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Brazilian Journal of Botany

Print version ISSN 0100-8404On-line version ISSN 1806-9959

Rev. bras. Bot. vol.31 no.3 São Paulo July/Sept. 2008

http://dx.doi.org/10.1590/S0100-84042008000300015 

ARTICLES

 

Pollination biology in Jacaranda copaia (Aubl.) D. Don. (Bignoniaceae) at the "Floresta Nacional do Tapajós", Central Amazon, Brazil1

 

Biologia da polinização de Jacaranda copaia (Aubl.) D. Don (Bignoniaceae) na Floresta Nacional do Tapajós, Amazônia Ocidental, Brasil

 

 

Márcia Motta MauésI, 2; Paulo Eugênio A. M. de OliveiraII; Milton KanashiroI

IEmbrapa Amazônia Oriental, Laboratório de Entomologia, Caixa Postal 48, 66017-970 Belém, PA, Brazil
IIUniversidade Federal de Uberlândia, Departamento de Biociências, Caixa Postal 593, 38400-902 Uberlândia, MG, Brazil

 

 


ABSTRACT

Jacaranda copaia (Aubl.) D. Don is a pioneer tree widespread in the Brazilian Amazon, usually found colonizing forest gaps and altered areas, and the forest fragment edges. This study investigated aspects of the floral biology, breeding system and pollinators of J. copaia trees. Flowering lasts from August to November, during the low rainfall period extending up to four weeks per tree and 3-4 months for the population as a whole, characterizing a cornucopia flowering pattern. The fruit set ends in the beginning of the rainy season, with wind dispersed winged seeds. Fruit set from open pollination was 1.06% (n = 6,932). Hand pollination using self-pollen (n = 2,099) did not set fruits. Cross-pollination resulted in 6.54% fruit set (n = 2,524), representing six times more than the natural pollination rate (1.06%, n = 6,932). Flowers excluded from insect visitation (automatic self-pollination) did not set fruits (n = 5,372). Pollen tube growth down to ovary was detected under fluorescence microcoscopy in cross-pollinated and selfed pistils. The species is an obligate allogamous plant, with late-acting self-incompatibility system. Approximately 40 species of native bees visited the flowers, but the main pollinators were medium-sized solitary bees as Euglossa and Centris species due to the compatibility between their body sizes with the corolla tube, direct contact with the reproductive structures and high frequency of visits.

Key words: bees, floral biology, late-acting self-incompatibility (LSI), phenology, pollinators


RESUMO

Jacaranda copaia (Aubl.) D. Don é uma árvore pioneira distribuída por toda Amazônia brasileira, encontrada colonizando clareiras, áreas alteradas e bordas de fragmentos florestais. O presente estudo investigou aspectos da biologia floral, sistema reprodutivo e polinizadores de J. copaia. O florescimento ocorre de agosto a novembro, durante o período de menor precipitação pluviométrica, estendendo-se por até quatro semanas por indivíduo e três ou quatro meses para a população, caracterizando um padrão de floração cornucopia. A frutificação termina no início da estação chuvosa, com a dispersão anemocórica das sementes aladas. A taxa de frutificação natural foi de 1,06% (n = 6.932). As flores autopolinizadas manualmente (n = 2.099) não produziram frutos. A polinização cruzada (n = 2.524) resultou em 6,54% frutos, representando seis vezes mais do que a polinização natural (1,06%, n = 6.932). As flores protegidas da visita de polinizadores (autopolinização espontânea) não formaram frutos (n = 5.372). O crescimento dos tubos polínicos foi detectado sob microscopia de fluorescência tanto nos pistilos autopolinizados quanto nos submetidos à polinização cruzada. A espécie foi considerada alógama obrigatória, com mecanismo de auto-incompatibilidade de ação tardia. Aproximadamente 40 espécies de abelhas nativas visitaram as flores, entretanto os polinizadores legítimos foram principalmente abelhas solitárias de médio porte dos gêneros Euglossa e Centris, em função da compatibilidade entre o tamanho corporal com o tubo da corola, que facilitava o contato direto com as estruturas reprodutivas, e a elevada freqüência de visitas.

