Are pollination syndromes useful predictors of floral visitors in Tasmania?

Abstract Diurnal visitors to the flowers of many native plant species were identified in a wide range of Tasmanian sclerophyllous vegetation between September 1996 and April 1997. These foraging profiles were analysed to determine whether they were characteristic of various floral morphologies in predictable ways. It was found that although visitor profiles were sometimes consistent with classic pollination syndromes, these syndromes were unreliable predictors of floral visitors. Very few flowers were exclusively bird‐pollinated, and none were strictly fly‐, beetle‐, wasp‐, or butterfly‐pollinated. The majority of flowering plants were unspecialized in their morphology, and consequently hosted a diverse array of visitors. In addition, visitor profiles to congeners with similar floral morphologies, and even to conspecifics, differed between habitats. Altitude was a major factor in determining visitors, with flies being the most abundant visitors above 700 m. However, congeners in several genera of Epacridaceae, as well as the genus Correa, which differed in floral morphology also differed in visitor profiles. Tubular flowers were associated with birds, while flowers with more accessible nectar were visited by insects. The only taxa exhibiting a bee‐pollination syndrome that were largely visited by bees were the Fabaceae and Goodenia ovata Sm. Several species with purple or pink flowers were also predominantly visited by bees, but did not strictly conform to the melittophilous syndrome. In contrast, other flowers exhibiting an ostensibly mellitophilous syndrome hosted very few bees. Of these, species that occurred at high altitude were mainly visited by flies, while others received very few potential pollen vectors.     

Can pollination syndromes indicate ecological restoration success in tropical forests?

We evaluated the pollination syndromes of plant species occurring in revegetated patches of riparian Atlantic Forest in order to evaluate the success of restoration process. Between March 2013 and January 2014, the floral traits of all of the flowering plants found in, among four restoration sites of different ages and one reference site, were recorded and used to characterize pollination syndromes. Richness, abundance, and composition of pollination syndromes were related to season, age and width of the forest fragment, species richness and abundance of sampled plants, and also to the quality of the surrounding matrix. There were differences in the composition of syndromes among sampling units and among seasons. Richness and abundance of pollination syndromes varied among climatic periods, the highest values occurred at the end of the dry season and the start of the rainy season. Older, wider, and areas with more plants had higher values of richness and abundance of syndromes. The quality of the surrounding matrix influences only the richness of syndromes. It was concluded that floral traits are good indicators of ecological restoration of riparian forests and that the surrounding matrix contributes to the greater richness of syndromes. However, when planning for active restoration, attention should be given to the proper choice of plant species on the basis of pollination syndromes that should attract pollinators.     

Hooks for mammal pollination?

Summary Two species of Banksia (family Proteaceae) studied in Australia were shown to be pollinated by small, non-flying mammals rather than by birds as previously thought, and to possess several adaptations appropriate for mammal-rather than bird-pollination: odor, troughs that channel excess nectar to the ground for attraction, open inflorescence structure for nectar accessibility, hooked wiry styles for effective pollen transfer, crepuscular and nocturnal nectar and pollen presentation, and copious nectar. This apparently is the first documentation with quantified data of pollination by non-flying mammals, although many other probable examples exist.     

How to cheat when you cannot lie? Deceit pollination in Begonia gracilis

Mimicry between rewarding and non-rewarding flowers within individuals has been accepted as a strategy favored by selection to deceive pollinators. It has been proposed that this mechanism relies on the exploitation of pollinator's sensory biases, but field evidence is still scarce. In this study, we describe the mechanism of deceit pollination in the monoecious herb Begonia gracilis, a species with exposed rewarding structures (pollen) and intersexual mimicry. Specifically, we test the role of mimicry and exploitation of sensory biases on the reproductive success of male (pollination visitation) and female flowers (probability of setting fruits). We show that pollinators' perception of the amount of reward provided by male flowers is influenced by the independent variation in the sizes of the androecium and the perianth. Large rewarding structures and small perianths were preferred by pollinators, suggesting a central role of the relative size of the rewarding structure on pollinators' foraging decisions. Hence, rewarding male flowers cheat pollinators by exploiting their sensory biases, a strategy followed by non-rewarding female flowers. We suggest that intersexual mimicry operates through the functional resemblance of male flowers' deceit strategy. Artificial manipulation of the flowers supports our findings in natural conditions. Overall, we propose that the continuous and independent variation in the size of the perianth and the reproductive organs among male and female flowers could itself be adaptive.     

