Nectar-mediated avian pollination in Cattleya (Orchidaceae: Laeliinae)

Orchids are notable for the variety of rewards produced for their pollinators. Nevertheless, many species are rewardless and pollinated by food-deceptive strategies. This is the case for Cattleya, a Neotropical genus of more than 100 species supposedly pollinated by food-deception. Here, I studied a member of the clade Sophronitis (Cattleya cernua) in forest areas of southeastern Brazil. The study included analyses of floral morphology, light microscopy of secretory tissues, histochemistry of flower resources, and measurements of nectar volume and concentration. Data on pollinators and mechanisms of pollination were collected in the field by means of film records, while breeding systems were studied using experimental treatments applied to cultivated specimens. The flower traits of Cattleya cernua show strong adaptation to avian pollination. Flowers produce 1-7 μl of a moderately concentrated nectar (17-50%). A secretory tissue at the distal portion of the cuniculus is responsible for nectar secretion. Secreted nectar is stored in the nectar chamber. Pollinaria deposition on the apex of bird beaks allows both short- and long-billed birds to pollinate the flowers. Plants from the studied population were fully self-compatible but pollinator-dependent. Pollinator frequency was higher than in food-deceptive Cattleya. As far as is known, this is the first record of nectar production in Cattleya. The discovery of a reward-producing species (C. cernua) within a genus entirely pollinated by food-deception strategies (Cattleya) provides clues and new insights into understanding the diversification of Laeliinae across the Neotropics.

Non-species-specific pollen transfer and double-reward production in euglossine-pollinated Vanilla

Commonly attributed to orchids, the pollen movement in Vanilla has been associated with food deception and specific plant-pollinator relationships. This study investigated the role of flower rewards and pollinator specificity in the pollen transfer of a widely distributed member to the euglossinophilous Vanilla clade, V. pompona Schiede using data collected from Brazilian populations. These included investigations on morphology, light microscopy and histochemistry, and analysis of flowers scent using GC-MS. The pollinators and the mechanisms of pollination were recorded through focal observations. The yellow flowers of V. pompona are fragrant and offer nectar as reward. The major volatile compound of the V. pompona scent, carvone oxide, shows convergent evolution in Eulaema-pollinated Angiosperms. The pollination system of V. pompona is not species-specific, but its flowers are strongly adapted to pollination by large Eulaema males. Pollination mechanism is based in a combination of perfume collection and nectar seeking. The dogma of a species-specific pollination system based on food deception in Vanilla has been broken with the increase in studies on this Pantropical orchid genus. Here, least three bee species and dual reward-offering are involved in pollen transfer in V. pompona. Visitation frequency of bees collecting perfumes, used in courtship by male euglossines, is higher than in searching for food, as short-lived young euglossine males seem to be more interested in sex than food. A pollination system based on offering both nectar and perfumes as resources is described for the first time in orchids.

Labellar Structure of the Maxillaria splendens Alliance (Orchidaceae: Maxillariinae) Indicates Floral Polyphenols as a Reward for Stingless Bees

Several studies have reported stingless Meliponini bees gathering hairs from the labella of Maxillaria spp., including M. ochroleuca, a member of the M. splendens alliance. Such hairs usually contain food materials and are thought to have nutritional value. The papillose labella of representatives of the Maxillaria splendens alliance, however, bear scattered, simple 1-5-celled uniseriate trichomes (hairs) that lack food materials. By contrast, here, as well as polyphenolic compounds, typical labellar papillae usually contain small quantities of starch, protein, and minute droplets of lipid, the last probably involved in the production of fragrance. Towards the labellum apex occur elevated groups of papillae that lack food materials, but contain volatile compounds, probably fragrance precursors. In the past, the terms 'trichomes' or 'hairs' and 'papillae' have been used interchangeably, causing some confusion. Since the trichomes, however, unlike the papillae, are easily detachable and can fragment, it is most likely they, not the papillae, that have previously been observed being collected by bees, but their poor food content indicates that they do not function as food-hairs. Even so, our field observations of M. ochroleuca reveal that stingless bees scrape polyphenol-rich labellar tissue and possibly use this material to produce a resinous, complex, heterogeneous substance commonly referred to as 'bee glue', used for nest construction and repair.

