主;传粉距离多数局限于２ｍ以内,但不排除远距离传粉的可能性;体有发试验表明,该种花粉萌发率在开第一天甚低,开花后２４ｈ达到最高值。作者推测,小毛莨花粉以近距离散布为主,但具有远距离传播的潜能。     

Pollen limitation and variation in floral longevity in gynodioecious Potentilla tanacetifolia

Pollination limitation is common in flowering plants and is thought to be a factor driving the evolution of floral traits.The plasticity of floral longevity to pollination may be an adaptation of plants to pollen limitation.However,this adaptation is less critical in short-lived flowers.To evaluate pollen limitation and the plasticity of floral longevity to pollination in Potentilla tanacetifolia,a gynodioecious herb with short-lived flowers,we analyzed its breeding system,tested sex-differential pollen limitation,and compared variations in floral display size in natural populations in Duolun County,Inner Mongolia,China.Hand pollination experiments and pollinator exclusion treatments revealed that P tanacetifolia is self-compatible and non-autonomously apomictic and shows sex-differential pollen limitation.The plasticity of floral longevity to pollination was observed; the floral duration of female plants was prolonged by approximately 3-4 hours with pollination exclusion treatment.Moreover,the percentage of flowers displayed on female plants during pollination exclusion treatment was significantly higher than that during natural pollination.Under natural pollination conditions,the percentage of flowers displayed on female plants was significantly higher than on hermaphrodite plants.Furthermore,approximately 50％ of the pollen grains spread out of the anthers of hermaphrodite flowers within 2 h of anthesis; the number of pollen grains adhering to the stigmas of hermaphrodite flowers was significantly higher than that adhering to female flowers when flowers shed their petals.These results indicate that variation in floral longevity may be an adaptive strategy to pollination conditions for gynodioecious P tanacetifolia.     

小毛茛(Ranunculus ternatus Thunb.)花粉流潜能初探

在自然居群中对小毛茛传粉机制与距离作了观测,并对开花后花粉萌发能力的变化作了研究,结果是：该种兼具虫媒或风媒传粉机制,以虫媒传粉为主;传粉距离多数局限于２ｍ以内,但不排除远距离传粉的可能性;体外萌发试验表明,该种花粉萌发率在开花第一天甚低,开花后２４ｈ达到最高值。作者推测,小毛茛花粉以近距离散布为主,但具有远距离传播的潜能。     

Effectiveness of buzz pollination in Pedicularis chamissonis: significance of multiple visits by bumblebees

Pollination success of plants is highly susceptible to the frequency of visits and foraging behavior of pollinators. Pollination of the nectarless flowers of Pedicularis species depends on bumblebee workers collecting pollen by vibrating the anthers (buzz pollination). However, little is known about the efficiency of the pollination system. Foraging behavior, pollen removal from anthers and pollen deposition on stigmas of P. chamissonis were studied to assess the effectiveness of buzz pollination in an alpine snowbed population of northern Japan. Although bumblebees tended to visit most of the flowers open at a given time within inflorescences during a single visit, pollen removal rate at the first visit was about 20%, and buzzing period decreased with increasing number of previous visits, resulting in a decreasing proportion of pollen removed per visit as the number of visits increased. These trends enable plants to provide pollen for more pollinators. The number of pollen grains deposited on stigmas was not saturated during the first visit and increased with additional visits. Irrespective of weak self-compatibility, evidence of interference between self and outcross pollen was lacking for seed production. Therefore, buzz pollination in P. chamissonis acts as a mechanism that improves the chance of cross-pollination upon multiple visits if pollinator visitation is frequent.