Palavras-chave: abelhas, auto-incompatibilidade de ação tardia, biologia floral, fenologia, polinizadores


 

 

Introduction

Large rainforest woody species are commonly self-incompatible (Bawa 1974, 1990) and dependent on long distance pollinators. But despite low density and sometimes asynchronous flowering, which have led to misconceptions about the ability of these plants to attract pollinators and have allogamous fruit set (Corner 1954, Fedorov 1966), they do attract efficient long distance pollinators as large solitary or subsocial bees (Bawa et al. 1985, Dick et al. 2004). For the tropical Bignoniaceae, a diverse assemblage of pollinators seems to have influenced flowering morphology and guaranteed fruit-set of these largely self-incompatible plants (Gentry 1974a, Gibbs & Bianchi 1999, Bittencourt Júnior & Semir 2004, Gottsberger & Silberbauer-Gottsberger 2006). Flowering phenology patterns, defined according to the duration and intensity, were also related with pollination biology (Gentry 1974b, Van Schaik et al. 1993, Morellato et al. 2000).

Despite numerous studies on pollination biology of the Bignoniaceae, few published studies have been focused so far on Jacaranda species, e.g. J. macrantha Cham. (Bittencourt 1981), J. caroba (Vell.) A. DC. (Vieira et al. 1992) and J. racemosa Cham. (Bittencourt Júnior & Semir 2006). These studies showed clear evidences of self-incompatibility (SI) (Bittencourt 1981) and ovarian or late-acting self-incompatibility (LSI) (Vieira et al. 1992, Bittencourt Júnior & Semir 2006). Gottsberger & Silberbauer-Gottsberger (2006) discuss about the superimposed pollination system of this genus, where three layered types of pollination coexist.

Jacaranda copaia (Aubl.) D. Don are medium to large trees, up to 30-35 m tall and 75 cm of DBH under natural conditions (Silva et al. 1985). It is a pioneer tree, usually found colonizing forest gaps, altered areas, and the edge of forest fragments (Guariguata et al. 1995). The species can also be established inside the forest, where adult trees can reach the canopy, despite being more frequent at the understory (Ribeiro et al. 1999). The species is distributed in the Neotropical region, widespread in lowland moist and wet forest from Belize to Bolivia, where two subspecies coexist (Gentry 1992), J. copaia subspecies copaia and J. copaia subspecies spectabilis, which are distinguished by features of the leaves and fruits. However, the acceptance of these subspecies is still controversial (Ribeiro et al. 1999, Lohmann et al. 2006, Lohmann & Ulloa-Ulloa 2006). J. copaia has been recommended for use in agroforestry, reforestation and degraded land recovery projects in South and Central America (Brienza Júnior et al. 1991), but basic information on its reproductive biology in order to subsidize its use was still lacking.

In this study, floral biology and breeding system of J. copaia were investigated in Pará State, Brazil, in order to provide information to future species use and management. The species is one of the target species of the Dendrogene project, coordinated by Embrapa Amazônia Oriental and several partners. In this project, some woody species with different ecological growing conditions and life history strategies are being studied for their genetic structure, reproductive process and regeneration (Kanashiro et al. 2002).

 

Material and methods

The main study area was located at the "Floresta Nacional doTapajós" (Flona Tapajós), in central Brazilian Amazon (2.89° S and 54.95° W). It comprises approximately 600,000 hectares of lowland native forest which has been submitted to controlled timber extraction and sustainable forest management studies (Silva et al. 1985, Kanashiro et al. 2002). The climate, according to Köppen classification, is AmW, characterized by annual dry period of 2-3 months and average rainfall of 2,000 mm (600 mm to 3,000 mm) (Espírito-Santo et al. 2005). The average annual air temperature is 25 °C, mean relative humidity is 86% (Carvalho et al. 2004). This forest may experience severe drought during El Niño events (Nepstad et al. 2002). From 1999 to 2004, a low impact selective logging project was conducted in 3,222 hectares under supervision of the "Instituto Brasileiro do Meio Ambiente e Recursos Naturais Renováveis" (Ibama) and the International Tropical Timber Organization (ITTO). The study plot was a 500 ha area within this larger area most of which is still untouched forest.

Complementary studies on floral biology and reproductive systems were also done with adult trees (> 20 years) planted at the experimental area of "Embrapa Amazônia Oriental" in Belém, Pará State (1°27' S and 48°29' W). The climate according to Köppen, is Afi, characterized by an average annual temperature of 25.9 °C (21 °C to 31.6 °C) and annual average rainfall of 2,900 mm.

Phenological observations were carried out every two weeks from October 2001 to July 2004 on 60 Jacaranda copaia trees, considering the occurrence, duration and frequency of the following events: (1) flowering (e.g., floral buds and flowers); (2) fruit set (e.g., immature fruit, mature fruit and seed dispersal) and (3) leaf changes (e.g., juvenile and mature leaf; partial and total defoliation), in accordance with the methodology of Fournier & Charpantier (1975). The phenological records were associated with meteorological data (e.g., precipitation, temperature, relative humidity and photoperiod) obtained in the same area from 2001 to 2003 by the LBA Project Team (2007), in accordance with Miller et al. (2004).

