腐生植物无叶美冠兰食源性欺骗传粉研究

无叶美冠兰是一种典型的腐生兰科植物,为揭示该物种的自然传粉机制,拓展对兰科植物生殖特性的认识,在广西雅长兰科植物国家级自然保护区对其开展了传粉生态学观测研究。结果表明:无叶美冠兰花朵具备高度自交亲和能力,但不存在自动自花授粉机制,必须依赖外部传粉媒介把花粉送到柱头,实现有效传粉;绿彩带蜂是无叶美冠兰唯一有效传粉昆虫;传粉昆虫与花朵在与传粉功能相关的关键性状在形态上良好拟合;绿彩带蜂的访花活动主要发生在3个阶段:8.6%发生在9:00~11:30,80.2%发生在11:30~14:00,11.2%发生在14:00~15:30;花朵在中午强烈的阳光直射下挥发出香甜的气味。无叶美冠兰花朵主要通过挥发极具诱惑力的香甜气味和唇瓣上黄色的蜜导来诱导绿彩带蜂进入花朵中觅食,传粉昆虫与花朵在与传粉功能相关的关键性状在形态上良好拟合促成有效传粉,绿彩带蜂在整个传粉过程没有获得报酬,是食源性欺骗传粉机制。     

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.     

Asian weaver ants,Oecophylla smaragdina,and their repelling of pollinators

The Asian weaver ant, Oecophylla smaragdina, is known to have outstanding predatory power. This ant can protect the host plants from attacks of phytophagous insects and therefore has been used for biological control in the tropics. We present evidence for a possible negative effect of Oecophylla on the performance of host plants. Our observation in a fruit orchard of rambutan in Sumatra suggested that the presence of Oecohylla nests on the trees statistically significantly lowered the flower-visiting rate of flying insects, involving the major pollinator Trigona minangkabau. The visiting rate of Oecophylla workers to each flower shoot of rambutan significantly negatively correlated with the visiting rate of flying insects. Empirical evidence of such an inhibitory effect on flower-visiting of pollinators cased by aggressive ants has been scarce so far.     

The unique pollination ofLeporella fimbriata (Orchidaceae): Pollination by pseudocopulating male ants (Myrmecia urens,Formicidae)

Leporella fimbriata is a self compatible orchid of southern Australia. It is dependant across its range on unique pollination by sexually attracted male winged antsMyrmecia urens, which pseudocopulate with the flower. Typical pollination sequences began with an initial circling then zig-zag flight to the flower. Vectors usually alighted on the inflorescence stem and quickly crawled to the flower where they adopted a copulatory position sideways along the wide labellum, pseudocopulatory probing immediately followed. In this position pollen carried on the thorax was deposited on the stigma. Departure from the labellum usually resulted in pollinium removal. Pollinator movements were restricted and the distribution leptokurtic with a mean of 3.141 ± 4.59 m. Pollination was widespread but variable from site to site and season to season with a maximum of 70% of all flowers being pollinated. Pollinator limitation is indicated. Traits essential for this pollination interaction include the coincidence of orchid and ant geographic distributions and the coincidence of flowering with the flight period of the ant. The production of pheromonelike substances and the distinctive floral morphology are also essential for attraction and manipulation of male ants. The ant mating system which the orchid can exploit is also important.     

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.     

Ant pollination of the palaeoendemic dioeciousBorderea pyrenaica (Dioscoreaceae)

The importance of ants for pollination in the dioeciousBorderea pyrenaica (Dioscoreaceae), a Tertiary palaeoendemic plant of the Pyrenees (NE Iberian Peninsula) was studied. The frequency of different visitors (ants, lady beetles, andDiptera) to staminate and pistillate flowers was quantified, and their effectiveness as pollinators was examined by means of fruit and seed set in selective experimental exclusions. Although ants were less abundant on flowers than other visitors, they were the most effective pollinators. Some qualitative factors of this mutualistic ant-plant interaction may account for their effectiveness: the small size of the ants, their high visitation rate to pistillate flowers, and the lack of reduction in viability of the pollen transported on the integument. In addition, the sedentary nature of ants assures their presence during the flowering period. The most abundant floral visitors ofB. pyrenaica were therefore not the most effective pollinators.     

