Ornithophily in the trumpet creeper (Campsis radicans).

The diversification of hummingbirds (Trochilidae) has shaped the pollination strategies and floral trait evolution in at least 68 families of flowering plants in the Western Hemisphere. The trumpet creeper (Bignoniaceae) is the quintessential example of ornithophily in eastern North America. The mutualistic relationship between this orange-flowered liana and the ruby-throated hummingbird (Archilochus colubris) was illustrated as early as 1731. However, neither historical nor modern accounts accurately describe the feeding behavior of ruby-throats at trumpet creeper flowers or the floral adaptations for ornithophily. This paper explores their surprisingly immersive mode of foraging at trumpet creeper flowers and quantitatively assesses floral traits in two populations in the Ozark Mountains. The ruby-throat's bill is approximately one-third the length of the trumpet-shaped flowers, which counters the tendency for the corolla length of ornithophilous plants to match the bill length of their principal hummingbird pollinator. To access the nectary, ruby-throats grasp or cling to the ventral petal lobe of the corolla with their claws and thrust their head and upper body into the flower. This immersive "floral-diving" had not been formally documented among the 356 species of hummingbirds until now. The didynamous anthers and stigma are strategically positioned inside the corolla to brush the crown feathers when the ruby-throat inserts its head. A narrow stricture in the corolla, about a third of the way up, allows the bill and tongue of hummingbirds to pass while blocking bumblebees and carpenter bees from reaching the nectary. As a result, the abundant sucrose-rich floral nectar seems to be reserved for hummingbird pollinators.

The evolution of Ericaceae flowers and their pollination syndromes at a global scale.

PREMISE: Floral evolution in large clades is difficult to study not only because of the number of species involved, but also because they often are geographically widespread and include a diversity of outcrossing pollination systems. The cosmopolitan blueberry family (Ericaceae) is one such example, most notably pollinated by bees and multiple clades of nectarivorous birds. METHODS: We combined data on floral traits, pollination ecology, and geography with a comprehensive phylogeny to examine the structuring of floral diversity across pollination systems and continents. We focused on ornithophilous systems to test the hypothesis that some Old World Ericaceae were pollinated by now-extinct hummingbirds. RESULTS: Despite some support for floral differentiation at a continental scale, we found a large amount of variability within and among landmasses, due to both phylogenetic conservatism and parallel evolution. We found support for floral differentiation in anther and corolla traits across pollination systems, including among different ornithophilous systems. Corolla traits show inconclusive evidence that some Old World Ericaceae were pollinated by hummingbirds, while anther traits show stronger evidence. Some major shifts in floral traits are associated with changes in pollination system, but shifts within bee systems are likely also important. CONCLUSIONS: Studying the floral evolution of large, morphologically diverse, and widespread clades is feasible. We demonstrate that continent-specific radiations have led to widespread parallel evolution of floral morphology. We show that traits outside of the perianth may hold important clues to the ecological history of lineages.

Evolutionary disruption in the pollination system of Vanilla (Orchidaceae).

Pollination of the pantropical Vanilla has been linked to melittophily and food deception. Here we investigated the role of flower traits on the reproduction of Neotropical Vanilla. We also studied the evolution of pollination systems in order to understand the origin of production of flower resources and the diversification of pollinators in this orchid genus. Our study was founded on data of adaptations in flower morphology, production of resources, scent release, pollinators and breeding systems of Vanilla and presenting new data on reproductive biology of V. palmarum. Data on reproductive biology of Vanilla were mapped onto a phylogeny to address our queries on the evolution of pollination systems in this genus. Vanilla palmarum shows a mixed mating system, with its facultative autogamous flowers being pollinated by hummingbirds. Its yellow flowers are scentless and produces nectar. Mapping of the pollination system onto trees resulted in one origin for bird pollination and at least two origins for autogamy in Vanilla. Nectar secretion has a single origin in the Neotropical thick-leafed lineage. Bird pollination of Vanilla is shown for the first time. The origin of ornithophily within a bee-pollinated clade is supported by flower morphology. Floral transitions to ornithophily have been favoured by the occupation of a distinct niche from that of the other thick-leafed Vanilla species. Despite its specialized pollination, V. palmarum is autogamous. A mixed mating system can promote reproductive assurance in the case of a decline in pollinator populations, or in areas where pollinator services are irregular or absent.