Evidence of floral rewards in Brasiliorchis supports the convergent evolution of food-hairs in Maxillariinae

PREMISE

Angiosperms distributed over a large geographical area may display considerable phenotypic variation that can be recognized at morphological and micromorphological levels. Here, we investigate the pollination biology and the presence of floral rewards in Brazilian populations of the widely distributed orchid, Brasiliorchis picta. Based on the new data presented here this study investigates the evolution of floral rewards in Maxillariinae, and tests for the occurrence of convergent evolution of food-hairs in this subtribe.

METHODS

Micromorphological and histochemical analyses of the labellar tissues were conducted, together with chemical analysis of fragrance and experiments involving the use of chemical baits. The evolution of floral rewards in Maxillariinae were addressed.

RESULTS

Microscopy revealed that B. picta offers food-hairs as a reward. Fragrance is produced by abaxially located labellar epidermal papillae. The main compound present in our samples (2-phenylethanol) also occurs in the aggregation pheromone produced by the mandible glands of pollinators, Meliponini bees. Our analyses indicate a high diversity of flower rewards and pollinators displayed by members of Maxillariinae, and support that edible trichomes evolved independently five times in the subtribe.

CONCLUSIONS

The high diversity of floral rewards and pollinators displayed by members of Maxillariinae suggests that different pollinator pressures are involved in the evolution of this neotropical subtribe. In addition, the offering of food-hairs, which are generally infrequently encountered in Orchidaceae, arose by convergent evolution in Maxillariinae.

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.

Unravelling the enigma of seed dispersal in Vanilla

Vanilla bean is the second most expensive spice in the world. While widely cultivated for centuries due to its importance for industry and gastronomy, its dispersers are unknown. In the present study, I investigated the system of seed dispersal of Neotropical vanillas based on experimental observations, the morpho-anatomy of fruits and seeds, and the effect of dormancy breakdown on seed germination. My results show the central cavity of the fruit contains copious amounts of seed with sclerified coats that are consumed by birds. The combination of gradually opening dehiscent fruits and a well-developed mesocarp rich in raphide idioblasts reinforces the idea that seed dispersal in Vanilla is more adapted to non-chewing animals. The digestive acids of birds sclerify the hard seed coats, breaking dormancy and promoting germination at the beginning of the wet season, which is fundamental for seedling survival and for the establishment of plants in the early stages of development during the rainy season. Zoochory in Vanilla is show for the first time. The chemical scarification of the seed coat is crucial for synchronizing the biological processes involved in seed germination. My evidence on endozoochory and the processes involved in seed germination of Neotropical vanillas provides new insights into understanding of the early evolution of seed dispersal in orchids.

So small and so rich: diversity of floral resources in miniature Oncidiinae (Orchidaceae) and their relation to pollinators

Oncidiinae is one of the most important subtribes among the Neotropical orchids, with an enormous diversity of floral morphology and secretory structures. This subtribe attracts a diverse array of pollinators which explore a variety of floral resources of its flowers. In this paper we provide a detailed investigation of the floral anatomy of 32 species of micro Oncidiinae. We applied histochemical tests in order to determine the diversity of the glands and rewards. The diversity of secretory flower structures and rewards was related to the group of pollinators known for this subtribe. We verified that half of the species (16 species, 50%) secrete oil as a resource, being pollinated by female of solitary bees. Species of some distinct nectar-secreting genera (four species, 12.5%) are pollinated by a range of nectar-searching animals. Species of the genus Notylia (four species, 12.5%) release floral perfumes that reward male Euglossini bees. Most of the investigated species (six species, 18.75%) possess osmophores that are involved in pollinator attraction. Two species of Capanemia (6.25%) do not offer any floral reward, suggesting that pollination by food deception is involved. There are strong variations in the anatomy of reward-producing structures and resources in Oncidiinae. The diversity of floral rewards affects the range of pollinators, which are related to the diversification of this subtribe throughout the Neotropics. The understanding of relationships between Oncidiinae species and their pollinators is crucial to our knowledge of the evolution of pollination systems in this huge plant family represented by the orchids.