Inflorescence structure, flower morphology and aspects of the floral biology (anthesis, number of flowers opened/day, flower longevity, stigma receptivity, pollen viability, osmophores detection, sugar concentration and volume of the nectar, pollen/ovule ratio), were observed in five trees at Belém area, from August to October 2002. Peroxtesmo KO (Dafni & Maués 1998) was used to check stigma receptivity. The Peroxtesmo test indicates the main receptive area on the stigma surface, which turns dark blue or purple in contact with the solution. Pollen viability was tested with the DAB procedure (Sigma FastTM 3.3' diaminobenzidine) and in vitro pollen germination on sucrose and agar medium (Dafni et al. 2005). The osmophores were detected with neutral red solution (1:10,000; Kearns & Inouye 1993) in fresh flowers. The flowers were immersed in the neutral red solution for 30 minutes, removed and washed in distilled water. Nectar was removed from previously bagged flowers and volume estimated with 1 µL glass microcapillary tubes. This procedure was carried out on fresh flowers (n = 30) (two hours after fully opening) and other 30 flowers one day after opening. Total sugar concentration or "sucrose equivalents" on the nectar was scored after volume measurements with a Bellingham & Stanley pocket refractometer (Dafni et al. 2005). Different parts of the flower (corolla, calyx, staminode, stamens, pistil) where placed in covered glass vials for 5-10 minutes to organoleptic evaluation of scent (Dafni et al. 2005).

Fresh flowers were collected and fixed on FAA (acetic acid 5%, formaldehyde 5% and ethanol 90%) and 48 h later transferred to ethanol 70% for laboratory analysis. The floral morphology was described using stereomicroscope and scanning electron microscope (SEM). Flower structure, size, shape and color, as well as number of flowers per inflorescence, number of opened flowers per day and flower longevity were documented. Flower measurements were carried out for fixed flowers in five plants. The number of ovules and anthers were counted under stereomicroscope. The number of pollen grains was estimated in three flowers of each five plants, using all four anthers per flower, with a haematocytometer. To estimate the number of pollen grains per flower, each anther was gently squashed in 1 mL of 50% ethanol + 0.5%-1% of detergent, to facilitate pollen removal and homogeneous spread of pollen for counting under microscope. Six sub samples of 1 µL where dropped on the haemacytometer, counting all the pollen grains in a surface unit (Dafni et al. 2005).

Hand pollination experiments in previously bagged flowers were also performed to evaluate breeding system using five different trees. The subsequent treatments were carried out (following Radford et al. 1974): (1) cross-pollination; (2) manual self-pollination; (3) spontaneous (automatic) self-pollination; (4) control – tagged flowers left to natural pollination. Fruits set from each treatment were monitored until the complete fruit maturation, denoted by the beginning of capsules' dehiscence. In order to access the pollen germination and pollen tube growth by means of aniline blue staining and fluorescence microscopy (Martin 1959), 20 pistils of each treatment were collected 24 h and 48 h after manual pollination, fixed in FAA for 48 h and preserved in ethanol 70%. The index of self-incompatibility (ISI) was assessed by the ratio between fruit set from self- and cross-pollinated pistils (Bullock 1985). The reproductive efficacy (RE) was obtained by the ratio between fruit set of natural and cross-pollinated pistils (Ruiz & Arroyo 1978).

In order to have access to tree crown and observe flower visitors, a 34 m wood tower with a 2 m2 platform on its top was built beside a target tree at the Tapajós forest site. Similar platforms with 10-18 m were also built beside J. copaia trees at the Embrapa site, to facilitate the handling of the flowers throughout the controlled pollination experiments. Observations of insect behavior on the flowers were accomplished, as well as capture with insect nets and photographic records, in order to identify legitimate pollinators. Frequency of visits was considered as follows: high (more than 20 visits per day), medium (at least 10 visits per day) and low or occasional (less than five visits per day). The observations were performed from 7:00 a.m. (anthesis initiation) to 18:00 p.m. during five days (approximately 50 h). Most insects were identified by comparison with previously identified specimens in the Entomological collection of Embrapa Amazônia Oriental. The following data about the insect visitors were registered: (1) species name; (2) if there was any contact between the visitor body and the reproductive structures of the flowers; (3) if pollen or nectar was collected and/or consumed. These observations were carried out during the main flowering season of 2001-2002, from September to October, corresponding to approximately 82 h of observations. Voucher specimens of the studied plants, insect visitors and pollinators, were deposited at the IAN Herbarium (numbers 178633, 176899, 176900, 17901, 17902) and the Entomological Museum of the Embrapa Eastern Amazon.