Nectar parasitism of Asclepias syriaca by ants: Effect on nectar levels,pollinia insertion,pollinaria removal and pod production

Summary Milkweed (Asclepias syriaca L.) umbels and stems attended by ants (Lasius neoniger Emery and Tapinoma sessile (Say)) initiated significantly fewer pods and showed a trend to produce fewer mature pods than did umbels and stems not attended by ants. Since similar numbers of pollinia were inserted in ant-attended flowers, we hypothesize that ant-excluded flowers obtain more pollinia from other clones than do ant-attended flowers of this normally non-selfing species. If pollinators from other clones first visited flowers not depleted of nectar by ants, they could provide this source of foreign pollinia. Our experiments suggest that nocturnal noctuid and geometrid moths can provide these pollinia.     

A nocturnal Provespa wasp species as the probable pollinator of epiphytic orchid Coelogyne fimbriata

Many vespid wasps visit flowers to forage nectar. These hymenopterans sometimes contribute to flower pollination. However, none of the nocturnal wasp species is a known pollinator. We collected individuals of light‐attracted Provespa nocturna workers in a montane rainforest on Peninsular Malaysia: some wasps collected bore orchid pollinia on their thoraxes. Among 114 trapped individuals, four bore pollinaria and nine bore only viscidia, suggesting that pollinia had been successfully transported. Molecular barcoding of the pollinia (based on their ITS sequences) assigned the orchid to a species in Coelogyne fimbriata complex. These findings and our other analyses suggest that this nocturnal wasp contributes to pollination of an epiphytic nectarless orchid that probably releases olfactory attractants. This discovery sheds light on the importance of mutualistic relationships between the nocturnal social wasps and epiphytic orchids in Southeast Asian tropical rainforest canopies.     

Observations of the floral biology ofPrasophyllum odoratum (Orchidaceae,Spiranthoideae)

Prasophyllum odoratum is a vernal, nectariferous, terrestrial orchid that flowers profusely six to eight months following cyclical fires that disrupt sclerophyll woodlands. The morphology of the column and pollinarium is indicative of taxa placed within the subfam.Spiranthoideae. The orientation of the pollinaria to the stigma appears to prevent mechanical self-pollination. Both cross- and self-pollination appear to be effected by insects that forage within the brightly-colored, scented, non-resupinate flowers. Ants and drosophilid flies remove nectar, but do not appear to transport pollinaria between flowers. The primary pollinators are polytrophic flies in the fam.Syrphidae and opportunistic male bees in the genusLeioproctus (Colletidae). Approximately 52% of the flowers on a raceme set seed. The comparatively short floral tube ofP. odoratum reflects the dependence of this species on short-tongued insects to effect successful dispersal of pollinaria.     

Efficiency of herbivore exclusion by ants attracted to aphids on the vetch <Emphasis Type="Italic">Vicia angustifolia</Emphasis> L. (Leguminosae)

The efficiency of herbivore exclusion by ants on the vetch Vicia angustifolia L. (Leguminosae) with extrafloral nectary, mediated by ant attraction to aphids was investigated in a field census and laboratory experiments. In the field, workers of Lasius japonicus Santschi and Tetramorium tsushimae Emery frequently visited plants of the vetch parasitized by aphids of Aphis craccivora Koch, but only a few workers visited plants without aphids. An increase in the number of ants visiting a plant with increasing numbers of aphids caused a decrease in the number of larvae of the weevil, Hypera postica Gyllenhal. Therefore, the efficiency of herbivore exclusion by ants was higher on plants parasitized by Ap.craccivora aphids than that on plants unparasitized by aphids. In the laboratory experiments, L.japonicus workers frequently patrolled not only shoots with Ap.craccivora aphids but also shoots without them. However, T.tsushimae workers visited mainly shoots with Ap.craccivora aphids but less frequently on shoots without aphids. Therefore, L.japonicus workers excluded herbivores more efficiently on plants of the vetch than T.tsushimae workers. Consequently, the efficiency of herbivore exclusion by ants on the vetch can be influenced directly by differences in ant species and indirectly by the presence of aphids on plants. The present study highlights the significance of indirect interactions between ants and plants with extrafloral nectary, mediated by ant attraction to aphids for herbivore exclusion of plants.     