Presence of the anther gland is a key feature in pollination of the early-branching papilionoids Dipteryx alata and Pterodon pubescens (Leguminosae)

The presence of glandular appendages in the anthers is a rare condition in angiosperms. In Leguminosae it occurs in species of the Mimosoid clade and in early-branching clades of papilionoids such as Dipterygeae. In Dipterygeae such appendages surprisingly exhibit a secretory cavity instead of secretory emergences as is the case for the Mimosoid clade. Thus, the objective of this study was to elucidate the function of anther glands in Dipteryx alata and Pterodon pubescens, species in the Dipterygeae clade that exhibit a pollen release mechanism that is intermediate between the explosive and valvular types. Flower buds and flowers were processed for surface, anatomical, histochemical and ultrastructural analyses. Anther glands consist of a cavity secreting sticky substances (oleoresins and polysaccharides) that play a key role during the flower's lifespan by aggregating pollen grains and attaching them to the floral visitor's body. Other floral features that are important for understanding the pollen release mechanism that is intermediate between the valvular and the explosive types are: (i) keel petals intertwined with tector trichomes; (ii) glandular appendages in the abaxial and lateral sepals and in petals composed of secretory ducts; and (iii) a continuous secretion process of the anther glands followed by an asynchronous dehiscence of anthers. The well-adapted papilionoid flag blossom with anther glands and keel petals intertwined with trichomes provided the foundation for a successful canalisation toward a pollen release mechanism intermediate between the explosive and valvular types inside early-branching papilionoids.

Pollinator-independent orchid attracts biotic pollinators due the production of lipoidal substances

Flowering plants often depend on the attraction of biotic pollinators for sexual reproduction. Consequently, the emergence and maintenance of selected floral attributes related to pollinator attraction and rewarding are driven by pollinator pressure. In this paper we explore the effect of pollinators, rainfall, temperature and air humidity on the reproduction of a Brazilian terrestrial orchid, Cranichis candida based on data of phenology, flower resources, olfactory and visual attraction cues, pollinators and breeding system. The flowers of C. candida are strongly protandrous and pollinated by workers of the social native bee Tetragonisca angustula. The bees collect labellar lipoidal substances (wax scales), which are transported to the nest. The lipoidal substance is composed of sterols, hydrocarbons and terpenes. The last presumably protects the bees and their nests against pathogens and other arthropods. C. candida sets fruits through biotic self- and cross-pollination, and spontaneously due the action of raindrops on flowers. Our results indicate that in C. candida, although rain-mediated spontaneous self-pollination happens, fructification mediated by biotic pollinations also occurs, which may result in fruit set by cross-pollination. A mixed pollination system must result in higher genetic variability when compared to species whose fruits are produced entirely by self-pollination. On the other hand, autogamy is a form of reproductive assurance, and has commonly evolved where pollination services are rare or absent.

Nectar-Secreting and Nectarless Epidendrum: Structure of the Inner Floral Spur

Epidendrum, the largest genus of Neotropical orchids, contains both nectar-secreting and nectarless species. Here, we compare the fine structure of the inner floral spur, termed the cuniculus, in nectariferous (E. difforme, E. nocturnum,E. porpax, E. rigidum, E. vesicatum) and seemingly nectarless (E. capricornu, E. ciliare, E. criniferum, E. pseudepidendrum, E. radicans, E. xanthoianthinum) species. This is the first time for such a detailed investigation of cuniculus structure to be undertaken for Epidendrum. Our aim was to characterize features indicative of secretory activity and to ascertain whether flowers presumed to be nectarless produce alternative pollinator food-rewards. The cuniculus is formed by fusion of the basal part of the labellum and column and extends alongside the ovary and transmitting tract. Our study indicates that all investigated species produce nectar or nectar-like secretion to varying degrees, and no alternative pollinator food-rewards were observed. Even though macroscopic investigation of presumed rewardless species failed to reveal the presence of secretion within the cuniculus, close observations of the cells lining the cuniculus by LM, SEM, and TEM revealed the presence of cuticular blisters and surface material. Moreover, the similarity of both the thick tangential cell walls (with the exception of E. vesicatum) and organelle complement of cuniculus epidermal cells in both copiously nectariferous species and those producing only small quantities of surface secretion confirmed the presence of secretory activity in species generally regarded to be rewardless. The secretory character was particularly obvious in the cells of the cuniculus of E. nocturnum, but also in E. ciliare, E. radicans and E. xanthoianthinum, since electron-dense cytoplasm and mitochondria, ER and secretory vesicles were abundant. Furthermore, cell wall protuberances occurred in E. nocturnum, which was indicative of intense transmembrane transport. This investigation highlights the need to examine more closely whether Epidendrum spp. considered to lack food-rewards based solely on macroscopic examination really are rewardless and deceptive.

