Reproductive systems and crossing potential in three species ofBulbophyllum (Orchidaceae) occurring in Brazilian ‘campo rupestre’ vegetation

Experimental self-, cross- and interspecific pollinations were carried out inBulbophyllum weddellii, B. involutum andB. ipanemense (Orchidaceae). The last two species are closely related, butB. weddellii is somewhat more distant. The three species are self-compatible, with pollination by a vector necessary for fruit formation. In all crossing types, high rates of fruit abortion and formation of seeds without embryos were observed, particularly in interspecific crosses that involvedB. weddellii. Crosses between the more closely relatedB. involutum andB. ipanemense produced fruit formation rates and seed viability similar to those obtained in intraspecific crosses. These results agree with current hypotheses that suggest that interspecific crossing rates reflect phylogenetic proximity. Examination of pollen tube growth and aborted fruits suggests that a series of factors may be involved in the high abortion rate for fruits and large proportion of seeds without embryos. The low interspecific fertility noted forB. weddellii andB. involutum is important in the maintenance of isolation between these species that are sympatric, flower in the same period and share the same pollinators.     

A supplementary contribution of ants in the pollination of an orchid, Epipactis thunbergii, usually pollinated by hover flies

It has been controversial how extensively ants contribute to pollination, and we evaluated the contribution of the Japanese carpenter ant, Camponotus japonicus, to the pollination of an orchid, Epipactis thunbergii. Two-year field studies revealed that (1) the ant workers foraged even in cool/cloudy conditions and accordingly visited orchid flowers more frequently (about 40% of all the visitors) than hover flies, the principle pollinators (10–20%), and that (2) the flower-visiting ants occasionally removed pollinia from the anther and then delivered pollen onto the stigmatic surface of other flowers, although self-pollination might frequently occur in the consecutive visits of flowers within an inflorescence. An artificial pollination experiment with pollinia which had been transferred to the ant integument showed that (3) the treated flowers produced as many fruits and seeds as control flowers. We concluded that C. japonicus workers could actually pollinate E. thunbergii flowers and their relative importance as pollinators appeared to be largely dependent on the abundance of flower-visiting workers or weather conditions during the flowering period, which mainly determined the availability of hover flies.     

Pollination of the orchidEpipactis thunbergii by syrphid flies (Diptera: Syrphidae)

The behavior of visitors to the flowers of the orchidEpipactis thunbergii was studied, with special attention to the role of the epichile in the pollination process. Only four species of syrphid flies legitimately pollinated the flower, among whichSphaerophoria macrogaster was regarded as the most effective pollinator. The movable epichile, possessing a furrow at its base, played a critical role in the pollination process: it threw the syrphid fly onto the stigmatic surface when both sides of the basal slanting surface of the furrow were presumably pressed in the direction of the hypochile by the fore (and middle) legs of the retreating syrphid fly. At this moment, the fly received a set of pollinia on the thorax.     

Roles of pollination and short-chain saturated fatty acids in flower senescence

Pollination induced an immediate increase in ethylene production in Dianthus caryophyllus and Petunia hybrida. In Cymbidium, a lag of several hours was observed. In all three species, pollination induced premature flower senescence. Treatment of the stigmatic surface with aminoethoxyvinylglycine prior to pollination effectively blocked the increase in ethylene production and alleviated the detrimental effect of pollination on flower life.In all three tested species, octanoic and decanoic acids, when applied to the stigmatic surface, had no effect on ethylene production and flower life. In isolated Cymbidium lips placed with their cut base in solutions containing these fatty acids, no effects on red colouration, ethylene production, and ethylene forming enzyme activity were observed. In addition, ethylene sensitivity of isolated lips was not affected. The putative regulatory role of short-chain saturated fatty acids in (pollination-induced) flower senescence is discussed.     

Pollination mechanism in southern Brazilian orchids which are exclusively or mainly pollinated by halictid bees

The pollination process is documented in three sympatric orchids found in Curitiba, Paraná State, southern Brazil. InCampylocentrum aromaticum (Epidendroideae: Angraeciinae) andPrescottia densiflora (Spiranthoideae: Prescotiinae) halictid bees act as main pollinators with minor contributions from other insects, such as Syrphid flies. Because of the pollinarium and column structure inCyclopogon diversifolius. (Spiranthoideae, Spiranthinae), halictid bees are the only insects capable of performing pollination. In the three studied species pollinarium removal and deposition are achieved by interaction between the column and bee's mouth parts. Morphological and ecological flower features in agreement with this pollination mode are discussed and pollination by halictid bees is suggested to occur in a number of South American orchids.     