Transfer of pollinaria on birds’ feet: a new pollination system in orchids

We report the discovery of a new mechanism of pollination in orchids: transfer of pollinaria on the feet of birds. Observations carried out in South Africa and Malawi showed that the orchids Disa chrysostachya Sw. and Disa satyriopsis Kraenzl. are pollinated by sunbirds. Pollinaria of these orchids become attached firmly to the birds toes when they perch on the tall narrow inflorescences which are packed tightly with numerous small orange flowers. Birds typically perch on the lower part of an inflorescence while reaching up to feed on nectar in flowers on the upper part, but occasionally reverse this position to probe the lower flowers. The nectar is contained within a short bulbous spur with a narrow entrance that permits entrance of a sunbirds slender tongue. Contrary to expectation, the pollination mechanism in D. chrysostachya is remarkably efficient with about 6.1% of pollen reaching stigmas on other plants and fruit set occurring in 95% of flowers at one site. Birds seldom move their feet once perched, thus minimizing the incidence of self-pollination, either within or between flowers on an inflorescence.     

First report on generalized pollination systems in Melastomataceae for the Andean páramos

Melastomataceae is a megadiverse family with records of transitions from specialized to generalized pollination systems for several species. These transitions are associated with the colonization of new, unpredictable and/or impoverished pollinator habitats or habitats where specialized pollinators are scarce (e.g., in highland environments). The bee species diversity is low in highlands. Therefore, autonomous breeding systems such as apomixis and self-pollination emerge in these environments. In this paper, we studied the floral traits associated with the generalization of pollination systems and registered the floral visitors of two species in the Colombian Andes: Miconia cataractae and M. elaeoides. We investigated the breeding system of M. elaeoides. Both species presented small flowers, short anthers of medium pore size, and nectar-producing stomata on the base of the anthers. Miconia cataractae produced an average of 1.62 μl nectar/flower, a sugar concentration of 6.78%, whereas M. elaeoides produced 0.09 μl nectar/flower, a sugar concentration of 6.13%. We recorded a wide diversity of pollinators for both species, mainly insects from the orders Hymenoptera and Diptera. Miconia elaeoides presented a mixed breeding system and was also capable of setting fruits by apomixis. We conclude that flower and anther morphology, combined with nectar production, thus represent convergent traits resulting in a generalist pollination system shared by M. cataractae and M. elaeoides. Here, we presented the first generalist pollination system recorded for Miconia (and the Melastomataceae) in the Andes, the first report for a species from the small-pored section Amblyarrhena, and the first report for a species from the large-pored section Cremanium in Colombia.     

Specialized pollination by honeybees in Cymbidium dayanum,a fall–winter flowering orchid

Floral biology and pollination mechanisms of Cymbidium dayanum, an endangered epiphytic orchid, were investigated in south Kyushu, Japan. The flowering period spanned approximately 4 months from fall to winter, with the inflorescences often blooming asynchronously on each plant and individual flowers commonly lasting for a month. The nectarless flowers are self-compatible but cannot autonomously self-pollinate; the orchid needs to attract pollinators by deceit for capsule production. The field observations showed that the flowers were pollinated exclusively by the Japanese honeybee Apis cerana japonica, despite its long flowering period. The worker bees pollinated flowers and/or received the pollinarium on the thorax, while escaping from the labellum chamber. The natural fruit-set ratios at the population level, an estimate of pollination success, varied interannually but were generally low, as the result of infrequent flower visits by honeybee workers owing to the cold winter climate and the lack of a nectar reward. Because most flowers that were artificially pollinated in the winter successfully developed into capsules, the coldness was not considered a direct cause of the low fruit-set ratios. Our results explicitly indicate that the bee pollination niche could be available to temperate plant species even during mid-winter. We inferred advantages for the winter flowering of C. dayanum.     

On ‘various contrivances’: pollination,phylogeny and flower form in the Solanaceae

Members of the euasterid angiosperm family Solanaceae have been characterized as remarkably diverse in terms of flower morphology and pollinator type. In order to test the relative contribution of phylogeny to the pattern of distribution of floral characters related to pollination, flower form and pollinators have been mapped onto a molecular phylogeny of the family. Bilateral flower symmetry (zygomorphy) is prevalent in the basal grades of the family, and more derived clades have flowers that are largely radially symmetric, with some parallel evolution of floral bilateralism. Pollinator types (‘syndromes’) are extremely homoplastic in the family, but members of subfamily Solanoideae are exceptional in being largely bee pollinated. Pollinator relationships in those genera where they have been investigated more fully are not as specific as flower morphology and the classical pollinator syndrome models might suggest, and more detailed studies in some particularly variable genera, such as Iochroma and Nicotiana, are key to understanding the role of pollinators in floral evolution and adaptive radiation in the family. More studies of pollinators in the field are a priority.     