Deceptive pollination of the Lady's Slipper Cypripedium tibeticum (Orchidaceae)

To test whether the nectarless flowers of Cypripedium tibeticum attract pollinators through mimicry like the allied species C. macranthos var. rebunense, pollination biology of C. tibeticum was investigated in western China. Although C. tibeticum was also pollinated by bumble bee queens, i.e. Bombus lepidus , B. lucorum and B. hypnorum , no special, rewarding model plants were found in the habitat. Field experimentation confirmed that the flowers were self-compatible but insects were required to transfer orchid pollen to the stigma. Both Bombus queens and workers were visitors, but queens were much more frequent than workers and only queens were effective pollinators. Floral functional morphology analysis showed that it was large queens rather than small workers that fitted well with the flowers of C. tibeticum. With the faint sweet-fruity scent, the minor floral fragrance compound, ethyl acetate, probably plays a role in attracting bumble bees by food deception. The dark flowers with the inflated, trap-like labellum are hypothesized to mimic the nest site of queens. Therefore, bumble bee queens tend to be attracted by C. tibeticum through nest site mimic combined with food deception. Considering that the co-blooming flowers of C. flavum are pollinated by the Bombus workers, and C. smithii pollinated by a queen, we suggest that using the same bumblebees with different body sizes as the pollinators is the main reproductive isolation between interfertile C. tibeticum and C. flavum, while C. tibeticum and C. smithii tend to hybridize naturally.     

Lack of floral nectar reduces self-pollination in a fly-pollinated orchid

One explanation for the widespread absence of floral nectar in many orchids is that it causes pollinators to visit fewer flowers on a plant, and thus reduces self-pollination. This, in turn, could increase fitness by reducing inbreeding depression in progeny and promoting pollen export. The few previous investigations of this hypothesis have all involved bee-pollinated orchids and some have given contradictory results. We studied the effects of adding artificial nectar (sucrose solution) to the spurs of a non-rewarding long-proboscid fly-pollinated orchid, Disa pulchra. Addition of nectar significantly increased the number of flowers probed by flies (2.6-fold), the time spent on a flower (5.4-fold), the number of pollinia removed per inflorescence (4.8-fold) and the proportion of removed pollen involved in self-pollination (3.5-fold). The level of self-pollination increased dramatically with the number of flowers probed by flies. Experimental self-pollination resulted in fruits with only half as many viable seeds as those arising from cross-pollination. Pollinators were more likely to fly long distances (>40 cm) when departing from non-rewarding inflorescences than when departing from rewarding ones. These findings provide support for the idea that floral deception serves to reduce pollinator-mediated self-pollination.     

Effect of individual height and labellum colour on the pollination of Caladenia (syn. Arachnorchis) behrii (Orchidaceae) in the northern Adelaide region, South Australia

Caladenia behrii, a sexually deceptive orchid, is an endangered terrestrial orchid endemic to the Adelaide Hills, South Australia. We examined pollination success among individuals of different colours and heights in three populations of C. behrii in the northern Adelaide region. The labellum of C. behrii varies from cream to deep maroon. Over five years, the pollination success (pollinia deposited on stigma) of four colour groups (maroon, maroon and cream, hatched, and cream) was assessed for a total of 782 flowers. Labellum colour had no effect on the pollination success of individuals, indicating no frequency-dependent selection. It is likely that pollinators use the sexual pheromone mimic produced by the flowers as the main orientation cue. For three years the height of pollinated C. behrii individuals was recorded, along with the height of the nearest non-pollinated neighbour (distance of labellum from the ground, rather than stem length). Although a range of different heights was pollinated at population level, individual flowers that were taller than their closest neighbours were significantly more likely to be pollinated. Flower head height was not correlated with opening date and was greater for orchids growing among grass-tree leaves. Results imply that pollinators are more successful in finding tall flowers than short ones for visual and/or olfactory reasons; however, the effect of height preference is eliminated at population level.     

First confirmed case of pseudocopulation in terrestrial orchids of South America: Pollination of Geoblasta pennicillata (Orchidaceae) by Campsomeris bistrimacula (Hymenoptera, Scoliidae)

The attraction of male pollinating insects by sexual deception is known for several orchids from the Mediterranean, Australia, South Africa and South America. The sexual delusion may be so enticing in some species that it elicits males to attempt copulation with insect-like structures of the labellum. Pollination by such a pseudocopulation mechanism is reported here for the terrestrial orchid Geoblasta penicillata (Chloraeinae) from subtropical South America. Observations of the pollination process were carried out in two wild populations 560 km distant from each other. The only pollinators seen in both populations were male Campsomeris bistrimacula (Scoliidae) wasps. They attempted copulation with the insect-like labellum by directing the genitalia to its base whereby pollinia got attached to the dorsal surface of the metasoma. The present case of pseudocopulation, which is in South America the second known and the first recorded in wild populations, represents a striking parallel to the Australian Calochilus campestris also pollinated by male scoliid wasp of the genus Campsomeris.     