Reproductive biology of twoPrunus species (Rosaceae) in the Northwest Iberian Peninsula

We studied the reproductive biology ofPrunus spinosa andPrunus mahaleb (Prunoideae, Rosaceae) in the northwest Iberian Peninsula. The two species flowered at the same time (peaking on March 9 and 11, respectively in 1990) but differ significantly in their fruit maturation times. Nectar volume peaked in the early morning in both species, and was ten times greater inP. spinosa than inP. mahaleb. Neither species shows apomixis, nor does fruit-set occur if pollinators are excluded. In both species self-pollination resulted in fewer fruits than open pollination. The principal pollinators belong to theApidae family (79% and 63% of visits toP. spinosa andP. mahaleb, respectively). Results are compared with those for other rosaceous plants with fleshy fruits.     

Nectar flow and pollinators' efficiency in two co-occurring species ofCapparis (Capparaceae) in Israel

Two closely related species ofCapparis, C. ovata andC. spinosa, which are exposed to the same pollination environment were studied. The nectar volume and concentration ofC. ovata are higher than inC. spinosa. Both species have similar pollination efficiency, but the relative contribution of each pollinator is different.C. ovata is pollinated mainly hy hawkmoths while the principal pollinators inC. spinosa are bees.     

The floral biology ofThelymitra epipactoides (Orchidaceae), and the implications of pollination by deceit on the survival of this rare orchid

Thelymitra epipactoides has a highly variable visual display achieved through polychromatic flowers and variable inflorescence size, bearing between 7 and 31 flowers, which attract foraging polylectic bees. Only bees of the genusNomia were observed carrying pollinia and successfully pollinating the orchid. The genusNomia contains polylectic, pollen gathering species that store pollen in both the crop and scopa on the hind legs. The absence of a reward for the bees indicates the orchid is relying on deception to attract visitors. The relationship of deception to mimicry is discussed. Once on the flower, tactile, visual and possibly olfactory stimuli direct bees to the false anther formed by the voluminous column wings, where morphological adaptations of the flower ensure that the pollinarium is deposited on the gaster of the bee to effect pollination. — The lack of seed set observed on the Victorian coast appears to be due to the absence of pollinators from the heath and grassland communities in which the orchid grows. This may well be a consequence of the reduced number of plants flowering in the community (a result of the elimination of fire at these sites), thus not maintaining a floral community attractive to potential pollinators.     

Contrasting breeding systems in twoEriotheca (Bombacaceae) species of the Brazilian cerrados

The pollination biology and breeding systems ofEriotheca pubescens andE. gracilipes have been studied. These two species occur as trees in cerrado vegetation, the neotropical savannas of Central Brazil, with partially sympatric distributions. They have similar phenology and floral structure, although the flowers ofE. pubescens are larger. Both species have nectar flowers pollinated by largeAnthophoridae bees but the main pollinators of each species differ in size. The species have markedly different breeding systems: late-acting self-incompatibility inE. gracilipes and apomixis stimulated by pollination inE. pubescens.     

Differentiation of floral color and odor in two fly pollinated species ofMetrodorea (Rutaceae) from Brazil

We investigated if differences in morphological characters in two species ofMetrodorea (Rutaceae) from Brazilian semideciduous forests correspond to some pollination divergence.M. nigra andM. stipularis are sympatric species, display a similar floral morphology, are protandrous, self-incompatible, their flower periods overlap, and both are pollinated by flies.M. nigra main pollinators arePseudoptiloleps nigripoda (Muscidae) andFannia sp. (Fanniidae);M. stipularis major pollinators arePhaenicia eximia (Calliphoridae),Palpada sp. andOrnidia obesa (Syrphidae). The distinct floral odor (disagreeable inM. nigra and sweet inM. stipularis) and color (brownish violet vs. pale yellow) determine the differences on type and number of floral visitors observed. Several species from semideciduous forests initially considered to be pollinated by diverse insects, present flies as main pollinators, stressing the importance of fly pollination in such habitats.     