Judge it by its shape: a pollinator-blind approach reveals convergence in petal shape and infers pollination modes in the genus Erythrina.

PREMISE: Pollinators are thought to exert selective pressures on plants, mediating the evolution of convergent floral shape often recognized as pollination syndromes. However, little is known about the accuracy of using petal shape for inferring convergence in pollination mode without a priori pollination information. Here we studied the genus Erythrina L. as a test case to assess whether ornithophyllous pollination modes (hummingbirds, passerines, sunbirds, or mixed pollination) can be inferred based on the evolutionary analysis of petal shape. METHODS: We characterized the two-dimensional dissected shape of standard, keel, and wing petals from 106 Erythrina species using geometric morphometrics and reconstructed a phylogenetic tree of 83 Erythrina species based on plastid trnL-F and nuclear ribosomal ITS sequences. We then used two phylogenetic comparative methods based on Ornstein-Uhlenbeck models, SURFACE and l1OU, to infer distinct morphological groups using petal shape and identify instances of convergent evolution. The effectiveness of these methods was evaluated by comparing the groups inferred to known pollinators. RESULTS: We found significant petal shape differences between hummingbird- and passerine-pollinated Erythrina species. Our analyses also revealed that petal combinations generally provided better inferences of pollinator types than individual petals and that the method and optimization criterion can affect the results. CONCLUSIONS: We show that model-based approaches using petal shape can detect convergent evolution of floral shape and relatively accurately infer pollination modes in Erythrina. The inference power of the keel petals argues for a deeper investigation of their role in the pollination biology of Erythrina and other bird-pollinated legumes.

Evolution of Bird and Insect Flower Traits in Fritillaria L. (Liliaceae).

Pollinators are often perceived as a primary selective agent influencing flower traits such as colour, size, and nectar properties. The genus Fritillaria L. (Liliaceae), comprising approximately 150 species, is described as generally insect pollinated. However, there are at least three exceptions: two hummingbird-pollinated North American species and one passerine-pollinated Asian species. Despite this variation in pollination, little is known about flower traits that may accompany this shift in fritillaries. In this study, we aimed to assess the attractiveness of the floral traits for (new) pollinators and track the evolution of flowers traits in the context of a shift in the principal pollinator. Therefore, we studied 14 flower traits related to the pollination in 60 Fritillaria species and traced the evolutionary trajectory of these traits. We used a phylogenetic tree of the genus, based on five DNA markers (matK, rpl16, and rbcL, 18S, and ITS) to reconstruct the ancestral state of studied flower traits. The results show that in bird-pollinated species several new traits evolved. For example, flower colouration, nectar sugar, and amino acid concentration and composition fulfil the criteria of ornithophilous flowers, although flower traits do not exclude insect pollinators in bird-pollinated fritillaries. Interestingly, we recorded potential reversals from bird to insect pollination. Our analysis, showing a broad study of flower traits among closely related species in the context of pollinator shift, serves as a starting point for future work exploring the genetic and physiological mechanisms controlling flower traits in the genus Fritillaria.

Pollinators drive floral evolution in an Atlantic Forest genus.

Pollinators are important drivers of angiosperm diversification at both micro- and macroevolutionary scales. Both hummingbirds and bats pollinate the species-rich and morphologically diverse genus Vriesea across its distribution in the Brazilian Atlantic Forest. Here, we (i) determine if floral traits predict functional groups of pollinators as documented, confirming the pollination syndromes in Vriesea and (ii) test if genetic structure in Vriesea is driven by geography (latitudinal and altitudinal heterogeneity) or ecology (pollination syndromes). We analysed 11 floral traits of 58 Vriesea species and performed a literature survey of Vriesea pollination biology. The genealogy of haplotypes was inferred and phylogenetic analyses were performed using chloroplast (rps16-trnk and matK) and nuclear (PHYC) molecular markers. Floral traits accurately predict functional groups of pollinators in Vriesea. Genetic groupings match the different pollination syndromes. Species with intermediate position were found between the groups, which share haplotypes and differ morphologically from the typical hummingbird- and bat-pollinated flowers of Vriesea. The phylogeny revealed moderately to well-supported clades which may be interpreted as species complexes. Our results suggest a role of pollinators driving ecological isolation in Vriesea clades. Incipient speciation and incomplete lineage sorting may explain the overall low genetic divergence within and among morphologically defined species, precluding the identification of clear species boundaries. The intermediate species with mixed floral types likely represent a window into shifts between pollinator syndromes. This study reports the morphological-genetic continuum that may be typical of ongoing pollinator-driven speciation in biodiversity hotspots.