 

Results

Jacaranda copaia displays large erect panicles up to 37 cm long at the branches' tip, with an average of 3,596 flowers (± 613, n = 9) per inflorescence and 96.4 ± 58 (n = 16) opened flowers per inflorescence per day during the peak of the flowering phase. The total blooming per inflorescence lasted an average of 35 days (± 11, n = 5).

The most expressive flowering period occurred during the dry season, extending from September to December, when up to 97% of the individuals were flowering (figure 1). The same pattern was found during the whole study period, characterizing an annual flowering pattern (sensu Newstrom et al. 1994). Fruit set occurred from November to March, and the seed dispersal was concentrated during the peak of the raining season, from February to May. Leaf changes occurred just prior to the flowering phase, mainly from June to August.

 

 

The flowers are hermaphrodite, zygomorphic and nectariferous. The calyx is short (5-6 mm), cupular, brown, glabrous and gamosepalous. The corolla is tubular-infundibuliform, violet-blue (or lilac) in the outer surface and white inside the petal hood (throat), pubescent, gamopetalous, with five free lobes, 2.4-3.0 cm long. Androecium presents four didynamous stamens and one visually attractive staminode with glandular trichomes and bifurcated apex. Anthers are basifixed and monothecate (divaricate) with a mostly apical longitudinal opening, which remains partially closed after the dehiscence, without exposing totally the pollen grains (figure 2C and 5). The gynoecium presents a single filiform style, shorter than the staminode, with a bilobed tactile and humid stigma covered with clavate papillae of distinct lengths at the inner surface (figure 2A, 2E, 4, 5 and 6), and a flattened and elongated ovary containing an average of 243 (± 33, n = 20) ovules.

 

 

 

 

 


 

During pre-anthesis phase flower buds were closed only by the petals edges, which opens with the simple touch of the first visitor. The anthesis started from 7:30 to 8:30 a.m, according to visitors' movement. The nectary is a disk located at the base of the ovary. The anthers dehisced soon after full anthesis phase, but the pollen was released only when the visitors squeezed the anthers, removing small amounts of pollen grains. The number of pollen grains estimated per flower was 30,425 (n = 4), and the pollen/ovule ratio was 125.2. The osmophores were mainly located in the corolla and staminode, which was consistent with results of the organoleptic test.

The best sucrose concentration for pollen germination was 25%, in which case 70.8% of the pollen spread on the agar media after 24 hours exhibited pollen tube growth. The DAB test showed highest pollen viability period among 8:00 to 9:00 a.m. (75.5%), decreasing gradually during the rest of the day (figure 3). The nectar was produced in small amounts during the flower life span. The average volume in first day flowers was 1.01 µL (± 0.2, n = 20; 0.5 to 1.5 µL) and for second day pistils the volume was 1.06 µL (± 0.3, n = 32; 0.5 to 2 µL). Sugar concentration varied from 23% to 41% (mean = 28.5% ± 4.4; n = 19) for first day flowers and from 20% to 53 % (mean = 34.7% ± 6.7; n = 31) for second day remaining pistils. Stigma receptivity is mainly located at the inner surface (papillate) region, lasting from the anthesis until 24 h of lifespan, as shown by the Peroxtesmo KO tests.

Flowers had a life span of approximately 24 h (intact flower – holding all the verticiles), after which the corolla collapsed together with the stamens and staminode. The calyx, nectary disc and pistil lasted for another day, and nectar was still secreted, although very few visitors collected nectar during this second day. Total abscission of these flower structures occurred 48 h after flower opening. The dry dehiscent fruits took approximately four months to mature and comprised an average of 245 winged seeds (± 26, n = 25), which were wind dispersed.