Pollination genetics of hybridization in sympatric populations of asclepias exaltata and a. syriaca (asclepiadaceae)

Enzyme electrophoresis of pollinia and seeds was used to identify pollinia on pollinators, interspecific pollinations, and hybrid seed production in sympatric populations of Asclepias exaltata and A. syriaca. The frequency of mixed pollinia loads on pollinators was low. Only 4.1% (N= 169 pollinia) and 8% (N= 244 pollinia) of the pollinia collected from pollinators of A. syriaca and A. exaltata, respectively, were identified as pollinia from the other species. Natural levels of interspecific pollination, 3.6% (N = 166 pollinia) on A. syriaca and 3.1% (N = 228 pollinia) on A. exaltata, were typically lower than the number of foreign pollinia carried by pollinators. Hybrid seeds were identified in only two of 208 A. syriaca fruits and one of 178 A. exaltata fruits. Hybrid seeds were largely underdeveloped in the single A. exaltata fruit. High fruit set (34.7%) and near normal seed set following hand-pollination of A. syriaca with A. exaltata pollinia suggest that hybridization is more likely between these taxa when A. syriaca is the maternal parent. Our findings indicate that the likelihood of hybridization between A. exaltata and A. syriaca is remote. Nevertheless, introgressive hybridization has been documented in these species, which suggests that hybridization remains a strong evolutionary force even for species that infrequently interbreed.     

Pollination niche overlap between a parasitic plant and its host

Niche theory predicts that species which share resources should evolve strategies to minimise competition for those resources, or the less competitive species would be extirpated. Some plant species are constrained to co-occur, for example parasitic plants and their hosts, and may overlap in their pollination niche if they flower at the same time and attract the same pollinators. Using field observations and experiments between 1996 and 2006, we tested a series of hypotheses regarding pollination niche overlap between a specialist parasitic plant Orobanche elatior (Orobanchaceae) and its host Centaurea scabiosa (Asteraceae). These species flower more or less at the same time, with some year-to-year variation. The host is pollinated by a diverse range of insects, which vary in their effectiveness, whilst the parasite is pollinated by a single species of bumblebee, Bombus pascuorum, which is also an effective pollinator of the host plant. The two species therefore have partially overlapping pollination niches. These niches are not finely subdivided by differential pollen placement, or by diurnal segregation of the niches. We therefore found no evidence of character displacement within the pollination niches of these species, possibly because pollinators are not a limiting resource for these plants. Direct observation of pollinator movements, coupled with experimental manipulations of host plant inflorescence density, showed that Bombus pascuorum only rarely moves between inflorescences of the host and the parasite and therefore the presence of one plant is unlikely to be facilitating pollination in the other. This is the first detailed examination of pollination niche overlap in a plant parasite system and we suggest avenues for future research in relation to pollination and other shared interactions between parasitic plants and their hosts.     

Pollination ofDianthus gratianopolitanus (Caryophyllaceae)

Pollination ofDianthus gratianopolitanus was studied in a population of the Swiss Jura mountains. Pollinators of this plant species are reported here for the first time. The flowers were not only visited by butterflies as postulated in the literature, but also by diurnal hawkmoths (Macroglossum stellatarum) and by diurnal and nocturnal noctuid moths. — Nectar is sucrose-dominant, the sugar concentration is moderate but the amino acid concentration is high. Nectar characteristics correspond well with the syndrome ofLepidoptera-pollinated flowers. — Field observations and flower characters (colour, range of the calyx length) suggest thatDianthus gratianopolitanus is an intermediate species in the transition of butterfly to moth pollination. — Lack of reproductive success inDianthus gratianopolitanus can not be attributed to lack of suitable pollinators.     

Floral scent in dioeciousSalix (Salicaceae)—a cue determining the pollination system?

Floral scents of male and female inflorescences of three dioeciousSalix species were collected by head-space adsorption, and analysed by GC-MS. InSalix caprea andS. cinerea 1,4-dimethoxy benzene was the main compound, and male and female scents showed a high degree of resemblance. No dominant compound was found inS. repens and malefemale scent similarity was low. Floral scent inSalix is likely a strong orientation cue, guiding pollinators between male and female plants ensuring pollen transfer and pollination. We suggest that a high degree of male-female floral scent resemblance is coupled to a high degree of insect pollination. Floral scent does not promote reproductive isolation betweenS. caprea andS. cinerea.     