A lever action hypothesis for pendulous hummingbird flowers: experimental evidence from a columbine.

BACKGROUND AND AIMS: Pendulous flowers (due to a flexible pedicel) are a common, convergent trait of hummingbird-pollinated flowers. However, the role of flexible pedicels remains uncertain despite several functional hypotheses. Here we present and test the 'lever action hypothesis': flexible pedicels allow pendulous flowers to move upwards from all sides, pushing the stigma and anthers against the underside of the feeding hummingbird regardless of which nectary is being visited. METHODS: To test whether this lever action increased pollination success, we wired emasculated flowers of serpentine columbine, Aquilegia eximia, to prevent levering and compared pollination success of immobilized flowers with emasculated unwired and wire controls. KEY RESULTS: Seed set was significantly lower in wire-immobilized flowers than unwired control and wire control flowers. Video analysis of visits to wire-immobilized and unwired flowers demonstrated that birds contacted the stigmas and anthers of immobilized flowers less often than those of flowers with flexible pedicels. CONCLUSIONS: We conclude that flexible pedicels permit the levering of reproductive structures onto a hovering bird. Hummingbirds, as uniquely large, hovering pollinators, differ from flies or bees which are too small to cause levering of flowers while hovering. Thus, flexible pedicels may be an adaptation to hummingbird pollination, in particular due to hummingbird size. We further speculate that this mechanism is effective only in radially symmetric flowers; in contrast, zygomorphic hummingbird-pollinated flowers are usually more or less horizontally oriented rather than having pendulous flowers and flexible pedicels.

Molecular detection of Trypanosoma (Kinetoplastida: Trypanosomatidae) in black flies (Diptera: Simuliidae) from Thailand.

Trypanosomes are parasitic flagellate protozoans that are important disease causing agents in humans and animals including economically significant livestock. Many blood-sucking insects are known to be vectors of trypanosomes but there is no data for the haematophagous black fly species in Asia. In this study, a molecular approach based on the small subunit ribosomal RNA (SSU rRNA) gene was used to detect trypanosomes in black flies from Thailand. A total of 470 wild-caught adult black flies representing nine morphological species were examined. Ten (2%) specimens of two ornithophilic black fly species, Simulium asakoae complex (n = 4) and S. chumpornense (n = 6), were positive for trypanosomes. The SSU rRNA sequences revealed that all trypanosome DNA found in black flies from Thailand is closely related to Trypanosoma avium with >99% sequence similarity. This is also supported by a phylogenetic analysis in which all trypanosomes from Thai black flies were resolved in the clade of T. avium. This is the first report for trypanosomes in Asian black flies and it is suspected that these insects are potential vectors of avian Trypanosoma.

Reproductive success of the Canarian Echium simplex (Boraginaceae) mediated by vertebrates and insects.

Oceanic island ecosystems favour the appearance of novel interactions as a consequence of their depauperate and disharmonic flora and fauna. We investigated Echium simplex, endemic to the Anaga Biosphere Reserve in NE Tenerife, Canary Islands, belongs to the Canarian bird-flower element. Along two flowering seasons, we studied the breeding system of E. simplex, identified the floral visitors and compared the pollination effectiveness of different animal guilds (insects versus vertebrates) by means of selective exclosures. E. simplex is self-compatible but selfing significantly reduced fruit set. The flowers were visited by five bird species (mostly Phylloscopus canariensis and Serinus canarius, but also Cyanistes teneriffae, Sylvia atricapilla and Sylvia melanocephala), a lizard species (Gallotia galloti) and over a hundred insect species (mainly hymenopterans and coleopterans). Flying insects increased fruit set whereas small flower dwellers (mostly beetles) decreased both fruit and seed set. Vertebrates had a negligible effect on reproductive success. We conclude that although the floral resources provided by E. simplex may be important to some vertebrate species, these do not appear to contribute to increase fitness of the plant, which was more dependent upon flying insects for fruit and seed set. We additionally found that plant reproductive structures are heavily damaged by feral goats, which threaten the maintenance of this Canarian endemic species.