Wind or insect pollination? Ambophily in a subtropical gymnosperm Gnetum parvifolium (Gnetales)

Gnetum (Gnetales) has long been regarded as insect pollinated due to its range‐restricted distribution in tropical rain forests, where wind pollination is supposed to be detrimental. However, ubiquitous pollen limitation in the tropics might cause transition to anemophily, or even ambophily for reproductive assurance, especially for gymnosperms such as Gnetum, which exhibit various anemophilous syndromes, including absence of petals, greenish color of strobili, dioecy and uniovulate flowers. Pollination treatments applied to Gnetum parvifolium in southern China revealed this rare and endangered species to be pollen limited and incapable of apomixis. Pollen grains of G. parvifolium did not adhere to each other and could be trapped by interception traps near the male and female strobili. Seed set in the netted treatment (anemophily) was significantly higher than in the bagged treatment (apomixis) but lower than open pollination (anemophily and entomophily), indicating that both wind and biotic pollination contributed to seed production of G. parvifolium. The occurrence of ambophily in Gnetum and the prevalence of anemophily in Ehpedra and Welwitschia suggest that wind may also play a role in the pollination of the ancient Gnetales.     

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.     

Honeybee‐assisted wind pollination in bamboo Phyllostachys nidularia (Bambusoideae: Poaceae)?

Floral syndromes and pollination of three species of Phyllostachys bamboos were studied in Central China in 1999 and 2000. All were protogynous. Stigmas were receptive and had pollen deposited on them 2 days before anther dehiscence. The period of anthesis in the three bamboos was 3 days. Individual pollen grains of the three species were similar in size (30–40 μm in diameter) and had features typical of wind-pollinated plants. The ratios of pollen to ovules (p/o ratio) in P . nidularia , P . heteroclada and P . nuda were 6500, 12 700 and 33 000, respectively. Mean pollen loads on each flower (one ovule) of these three species were 7.3, 8.8 and 9.4 grains, respectively. Pollen transfer in P . heteroclada and P . nuda depended on wind, and no flower visitors were seen in the field. However, in P . nidularia , Apis cerana Fab. was a frequent pollen collector observed from 1200 to 1330 h. The visits undertaken by thousands of honeybees resulted in a large number of pollen grains being released from the anthers in a short time (10–15 min) in one day, which accelerated and synchronized the release of pollen from the anthers that seemed to enhance the chance of pollination. Given that honeybees played an indirect role in pollen transfer this could partly explain the low p/o ratio in P . nidularia . Reviewing the literature, we found insect visits to flowers of bamboos were not infrequent phenomena. We suggest pollination efficiency should be considered as one selective factor in attempts to understand mast flowering in bamboo. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 138 , 1–7.     

Did pollination shifts drive diversification in southern African Gladiolus? Evaluating the model of pollinator-driven speciation

The pollinator-driven ecological speciation model has frequently been invoked to explain plant richness in biodiversity hotspots. Here, by focusing on Gladiolus (260 species), a flagship example of a clade with diverse pollination biology, we test the hypothesis that high species diversity in southern Africa, one of the world's most floristically rich regions, has primarily been driven by ecological shifts in pollination systems. We use phylogenetic methods to estimate rates of transition between the seven highly specialized pollination strategies in Gladiolus. We find that pollination systems have evolved multiple times and that some pollination strategies arose by a variety of evolutionary pathways. Pollination shifts account for up to one-third of all lineage splitting events in the genus, providing partial support for the pollinator-driven speciation model. Transitions from the ancestral pollination mode to derived systems have also resulted in increased rates of diversification, suggesting that certain pollination systems may speed up speciation processes, independently of pollination shifts per se. This study suggests that frequent pollination shifts have played a role in driving high phenotypic and species diversity but indicates that additional factors need to be invoked to account for the spectacular diversification in southern African Gladiolus.     

How do visitation patterns vary among pollinators in relation to floral display and floral design in a generalist pollination system?

Diverse pollinator assemblages may impose complex selection and thus limit specialisation to particular pollinators. Previous work has concentrated on how visitation rates of different pollinators vary in space and time and how pollinators may vary in efficiency. In this study I quantify variation in visitation rates and foraging behaviour of different insect types (1) in space and time and (2) in relation to variation in floral design (flower size and form) and floral display (number of open flowers) for the distylous clonal shrub Jasminum fruticans. Mean visitation rate showed a significant interaction between insect type and population for seven populations in one year, and between insect types and years for a single population over 3 years. There was also a significant interaction between insect type and population for the proportion of flowers visited. In general the number of visits was positively related to the number of open flowers in a patch, but analyses by insect type showed that this was only true for bee flies and butterflies. Short-tongued bees showed a positive relationship between visitation rate and the number of open flowers on the focal stem, and hawkmoths and butterflies made more visits to plants with larger flowers. Hawkmoths were the only insect type to show a positive relation between the number of flowers visited per foraging bout and flower size. The significant differences between different insect types in patterns of variation in visitation rates in response to floral design and display may act to diversify selection on floral traits, and thereby constrain specialisation of the plant to particular pollinators.     