An invasive dandelion unilaterally reduces the reproduction of a native congener through competition for pollination

The impact of invasive alien species on native species is of increasing global concern. Invasive plants have various negative effects on natives through competition; however, relatively little is known about competition for pollination. The relationship between Japanese native dandelions (Taraxacum spp.) and invasive congeners may be a typical case of such an interaction. For example, native dandelions are being replaced by invasive congeners, especially in urban and suburban areas of Japan. To explain this phenomenon, we hypothesized that when natives are mixed with attractive invasives, natives may suffer from reduced seed set because invasives deprive natives of pollinators or because pollinators frequently move between species, resulting in interspecific pollen transfer. To test this hypothesis, we studied the effect of the invasive dandelion T. officinale on the pollination and seed set of the native T. japonicum using artificial arrays of monospecific and mixed-species plots as well as natural populations. Taraxacum officinale attracted more pollinator visits, perhaps because it produced more nectar than T. japonicum. The number of pollinator visits to T. japonicum was reduced when the congeners were grown together, and pollinators moved frequently between the two species. The proportion of seed set for T. japonicum was reduced in the presence of T. officinale in both artificial arrays and natural populations. These results support our hypothesis that interspecific competition for pollination plays an important role in the recent replacement of native dandelions by invasive congeners in Japan. Because invasive dandelions are apomicts, negative effects are incurred only by sexual natives. Thus, this system can be recognized as a rare case of interspecific interaction through pollination.     

Pollen-pistil interactions in Populus: β-galactosidase activity associated with pollen-tube growth in the crosses P. nigra x P. nigra and P. nigra x P. alba

Summary In order to understand the nature of interspecific barriers in Populus, we have explored pollen/pistil interactions in intra- and interspecific crosses Populus nigra x P. nigra and P. nigra x P. alba. The kinetics of pollen-tube growth demonstrated that P. nigra and P. alba pollen tubes have distinct behavioral patterns inside P. nigra pistils. P. alba pollen tubes exhibit an unique S-shaped growth curve and an arrested growth site near the sylodium. P. nigra pollen tubes exhibit two growth phases, in the stigmatic tissues and in the ovarian cavity respectively. P. nigra and P. alba curves diverge 5 h after controlled pollination and could be related to a change in the physiology of the P. nigra pollen tube, which shifts from an autotrophic to a heterotrophic type of nutrition. Protein analysis of pollinated stigmatic extracts (0,6 and 20 h after pollination) revealed qualitative and quantitative differences that are related to the presence of either P. nigra or P. alba pollen tubes inside the stigmatic tissues. Increasing numbers of protein bands were detectable from 0 to 20 h after pollination only in intraspecific cross. Glycoproteins were detected, and the differences observed were dependent of the cross. -Galactosidase activity was found in pollinated stigmas, but an increase in its activity (one isozyme of pHi 4.2) between 6 h and 20 h after pollination was detected only in the intraspecific cross. This enzyme could play a role in heterotrophic pollen-tube nitrition, and its activity could be the final result of a series of interactions started by the initial pollen-stigma dialog.     

The pollination biology of two species of Helicteres (Malvaceae) with different mechanisms of pollen deposition

Species of Helicteres are pollinated mainly by hummingbirds and bats. Most species pollinated by hummingbirds have a mechanism of depositing pollen on the top of the pollinator's head such as is shown in this work for Helicteres sacarolha. H. brevispira has an unusual mechanism of depositing pollen grains under the tail or on the abdomen of the hummingbirds. The top of the birds’ head may be considered an efficient place to transport pollen grains, because it is plain, easily accessible for deposition and donation of pollen and not easily accessible for grooming, while the tail is movable and inclined. Thus, H. brevispira pollinators may carry or transfer fewer amounts of pollen grains than H. sacarolha pollinators from one flower to another. If a large amount of pollen grains is lost, a higher quantity of flower or pollen has to be produced to guarantee reproductive success. Plants of H. brevispira set higher number of flowers and pollen grains per flower than H. sacarolha and have also higher rates of fruit and flower abortion. Thus, pollination efficiency of H. brevispira may be reached by high pollen and flower production. Flower change mechanism presented in this species may be also involved with the optimization of pollinator feeding and pollination efficiency.     