Pollination effectiveness of opportunistic Galápagos birds compared to that of insects: From fruit set to seedling emergence.

PREMISE OF THE STUDY: Relying on floral traits to assess pollination systems has been shown to underestimate the ecological service that novel mutualisms can provide. Although vertebrates with opportunistic food habits are common on islands, usually feeding upon flowers of entomophilous species (ES), little is known about how effective they are as pollinators. In a previous study, we had reported that native insectivorous and frugivorous Galápagos birds commonly visit ES flowers, without assessing whether they act as pollinators. Here we investigate this by focusing on three typically ES (Cryptocarpus pyriformis, Waltheria ovata, Cordia lutea) and one mostly ornithophilous species (OS), Opuntia echios. METHODS: The quantitative component (QNC: the product of floral visit frequency and number of flowers contacted) and qualitative components (QLC: fruit and seed set, fruit length, and mass and proportion of seedling emergence) of pollination effectiveness of birds was compared with that of insects. KEY RESULTS: Birds were not quantitatively important pollinators compared to insects. However, selective exclusion experiments in the four plant species revealed that all qualitative components of fitness improved when both birds and insects visited the flowers. Our study is the first to confirm pollination effectiveness of ES by native opportunistic birds. CONCLUSIONS: The Galápagos pollination systems are probably more generalized than previous data suggested and, given that ES dominate the flora of this archipelago, we argue that, contrary to expectation, birds might have an important role in maintaining the reproductive success and diversity of plant communities.

The Manú Gradient as a study system for bird pollination.

BACKGROUND: This study establishes an altiudinal gradient, spanning from the highland Andes (2400 m) to lowland Amazon, as a productive region for the study of bird pollination in Southeastern Peru. The 'Manú Gradient' has a rich history of ornithological research, the published data and resources from which lay the groundwork for analyses of plant-bird interactions. In this preliminary expedition we documented 44 plants exhibting aspects of the bird pollination syndrome, and made field observations of hummingbird visits at three sites spanning the Manú Gradient: 2800 m (Wayqecha), 1400 m (San Pedro), and 400 m (Pantiacolla). Some of the documented plant taxa are underrepresented in the bird pollination literature and could be promising avenues for future analyses of their pollination biology. The Manú Gradient is currently the focus of a concerted, international effort to describe and study the birds in the region; we propose that this region of Southeastern Peru is a productive and perhaps underestimated system to gain insight into the ecology and evolution of bird pollination. NEW INFORMATION: Observations were made on 11, 19, and 14 putatively bird pollinated plant species found at the high-, mid- and low-elevation sites along the gradient, respectively. Hummingbirds visited 18 of these plant species, with some plant species being visited by multiple hummingbird species or the same hummingbird species on differing occasions. Morphometric data is presented for putatively bird-pollinated plants, along with bill measurements from hummingbirds captured at each of three sites. Voucher specimens from this study are deposited in the herbaria of the Universidad Nacional de Agraria de La Molina (MOL), Peru and the University of British Columbia (UBC), Canada. The specimens collected represent a 'snapshot' of the diversity of bird-pollinated flora as observed over 10 day sampling windows (per site) during the breeding season for hummingbirds of Manú .

Hummingbird pollination and the diversification of angiosperms: an old and successful association in Gesneriaceae.