Reflexed flowers in Aeschynomene amorphoides (Fabaceae: Faboideae): a mechanism promoting pollination specialization?

This study aims to understand the role of floral traits in determining the reproductive biology of the leguminous shrub Aeschynomene amorphoides, endemic to western Mexico, which has unusually orientated flowers. We investigated the floral biology, pollination and breeding system based on a combination of morphological studies and field experiments, using controlled pollinations in a natural environment. The architecture and reflexed position of A. amorphoides flowers facilitate precise placement of pollen on the body of the pollinator, but this has a cost to A. amorphoides in terms of available flower resources. These costs to reproduction success are set against the attraction of a specialized pollinator, Tetraloniella jaliscoensis, which is capable of manipulating this unique pollination system in papilionoid (or flag) flowers. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 657–666.     

Calcineurin B-like interacting protein kinase OsCIPK23 functions in pollination and drought stress responses in rice （Oryza sativa L.）

Droughtis very harmful to grain yield due to its adverse effect on reproduction,especially on pollination proeess in rice.However,the molecular basis of such an effect still remains largely unknown.Here,wereport the role of amember of CBL(Calcineurin B-Like)Interacting Protein Kinase(CIPK)family,OsCIPK23,in pollination and stress responses in dee.Molecular analyses revealed that it is mainly expressed in pistil and anther but up-regulated by pollination,as well as by treatments of various abiotic stresses and phytohormones.RNA interference-mediated suppression of OsCIPK23 expression significantly reduced seed set and conferred a hypersensitive response to drought stress,indicating its possible roles in pollination and drought stress.In consistent,overexpression of OsCIPK23 induced the expression of seVeral drought tolerance related genes.Taken together,these results indicate that OsCIPK23 is a multistress induced gene and likely mediatesa signaling pathway commonly shared by both pollination and drought stress responses in rice.     

Buzziness as usual? Questioning the global pollination crisis

Concerns have been raised that invertebrate pollinators of crops and wild plants are in decline as a result of modern agricultural practices, habitat degradation, and introduced pests and diseases. This has led to demands for a response by land managers, conservationists and political decision makers to the impending 'global pollinator crisis'. In questioning this crisis, it becomes apparent that perceptions of a pollinator crisis are driven mainly by reported declines of crop-pollinating honeybees in North America, and bumblebees and butterflies in Europe, whereas native pollinator communities elsewhere show mixed responses to environmental change. Additionally, few staple food crops depend on pollinator services, and most crops that do are grown at small scales in diversified agro-ecosystems that are likely to support healthy pollinator communities, or in highly managed systems that are largely independent of wild pollinators. Consequently, justifying conservation action on the basis of deteriorating pollinator services might be misplaced. Nevertheless, existing initiatives to monitor pollinators are well founded, given the uncertainty about the dynamics of pollinator populations.     

When can two plant species facilitate each other's pollination?

Facilitation occurs when an increase in the density of one species causes an increase in the population growth rate or the density of a second species. In plants, ample evidence demonstrates that one species can facilitate another by ameliorating abiotic conditions, but the hypothesis that pollination facilitation – in which the presence of one flowering species increases pollinator visits to a second species – can also occur remains controversial. To identify the necessary conditions for pollination facilitation to occur, we constructed population models of two plant species that share the same pollinator and compete for establishment sites, and we assumed that heterospecific pollen can interfere with successful seed set. We found that facilitation for pollination occurs only when the pollinator visitation rate is an initially accelerating function of the combined numbers of flowering plants of both species in a patch. The presence of a second species can allow populations of a focal species either to persist for a longer amount of time before going extinct ("weak facilitation") or to persist indefinitely at a stable equilibrium density ("strong facilitation"). When only a single plant of either species can occupy a site, the plant species with the higher initial density can experience strong facilitation but will eventually out-compete the other species. However, when site occupancy was not exclusive, strong facilitation sometimes led to coexistence of the two species. Increasing the extent of pollen carryover increased the range of initial population densities leading to strong facilitation. In light of our theoretical results, we discuss the apparent rarity of pollination facilitation in nature.