Catching ants with honey: an experimental test of distraction and satiation as alternative modes of escape from flower-damaging ants

According to the distraction hypothesis, extrafloral nectaries (EFN) evolved under selection to entice ants away from floral nectaries, reducing ant-mediated damage to flowers and/or interference with pollinators. Predator-satiation, through production of nectar in either surplus flowers or EFN, provides an alternative mechanism for reducing the impact of ants as flower visitors. I tested these two hypotheses by experimentally adding EFN to flowering plants of the alpine wildflower, Polemonium viscosum, and by surveying the relationship between ant visitation and nectary number in nature. Plants of P. viscosum lack EFN and experience flower damage by ants of Formica neorufibarbus gelida. Ant behavior was compared on plants with five flowers and three experimental EFN and on controls with equal floral display, but no EFN. Addition of EFN increased flower visitation by ants. The effect of EFN on flower visitation did not depend on proximity of EFN to flowers or attractiveness of EFN to ants. Findings suggest that ants perceived patch quality on a whole plant basis, rather than responding to EFN and flowers as distinct nectar patches. Ant visitation did not keep pace with nectary number in nature. The relationship between ant visitation and nectary number per plant was weak and shallow as predicted under satiation. Ant foraging choices on experimental inflorescences showed that ants bypass flowers avoided by earlier ants, enhancing probability of escape via satiation. Results do not support the idea that EFN evolve to reduce flower visitation by ants, but show instead that nectar in surplus flowers can satiate ants and reduce their negative impacts on flower function and integrity.     

Solitary invasive orchid bee outperforms co-occurring native bees to promote fruit set of an invasive Solanum

Our understanding of the effects of introduced invasive pollinators on plants has been exclusively drawn from studies on introduced social bees. One might expect, however, that the impacts of introduced solitary bees, with much lower population densities and fewer foragers, would be small. Yet little is known about the potential effects of naturalized solitary bees on the environment. We took advantage of the recent naturalization of an orchid bee, Euglossa viridissima, in southern Florida to study the effects of this solitary bee on reproduction of Solanum torvum, an invasive shrub. Flowers of S. torvum require specialized buzz pollination. Through timed floral visitor watches and two pollination treatments (control and pollen supplementation) at three forest edge and three open area sites, we found that the fruit set of S. torvum was pollen limited at the open sites where the native bees dominate, but was not pollen limited at the forest sites where the invasive orchid bees dominate. The orchid bee’s pollination efficiency was nearly double that of the native halictid bees, and was also slightly higher than that of the native carpenter bee. Experiments using small and large mesh cages (to deny or allow E. viridissima access, respectively) at one forest site indicated that when the orchid bee was excluded, the flowers set one-quarter as many fruit as when the bee was allowed access. The orchid bee was the most important pollinator of the weed at the forest sites, which could pose additional challenges to the management of this weed in the fragmented, endangered tropical hardwood forests in the region. This specialized invasive mutualism may promote populations of both the orchid bee and this noxious weed. Invasive solitary bees, particularly species that are specialized pollinators, appear to have more importance than has previously been recognized. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Autonomous self‐pollination in the nectarless orchid Pogonia minor

The pollination biology of the nectarless orchid Pogonia minor was investigated in central Japan. The investigation revealed that the solitary flowers failed to attract pollinators, while high rates of fruit set were observed in the natural population. Comparable levels of fruit set were obtained in bagged, artificial self‐pollinated and artificial cross‐pollinated plants, indicating that the species is not pollinator‐limited for fruit set under natural conditions. Autonomous self‐pollination in P. minor resulted from a reduced rostellum, which allowed contact between the pollinia and the stigma. Self‐pollination is thought to be an adaptive response that provides reproductive assurance under conditions of pollinator limitation. Since pollen limitation is generally known to be frequent among deceptive orchids, strong pollen limitation is probably a driving force in the autonomous self‐pollination mechanism in the nectarless orchid P. minor.     