Positive effects of flower abundance and synchronous flowering on pollination success,and pollinia dispersal in rewardless Changnienia amoena (Orchidaceae)

Pollination success and pollen dispersal in natural populations depend on the spatial‐temporal variation of flower abundance. For plants that lack rewards for pollinators, pollination success is predicted to be negatively related to flower density and flowering synchrony. We investigated the relationships between pollination success and flower abundance and flowering synchrony, and estimated pollinia dispersal distance in a rewardless species, Changnienia amoena (Orchidaceae). The results obtained in the present study revealed that male pollination success was negatively influenced by population size but was positively affected by population density, whereas female pollination success was independent of both population size and density. Phenotypic analysis suggested that highly synchronous flowering was advantageous through total pollination success, which is in contrast to previous studies. These results indicate that pollination facilitation rather than competition for pollinator visits occurs in this rewardless plant. The median distance of pollinia dispersal was 11.5 m (mean distance = 17.5 m), which is comparable to that of other rewardless plants but longer than for rewarding plants. However, pollen transfer occured mainly within populations; pollen import was a rare event. Restricted gene flow by pollinia and seeds probably explains the previous population genetic reporting a high degree of genetic differentiation between populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 477–488.     

高山物种栗色鼠尾草(Salvia castanea Diels)访花昆虫多样性与传粉行为变化

唇形科鼠尾草属是世界性分布、物种多样性丰富的大类群,具有独特的传粉模式和多样化的生态类型及繁殖策略,以往对鼠尾草属的花结构和雄蕊杠杆的生态功能、雄蕊杠杆机制对传粉者空间变异的进化响应和表型选择等方面已有较深入的研究,但至今对分布于不同区系代表性物种的传粉者组成、访花行为和繁育系统特征仍知之甚少。对分布于喜马拉雅东段至横断山高海拔地区栗色鼠尾草的传粉生态、交配系统和繁殖特性进行了研究,分析了2014年至2016年的年际间、2014年晴天和阴雨天的传粉者组成和传粉行为变化,探讨了这些变化对繁殖成功的影响。研究结果表明：3年共发现栗色鼠尾草有9种访花昆虫,传粉者组成及其行为变化较为明显。2014年有桔尾熊蜂Bombus friseanus、灰熊蜂B.grahami、圣熊蜂B.religiosus和中华蜜蜂Apis cerana 4种有效传昆虫,2015年仅有桔尾熊蜂是有效传粉者,而2016年的有效传粉昆虫改变为灰熊蜂和圣熊蜂。栗色鼠尾草的盗蜜现象较为普遍,主要盗蜜昆虫为灰熊蜂和桔尾熊蜂。桔尾熊蜂访花行为的年际变化较大,受天气条件的影响明显,同时其有效传粉行为可能显著影响了灰熊蜂的盗蜜行为。栗色鼠尾草的繁育系统为专性异交,主要依靠传粉者进行授粉,缺少传粉者时低程度的主动自花授粉可为其提供繁殖保障,且没有花粉限制和近交衰退。研究揭示了在高海拔地区,多变的天气条件可能显著影响着鼠尾草属植物的传粉者种类组成、访花行为和传粉效率,进而影响植物的繁殖成效和种群稳定。有效传粉频率是保证栗色鼠尾草较高自然结实率的主要因素,在一定程度上,盗蜜强度对繁殖成功具有中性的影响。本研究结果为阐明高山鼠尾草物种的繁殖如何受气候环境变化的影响,以及保证繁殖成功的可能策略奠定基础。     

Looks matter: changes in flower form affect pollination effectiveness in a sexually deceptive orchid

Many species of the sexually deceptive genus Ophrys are characterized by insect‐like flowers. Their form has been traditionally considered to play an important role in pollinator attraction and manipulation. Yet, the evolution of the floral form remains insufficiently understood. We hypothesize that pollinator‐mediated selection is essential for driving floral form evolution in Ophrys, but that form components are being subjected to varying selection pressures depending on their role in mediating interactions with pollinators. By using the Eucera‐pollinated Ophrys leochroma as a model, our aim has been to assess whether and in what manner pollination effectiveness is altered by experimental manipulation of the flower form. Our results show that floral form plays an essential and, so far, underestimated role in ensuring effective pollination by mechanically guiding pollinators towards the reproductive structures of the flower. Pollinators are significantly less effective in interacting with flowers having forms altered to resemble those of species pollinated by different hymenopteran genera. Further, those components used by pollinators as gripping points were found to be more effective in ensuring pollinia transfer than those with which pollinators do not directly interact. Thus, mechanically active and inactive components appear to be under different selection pressures. As a consequence, mechanically active components of the flower form could reflect adaptations to the interaction with particular pollinator groups, whereas mechanically inactive components can vary more freely. Disentangling selection patterns between the functionally different components of flower form may provide valuable insights into the mechanisms driving the morphological diversification of sexually deceptive pollination systems.