The effects of specific functional groups of pollinators in the diversification of angiosperms are still to be elucidated. We investigated whether the pollination shifts or the specific association with hummingbirds affected the diversification of a highly diverse angiosperm lineage in the Neotropics. We reconstructed a phylogeny of 583 species from the Gesneriaceae family and detected diversification shifts through time, inferred the timing and amount of transitions among pollinator functional groups, and tested the association between hummingbird pollination and speciation and extinction rates. We identified a high frequency of pollinator transitions, including reversals to insect pollination. Diversification rates of the group increased through time since 25 Ma, coinciding with the evolution of hummingbird-adapted flowers and the arrival of hummingbirds in South America. We showed that plants pollinated by hummingbirds have a twofold higher speciation rate compared with plants pollinated by insects, and that transitions among functional groups of pollinators had little impact on the diversification process. We demonstrated that floral specialization on hummingbirds for pollination has triggered rapid diversification in the Gesneriaceae family since the Early Miocene, and that it represents one of the oldest identified plant-hummingbird associations. Biotic drivers of plant diversification in the Neotropics could be more related to this specific type of pollinator (hummingbirds) than to shifts among different functional groups of pollinators.

Is floral morphology a good predictor of floral visitors to Antirrhineae (snapdragons and relatives)?

The association between plants and flower visitors has been historically proposed as a main factor driving the evolutionary change of both flower and pollinator phenotypes. The considerable diversity in floral morphology within the tribe Antirrhineae has been traditionally related to pollinator types. We used empirical data on the flower visitors from 59 Antirrhineae taxa from the literature and our own field surveys, which provide an opportunity to test whether flower phenotypes are reliable predictors of visitors and pollinator niches. The degree of adjustment between eight key floral traits and actual visitors was explored by testing the predictive value of inferred pollinator syndromes (i.e. suites of floral traits that characterise groups of plant species related to pollination). Actual visitors and inferred pollinator niches (categorisation of visitors' association using a modularity algorithm) were also explored using Linear Discriminant Analysis (LDA). The bee pollinator niche is correctly classified for flowers with dull corolla colour, without nectar guides, as the most important predictor. Both predictive value and statistical classification prove useful in classifying Antirrhineae taxa and the bee pollinator niche, mostly as a consequence of the high proportion of genera and taxa with occluded corollas primarily visited by bees. Our predictive approach rendered a high Positive Predictive Value (PPV) of floral traits in the diagnosis of visitors/pollinator niches. In particular, a high PPV was found for bees as both visitors and forming pollinator niches. In addition, LDA showed that four pollinator niches are well defined based on floral traits. The large number of species visited by bees irrespective of pollinator syndromes leads us to hypothesise their generalist pollinator role, despite the phenotypically specialised flowers of Antirrhineae.

Temporal, but not spatial, changes in expression patterns of petal identity genes are associated with loss of papillate conical cells and the shift to bird pollination in Macaronesian Lotus (Leguminosae).

In the generally bee-pollinated genus Lotus a group of four species have evolved bird-pollinated flowers. The floral changes in these species include altered petal orientation, shape and texture. In Lotus these characters are associated with dorsiventral petal identity, suggesting that shifts in the expression of dorsal identity genes may be involved in the evolution of bird pollination. Of particular interest is Lotus japonicus CYCLOIDEA 2 (LjCYC2), known to determine the presence of papillate conical cells on the dorsal petal in L. japonicus. Bird-pollinated species are unusual in not having papillate conical cells on the dorsal petal. Using RT-PCR at various stages of flower development, we determined the timing of expression in all petal types for the three putative petal identity genes (CYC-like genes) in different species with contrasting floral morphology and pollination syndromes. In bird-pollinated species the dorsal identity gene, LjCYC2, is not expressed at the floral stage when papillate conical cells are normally differentiating in bee-pollinated species. In contrast, in bee-pollinated species, LjCYC2 is expressed during conical cell development. Changes in the timing of expression of the above two genes are associated with modifications in petal growth and lateralisation of the dorsal and ventral petals in the bird-pollinated species. This study indicates that changes in the timing, rather than spatial distribution, of expression likely contribute to the modifications of petal micromorphology and petal size during the transition from bee to bird pollination in Macaronesian Lotus species.

Ornithophily for the nonspecialist: Differential pollination efficiency of the Macaronesian island paleoendemic Navaea phoenicea (Malvaceae) by generalist passerines.