Comparative reproductive biology and pollinator specificity among sympatric Gomesa (Orchidaceae: Oncidiinae)

The incredible pollination mechanisms displayed by orchid flowers has inspired biologists over the centuries. Based on the intriguing flower structures, the relationship among orchid species and their pollinators has been frequently regarded as very specialised. Given that visits on flowers pollinated by oil-collecting bees are regularly rare, and in Oncidiinae the flowers frequently attractexclusively species that act as effective pollinators, the comparative reproductive biology and pollinator specificity of two sympatric Gomesa (G. varicosa and G. montana; Oncidiinae) were analysedbased on records of floral morphology, production of floral rewards, pollinators and pollination mechanisms. Furthermore, experimental pollinations were carried out in order to examine the breeding systems. The results have show that in the studied population, both Gomesa are visited by several bee species, but these orchids present a specific pollination system.Pollinaria are deposited on the head of Centridini (G. varicosa and G. montana) and Epicharitini (G. varicosa) bees when landed on the central callus of the labellumto collect lipoidal substances produced by glandular elaiophores on lateral lobes of the labellum. Both species are dependent on a biotic pollen vector to set fruits. Gomesamontana is completely self-incompatible, while G. varicosa is partially self-compatible. Our results indicate that although the occurrence of self-sterile species seems to be common in Oncidiinae, in partially self-incompatible species, as is the case of G. varicosa, self-compatibility has been considered as an important factor favouring reproductive assurance in populations with low visitation frequencies, despite occurrence of inbreeding depression.

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.

Osmophore diversity in the Catasetum cristatum Lindl. alliance (Orchidaceae: Catasetinae)

Catasetum is a neotropical orchid genus of 130 species characterized by its unisexual flowers. They are pollinated by male Euglossini bees. It is widely know that these bees collect volatile compounds in Catasetum from structures called osmophores. However, there is little information on morpho-anatomy and histochemistry of secretory tissues for this neotropical genus and data are lacking. Based on these arguments members of the Catasetum cristatum alliance, namely C. arietinum, C. ariquemense, C. barbatum, C. carolinianum, C. cristatum, C. lanciferum, C. multifidum, C. multifissum, C. rivularium and C. semicirculatum were analyzed. The labellum of male flowers of this alliance is elongate and with fimbriate margins, possessing two protuberances and a median saccate portion. The labellum of female flowers is galeiform and there is no ornamentation. The entire adaxial surface of the labellum is secretory in both sexes, including the fimbriae of male flowers. The structure of the secretory tissue is similar among species, and they are composed of a simple epidermis and five layers of underlying parenchyma. In most species the epidermis is flat, and cells are elongated in the saccate portion. In C. ariquemense and C. carolinianum the epidermal cells are papilous, while in C. semicirculatum they have convex surface (male flowers). The histochemical analysis detected lipophilic droplets and starch grains inside the secretory cells. All characteristics observed are encountered in secretory tissues with high-energy demand, as is common in osmophores. 