Pollination by ants: consequences of the quantitative effects on a mutualistic system

Summary We have analysed the importance of worker ants (Proformica longiseta, Formicidae) as pollinators of a mass-flowering woody plant (Hormathophylla spinosa, Cruciferae) in the high-mountain area of the Sierra Nevada (southern Spain). We have quantified the abundance and foraging behavior of P. longiseta in comparison with winged flower visitors. We have also examined, by means of selective exclusion experiments, the role of ants as true pollinators, comparing them with the winged flower visitors. A total of 39 species belonging to 18 families visited the flowers of H. spinosa. All the visitors were winged insects, except P. longiseta, a species which alone made up more than 80% of the total number of insects found on the flowers. All pollinators of H. spinosa had similar foraging patterns, with 98% of total movements made between flowers within the same plant. Ants always made contact with the plant reproductive organs when foraging for nectar, and transferred large numbers of pollen grains. However, pollen exposed to ants for brief periods exhibited reduced percentage of germination. P. longiseta is both the most abundant and spatio-temporally predictable flower visitor of H. spinosa. These characteristics, weighted by their flower visitation rate, make worker ants the pollinator that maintains the strongest mutualistic interaction with H. spinosa. The exclusion experiments show that workers behave as true pollinators, since they contribute to increase the number of viable seeds produced by H. spinosa. The key factor of this interaction is mainly the great density of workers throughout the flowering period. In short, the H. spinosa-P. longiseta mutualistic interaction mainly depends on its high probability of occurrence.     

Intra‐floral resource partitioning between endemic and invasive flower visitors: consequences for pollinator effectiveness

1. Sympatric flower visitor species often partition nectar and pollen and thus affect each other's foraging pattern. Consequently, their pollination service may also be influenced by the presence of other flower visiting species. Ants are solely interested in nectar and frequent flower visitors of some plant species but usually provide no pollination service. Obligate flower visitors such as bees depend on both nectar and pollen and are often more effective pollinators. 2. In Hawaii, we studied the complex interactions between flowers of the endemic tree Metrosideros polymorpha (Myrtaceae) and both, endemic and introduced flower‐visiting insects. The former main‐pollinators of M. polymorpha were birds, which, however, became rare. We evaluated the pollinator effectiveness of endemic and invasive bees and whether it is affected by the type of resource collected and the presence of ants on flowers. 3. Ants were dominant nectar‐consumers that mostly depleted the nectar of visited inflorescences. Accordingly, the visitation frequency, duration, and consequently the pollinator effectiveness of nectar‐foraging honeybees (Apis mellifera) strongly decreased on ant‐visited flowers, whereas pollen‐collecting bees remained largely unaffected by ants. Overall, endemic bees (Hylaeus spp.) were ineffective pollinators. 4. The average net effect of ants on pollination of M. polymorpha was neutral, corresponding to a similar fruit set of ant‐visited and ant‐free inflorescences. 5. Our results suggest that invasive social hymenopterans that often have negative impacts on the Hawaiian flora and fauna may occasionally provide neutral (ants) or even beneficial net effects (honeybees), especially in the absence of native birds.     

Conflict resolution in an ant–plant interaction: Acacia constricta traits reduce ant costs to reproduction

Many plant species attract ants onto their foliage with food rewards or nesting space. However, ants can interfere with plant reproduction when they visit flowers. This study tests whether Acacia constricta separates visiting ant species temporally or spatially from newly opened inflorescences and pollinators. The diurnal activity patterns of ants and A. constricta pollinators peaked at different times of day, and the activity of pollinators followed the daily dehiscence of A. constricta inflorescences. In addition to being largely temporally separated, ants rarely visited open inflorescences. A floral ant repellent contributes to the spatial separation of ants and inflorescences. In a field experiment, ants of four species were given equal access to inflorescences in different developmental stages. On average, the frequency with which ants made initial, antennal contact with the floral stages did not differ, but ants significantly avoided secondary contact with newly opened inflorescences relative to buds and old inflorescences, and old inflorescences relative to buds. Ants also avoided contact with pollen alone, indicating that pollen is at least one source of the repellent. The results suggest A. constricta has effectively resolved the potential conflict between visiting ants and plant reproduction.