PREMISE OF THE STUDY: A bird pollination syndrome exists in the Canary Islands archipelago across independent plant lineages despite the absence of specialist birds. The pollination efficiency of current floral visitors remains unknown for many plant species despite this being a fundamental factor in testing hypotheses about the origin of the syndrome. Here, we studied the components of pollination efficiency in the paleoendemic Navaea phoenicea, a species exhibiting conspicuous anatomical modifications associated with bird pollination. METHODS: We measured the components of the pollination efficiency (PE) of species foraging on flowers. The measured quantitative components were visitation frequency patterns to plants and individual flowers. The qualitative components were the contributions to the fitness of male and female functions (pollen removal and deposition and fruit set). KEY RESULTS: Pollination by warbler species was highly efficient, but visit frequency was low; conversely, Canarian chiffchaffs had high visit frequency and low efficiency. Overall PE was almost 0 for blue tits due to disruptive behavior. We also found insects acting as nectar robbers. CONCLUSIONS: Pollination efficiency of three of the four bird species visiting flowers of Navaea phoenicea may be high enough to maintain selective pressure on floral traits of a relict pollination syndrome. The behavior of these birds plays a crucial role in their pollination efficiency. Perching, by generalist passerines when visiting N. phoenicea flowers, is the most efficient habit. The frequency and PE of insect visits calls into question their role as legitimate visitors.

Hybridization between pollination syndromes as an ecological and evolutionary resource.

In plants, pollination syndromes (the correlated presence of many features of relevance to pollination mode, for instance pollination by a particular animal clade) are a striking feature of plant biodiversity, providing great floral phenotypic diversity (Fenster et al. ). Adaptation to a particular animal pollinator provides an explanation for why recently diverged plants can have such extreme differentiation in floral form. One might expect such elaborate adaptations to provide a high degree of pollinator specificity and hence reproductive isolation, but there are many cases where substantial gene flow exists between extreme floral morphs (see Table 1), and the resulting hybrids may be highly fertile. This gene flow provides tremendous opportunities to study the genetics and biology of the pollination syndromes by providing intermediate forms and segregating genotypes. If it is true that pollination syndromes result from adaptation under strong selection, we will expect such flowers to be crucibles of natural selection. If strong selection for particular floral phenotypes can be shown, then this, when coupled with hybridization, will give us one of the most valuable of all experimental systems for evolutionary research: gene flow and selection in balance. In this issue of Molecular Ecology, the paper of Milano et al. () delivers this. It shows that in populations of the Ipomopsis aggregata complex, gene flow between pollination morphs is high and selection to stabilize those morphs is also high: a probable case of gene flow-selection balance.

Reproductive biology of a hummingbird-pollinated Billbergia: light influence on pollinator behaviour and specificity in a Brazilian semi-deciduous forest.

Ornithophily has evolved in parallel several times during evolution of angiosperms. Bird pollination is reported for 65 families, including Bromeliaceae. One of the most diverse bromeliad is Billbergia, which comprises species pollinated mainly by hummingbirds. Based on investigations on flowering phenology, morpho-anatomy, volume and concentration of nectar, pollinators and breeding system, this paper explores the reproductive biology and pollinator specificity of B. distachia in a mesophytic semi-deciduous forest of southeastern Brazil. The results have show that B. distachia is pollinated by a single species of hermit hummingbird, Phaethornis eurynome, which search for nectar produced by a septal nectary, where the secretory tissue is located above the placenta. The species is self-incompatible. The combination of pollinator specificity, due to long corolla tubes that exclude visitation of short-billed hummingbirds, complete self-incompatibility and non-territorial behaviour of pollinators, it is very important to reduce pollen loss and increase gene flow within population. Our results indicate that studies on pollination biology and reproduction are essential to understand the evolutionary history of pollination systems of plants since, at least in Billbergia, variation in the pollinator spectrum has been recorded for different habitats among Brazilian forests. Furthermore, according to our data, foraging of Phaethornis on flowers is independent of air temperature and humidity, while the main factor influencing hummingbird visitation is daylight. Considering current knowledge on climatic parameters influencing hummingbird foraging, pollination and reproductive biology of Neotropical flora and environment of the hermit hummingbird in tropical forests, new insights on plant-pollinator interaction are provided.

Convergence beyond flower morphology? Reproductive biology of hummingbird-pollinated plants in the Brazilian Cerrado.