Recent advances on evolution of pollination systems and reproductive biology of Vanilloideae (Orchidaceae)

Vanilloideae as currently circumscribed comprises nine genera and two tribes: Vanilleae and Pogonieae. The pantropical genus Vanilla has been frequently assumed to be natural on the basis of its climbing habit and lateral inflorescences. However, the inclusion of the rare Dictyophyllaria dietschiana in phylogenetic analyses makes the genus Vanilla paraphyletic. Within Pogonieae, phylogenetic analyses show that inclusion of Pogoniopsis turns the tribe paraphyletic. All analyses reveal that Pogoniopsis is closely related to members of Epidendroideae. Members of Pogonieae are pollinated by several groups of solitary and social bees, two pollination systems being recognized: reward-producing and deceptive. Molecular phylogeny suggests that the common ancestor to Pogonieae gave rise to two evolutionary lineages: one tropical with a condition of reward production; and one predominantly temperate-invading line with deceptive flowers. Reward-producing flowers characterize South and Central American clade (= Cleistes), while deceptive pollination is prominent in the clade including North American-Asiatic taxa plus Amazonian Duckeella. Species of “orchid bees” have been recorded as pollinators of the genus Vanilla (V. planifolia group and V. pompona group) in the Neotropics. In species of the V. pompona group, these bees are attracted by the fragrance of the flowers. Hummingbirds have been reported to pollinate some species of Vanilla. Vanilla insignis, V. odorata and V. planifolia are known to be pollinated through generalized food deception. Some species of Vanilla yield fruits through spontaneous self-pollination. This form of autogamy has been reported for V. griffithii, V. palmarum, V. planifolia, V. savannarum and V. bicolor. In Brazil, data on the pollination biology of Vanilla are scarce, but conclusive data are available for V. edwallii, which is pollinated by Epicharis (Apidae: Centridini). This species is rewardless, but male Epicharis are attracted to its flowers by their fragrance. Additionally, the Brazilian V. dubia and E. sclerophyllum are pollinated by bees. The mentum region of V. dubia and V. edwallii is dry, whereas that of E. sclerophyllum presents a small quantity of nectar. Flowers of E. sclerophyllum are scentless, while those of V. dubia are odoriferous. Vanilla dubia and V. edwallii are self-compatible and need a pollinator to yield fruits. In contrast, Epistephium sclerophyllum sets fruits through spontaneous self-pollination, but biotic pollination also occurs. Both species are primarily adapted to pollination by euglossine bees. Pollination by Euglossini seems to have evolved at least twice along the evolution of Vanilleae. Furthermore, shifts between rewarding and rewardless flowers and between autogamous and allogamous species have been reported among vanillas. 

Butterfly pollination in Pteroglossa (Orchidaceae, Orchidoideae): a comparative study on the reproductive biology of two species of a Neotropical genus of Spiranthinae

Spiranthinae orchids are known for being self-compatible and offering nectar as a reward. Although data on their pollinators are scarce, members of this tribe are mostly pollinated by bees, hummingbirds and moths. Some of them even reproduce through facultative self-pollination. Nothing is known about the pollinators and reproduction system in Pteroglossa. Based on records on flowering phenology, floral morphology, reward production, pollinators and breeding system, this paper aims to study the reproductive biology of two Pteroglossa spp. Both species offer nectar as a resource and are pollinated exclusively by diurnal Lepidoptera at the studied areas. Nectar is produced by two glandular nectaries, and is stored in a spur. Pollinaria possess a ventrally adhesive viscidium that is deposited on the basal portion of butterfly proboscides. Both species are self-compatible but pollinator-dependent. The reproductive success is low when compared to other Spiranthinae. Although no evident mechanical barrier to avoid self-pollination or geitonogamy was identified, the erratic behavior of the butterflies, with their infrequent visits to only one flower per inflorescence, contributes to an increased fruit set produced through cross-pollination. The presence of ventrally adhesive viscidia in Spiranthinae is responsible for greater pollinator diversity when compared to bee-pollinated Goodyerinae with dorsally adhesive viscidia, adapted to attach to bee mouthparts.

Floral biology of two Vanilloideae (Orchidaceae) primarily adapted to pollination by euglossine bees

Vanilloideae comprises 15 genera distributed worldwide, among which are Vanilla and Epistephium (tribe Vanilleae). Based on field and laboratory investigations, the pollination biology of V. dubia and E. sclerophyllum was analysed. The former was surveyed in a semi-deciduous mesophytic forest at the biological reserve of Serra do Japi and in a marshy forest at the city of Pradópolis, southeastern Brazil. The latter was examined in rocky outcrop vegetation in the Chapada Diamantina, northeastern Brazil. In the studied populations, the tubular flowers of V. dubia and E. sclerophyllum were pollinated by bees. Pollen was deposited on either their scutellum (V. dubia) or scutum (E. sclerophyllum). The mentum region of V. dubia is dry, whereas that of E. sclerophyllum presents a small quantity of dilute nectar. Flowers of E. sclerophyllum are scentless, while those of V. dubia are odoriferous. Although V. dubia is self-compatible, it needs a pollinator to produce fruit. In contrast, E. sclerophyllum sets fruit through spontaneous self-pollination, but biotic pollination also occurs. Both species are primarily adapted to pollination by euglossine bees. Pollination by Euglossina seems to have occurred at least twice during the evolution of Vanilleae. Furthermore, shifts between rewarding and reward-free flowers and between autogamous and allogamous species have been reported among vanillas.

Reproductive biology of Trichocentrum pumilum: an orchid pollinated by oil-collecting bees

The reproductive biology, reward production and pollination mechanism of Trichocentrum pumilum were studied in a gallery forest in the interior of the State of São Paulo, southeast Brazil. The floral visitors and pollination mechanism were recorded, and experimental pollinations were carried out in order to determine the breeding system of this species. Trichocentrum pumilum blooms in spring. Each paniculate inflorescence bears an average of 85 flowers that present a central yellow callus and finger-like trichomes on the lateral lobes of the lip. A lipoidal substance is produced and stored among these trichomes. In the studied population, T. pumilum is exclusively visited and pollinated by two bee species (Tetrapedia diversipes and Lophopedia nigrispinis). Pollinaria are deposited on mouthparts of bees during collection of the lipoidal substance from the lateral lobes of the labellum. Trichocentrum pumilum is self-incompatible and pollinator-limited. Natural fruit set was low (9%, compared to 45% in experimentally cross-pollinated flowers). Potentially viable seed exceed 97% in fruits obtained through cross-pollination and in natural conditions (open pollination).

Reproductive biology of Echinodorus grandiflorus (Alismataceae): evidence of self-sterility in populations of the state of São Paulo

Abstract The reproductive biology and the pollination of Echinodorus grandiflorus (Cham. & Schltdl.) Micheli were studied in populations native to interior of the State of São Paulo, Brazil. This species blossoms in summer and its flowers offer both nectar and pollen as rewards to pollinators. Nectar is produced in nectaries located at the base of the marginal carpels, opposite the petals. However, the effective pollinators (social and solitary bees), were recorded collecting pollen only. Visits, which can last from one or a few seconds to more than one minute, occur during the whole flower lifespan. Each flower opens at about 5:30 a.m. and lasts circa eight hours. All plants in the studied populations produce only hermaphrodite flowers. Percentage of pollen viability is 75%. The studied populations are self-incompatible and, as a consequence, pollinators are needed to transfer pollen among individuals. In natural conditions and after hand cross-pollinations, all receptacles presented mature achenes. Based on the analyses of pollen tube growth from hand self-pollinated flowers, and as a consequence of achenes abortion circa 30 days after self-pollinations, the populations of E. grandiflorus studied apparently presents a mechanism of late-acting self-sterility.