Convergent reproductive traits in non-related plants may be the result of similar environmental conditions and/or specialised interactions with pollinators. Here, we documented the pollination and reproductive biology of Bionia coriacea (Fabaceae), Esterhazya splendida (Orobanchaceae) and Ananas ananassoides (Bromeliaceae) as case studies in the context of hummingbird pollination in Cerrado, the Neotropical savanna of Central South America. We combined our results with a survey of hummingbird pollination studies in the region to investigate the recently suggested association of hummingbird pollination and self-compatibility. Plant species studied here differed in their specialisation for ornithophily, from more generalist A. ananassoides to somewhat specialist B. coriacea and E. splendida. This continuum of specialisation in floral traits also translated into floral visitor composition. Amazilia fimbriata was the most frequent pollinator for all species, and the differences in floral display and nectar energy availability among plant species affect hummingbirds' behaviour. Most of the hummingbird-pollinated Cerrado plants (60.0%, n = 20), including those studied here, were self-incompatible, in contrast to other biomes in the Neotropics. Association to more generalist, often territorial, hummingbirds, and resulting reduced pollen flow in open savanna areas may explain predominance of self-incompatibility. But it is possible that mating system is more associated with the predominance of woody hummingbird plants in the Cerrado plant assemblage than to the pollination system itself.

Pollination ecology of two species of Elleanthus (Orchidaceae): novel mechanisms and underlying adaptations to hummingbird pollination.

Relationships among floral biology, floral micromorphology and pollinator behaviour in bird-pollinated orchids are important issues to understand the evolution of the huge flower diversity within Orchidaceae. We aimed to investigate floral mechanisms underlying the interaction with pollinators in two hummingbird-pollinated orchids occurring in the Atlantic forest. We assessed floral biology, nectar traits, nectary and column micromorphologies, breeding systems and pollinators. In both species, nectar is secreted by lip calli through spaces between the medial lamellar surfaces of epidermal cells. Such a form of floral nectar secretion has not been previously described. Both species present functional protandry and are self-compatible yet pollinator-dependent. Fruit set in hand-pollination experiments was more than twice that under natural conditions, evidencing pollen limitation. The absence of fruit set in interspecific crosses suggests the existence of post-pollination barriers between these sympatric co-flowering species. In Elleanthus brasiliensis, fruits resulting from cross-pollination and natural conditions were heavier than those resulting from self-pollination, suggesting advantages to cross-pollination. Hummingbirds pollinated both species, which share at least one pollinator species. Species differences in floral morphologies led to distinct pollination mechanisms. In E. brasiliensis, attachment of pollinarium to the hummingbird bill occurs through a lever apparatus formed by an appendage in the column, another novelty to our knowledge of orchid pollination. In E. crinipes, pollinarium attachment occurs by simple contact with the bill during insertion into the flower tube, which fits tightly around it. The novelties described here illustrate the overlooked richness in ecology and morphophysiology in Orchidaceae.

From dusk till dawn: nocturnal and diurnal pollination in the epiphyte Tillandsia heterophylla (Bromeliaceae).

In order to compare the effectiveness of diurnal and nocturnal pollinators, we studied the reproductive biology and pollinators of Tillandsia heterophylla E. Morren, an epiphytic tank bromeliad endemic to southeastern Mexico. Since anthesis in T. heterophylla is predominantly nocturnal but lasts until the following day, we hypothesised that this bromeliad would receive visits from both diurnal and nocturnal visitors, but that nocturnal visitors would be the most effective pollinators, since they arrive first to the receptive flower, and that bats would be the most frequent nocturnal visitors, given the characteristics of the nectar. Flowering of T. heterophylla began in May and lasted until July. The species is fully self-compatible, with an anthesis that lasts for ca. 15-16 h. Mean volume of nectar produced per flower was 82.21 µl, with a mean sugar concentration of 6.33%. The highest volume and concentration of nectar were found at 20:00 h, with a subsequent decline in both to almost zero over the following 12-h period. T. heterophylla has a generalist pollination system, since at least four different morphospecies of visitors pollinate its flowers: bats, moths, hummingbirds and bees. Most of the pollinating visits corresponded to bats and took place in the early evening, when stigma receptivity had already begun; making bats the probable pollinator on most occasions. However, diurnal pollinators may be important as a 'fail-safe' system by which to guarantee the pollination of T. heterophylla.