Reproductive biology of Cyrtopodium polyphyllum (Orchidaceae): a Cyrtopodiinae pollinated by deceit

The genus Cyrtopodium comprises about 42 species distributed from southern Florida to northern Argentina. Cyrtopodium polyphyllum occurs on rocks or in sandy soils, in restinga vegetation along the Brazilian coast. It flowers during the wet season and its inflorescences produce a high number of resupinate yellow flowers. Cyrtopodium polyphyllum offers no rewards to its pollinators, but mimics the yellow, reward-producing flowers of nearby growing Stigmaphyllon arenicola (oil) and Crotalaria vitellina (nectar) individuals. Several species of bee visit flowers of C. polyphyllum, but only two species of Centris (Centris tarsata and Centris labrosa) act as pollinators. Visits to flowers of C. polyphyllum were scarce and, as a consequence, low-fruit set was recorded under natural conditions. Such low-fruit production contrasts with the number of fruits each plant bears after manual pollination, suggesting deficient pollen transfer among plants. C. polyphyllum is self-compatible and has a high-fruit set in both manual self- and cross-pollinated flowers. Furthermore, fruits (2%) are formed by self-pollination assisted by rain. This facultative self-pollination mechanism is an important strategy to provide reproductive assurance to C. polyphyllum as rainfall restricts the foraging activity of its pollinating bees. Fruits derived from treatments and under natural conditions had a similar high rate of potentially viable seed. Moreover, these seeds had a low polyembryony rate, which did not exceed 5%. C. polyphyllum acts by deceit involving optical signals and exploits other yellow-flowered species within its habitat by attracting their pollinators. The low capsule production under natural conditions was expected, but its reproductive success is assured through self-pollination by rain and high seed viability.

Reproductive biology and pollination mechanisms of Epidendrum secundum (Orchidaceae). Floral variation: a consequence of natural hybridization?

The phenology, flower morphology, pollination mechanism and reproductive biology of Epidendrum secundum were studied in a semi-deciduous forest at the Serra do Japi (SJ), and in the Atlantic rain forest of Picinguaba, both natural reserves in the State of São Paulo, southeastern Brazil. E. secundum flowers all year round, with a flowering peak between September and January. This species is either a lithophytic or terrestrial herb in the SJ, whereas, in Picinguaba, it grows mainly in disturbed areas along roadsides. E. secundum is pollinated by several species of diurnal Lepidoptera at both study sites. In Picinguaba, where E. secundum is sympatric with E. fulgens and both share the same pollinators, pollen transference between these two species was recorded. E. secundum is self-compatible but pollinator-dependent. It is inter-compatible with E. fulgens, producing fertile seeds. In contrast to the population of the SJ, in the Picinguaba region, floral morphology is quite variable among plants and some individuals present flowers with characteristics in-between both sympatric species, suggesting that natural hybridization occasionally occurs. The anthropogenic perturbation is probably the cause of the occurrence of E. secundum in the Picinguaba region, enabling its contact with E. fulgens.

At daybreak--reproductive biology and isolating mechanisms of Cirrhaea dependens (Orchidaceae)

Floral biology, reproduction, pollinator specificity, and fruit set of Cirrhaea dependens were recorded in forest areas of Southeastern Brazil. Cirrhaea dependens is a lithophytic or epiphytic herb occurring very sparsely below dense canopies. Nearly all the flowers of a single plant open simultaneously before dawn. They are short-lasting and offer floral fragrances as rewards, which are collected by male euglossine bees. Observations carried out in mesophytic forests at Serra do Japi revealed that Euglossa VIRIDIS is their principal pollinator, with Eufriesea violacea a sporadic co-pollinator. Visitation started soon after flower opening, and attractiveness remained high for about 2 h, decreasing abruptly at sunrise. Flower anthesis with subsequent fragrance release seems to be correlated with bee attraction. Observations using chemical baits were carried out at Serra do Japi, and in the Atlantic Rain Forest of Picinguaba. Three euglossine species were captured with pollinaria of C. dependens in Picinguaba, whereas only E. violacea was attracted in Serra do Japi. In Picinguaba, C. dependens occurs sympatrically with C. saccata and C. loddigesii. Each species attracted different pollinators. The specificity and resulting reproductive isolation are due to the production of different odours by each orchid species. Cirrhaea dependens is self-compatible but pollinator-dependent. The reproductive success was low and appears to result from a combination of factors discussed here, such as the production of short-lived flowers, presence of floral mechanisms avoiding self-pollination, non-synchronization of flower phases among plants, and populations with few and sparsely distributed individuals.