There was a plethora of 61 different species of flower visitors, including medium to large-sized bees, butterflies, wasps and hummingbirds (table 1). Medium-sized bees belonging to the genus Euglossa and Centris, were the most frequent visitors in both study sites and the main pollinators due to their frequency, body size and behavior. These bees were usually the first visitors, assisting in the process of anthesis, as they touched the petal lobes triggering their final expansion and corolla opening. The visits of Centris were very fast, lasting from 3 to 6 s (n = 46). The euglossine bees were very frequent visitors and their visits lasted 8 to 12 s (n = 55). The Centris spp. entered the flower tube and collected both nectar and pollen, pollen collection indicated by body grooming after visits. As for Centris spp., Euglossa bees contacted reproductive structures at every visit while entering the corolla tube. When leaving the corolla chamber they squeezed the anthers, receiving pollen on the upper head and thorax. Their long glossa proved to be very useful in nectar collection. Euglossa males were also frequent visitors, but they were more restricted to the upper part of the corolla chamber, where they grasped the inner petal surface and, apparently the staminode trichomes glands. Halictidae (Augochlora, Augochloropsis, Pseudoaugochloropsis), Exomalopsis and Meliponina (Paratetrapedia) used the staminode as a bridge to access the nectary, and sometimes collected pollen adhered to its trichomes, behaving as occasional pollinators.

 

 

The flower visitation period extended from 7:30 a.m. to 17:00 p.m., with higher frequency of bees from 8:00 to 10:30 a.m. Xylocopa frontalis visited the flowers at irregular intervals from the beginning of anthesis to the end of the day, perforating the base of the corolla tube to take the nectar in illegitimate visits which resulted in no pollination. Butterflies were late visitors, from 11:00 a.m. to 15:30 p.m., and nectar robbers, using the holes made by X. frontalis to access the nectar chamber. The legitimate and illegitimate pollinators visited the flowers together along the day, although the illegitimate visitors (e.g. Xylocopa and butterflies) were more frequent during the afternoon. No aggressive behavior was noticed among them.

Controlled pollination tests (table 2) resulted in no fruit set from manual and automaticself-pollination, although a single selfed fruit was initiated and aborted two weeks after manual pollination. Fruit set from open pollination was initially 4.99% but only 1.06% reached maturation (n = 6,932). Cross-pollination resulted in 21.7% of initiated fruits but only 6.54% reached maturation (n = 2,524). Pollen tube growth was detected both in self and cross-pollinated pistils after the first 24 hours, but only cross-pollen penetrated the ovules (figure 7).

 

 

Discussion

Jacaranda copaia flowers attributes, such as diurnal anthesis, tubular violet zygomorphic corolla, presence of nectar in a protected chamber, hidden reproductive organs and sweet fragrance are compatible with the bee pollination syndrome (Faegri & van der Pijl 1979, Proctor et al. 1996). According to Gentry's (1974a) classification, Jacaranda copaia flowers belong to the Anemopaegma type, generally pollinated by medium to large bees, usually Euglossini and Anthophorinae, although it may be visited by illegitimate pollinators, nectar and pollen robbers (e.g. Trochlidae, Meliponina, Lepidoptera and Xylocopa). The anther's monothecate type is atypical within the genus Jacaranda, as most species presents dithecate anthers (Dr. Lúcia Lohmann, unpublished data).

The flowering phenology of Jacaranda copaia can be classified as cornucopia (Gentry 1974b) with a relatively long and massive flowering period between 3 to 10 weeks. The large and showy inflorescences at the canopy layer, with hundreds of flowers opening at the flowering peak, results in a flowering display which may attract visitors from long distances. This flowering pattern seems to be the most widespread and generalized among the Bignoniaceae (Gentry 1974a)

The corolla tube allowed visits of small to medium-sized bees and was a constraint to larger visitors. The position of the anthers and stigma inside the petal hood promoted the pollen deposition on the upper head and thorax of the pollinators. The basal constriction of the corolla tube was compatible with long-tongued bees, such as Euglossa, as reported also by Bittencourt Júnior & Semir (2006). The same foraging behavior of these agents was registered in the pollination biology of Arrabidaea conjugata (Vell.) Mart. (Correia et al. 2005) and Jacaranda racemosa Cham. (Bittencourt Júnior & Semir 2006).

Euglossini female bees were considered the most efficient melittophilous pollinators of Bignoniaceae species in Panama (Gentry 1974b). The characteristic long glossa of this tribe helps in the process of nectar foraging in tubular flowers (Pinheiro & Schlindwein 1998). Centris were also reported as main pollinators of Tabebuia flowers in Costa Rica (Frankie et al. 1983) and Central Brazil (Barros 2001). Besides, Centris spp. bees also demonstrated compatible pollinator behavior, once they penetrated up to the second third of the corolla tube (distal part), where the anthers and stigma are located, and thus were able to properly transfer pollen to the reproductive structures.

On the other hand, some of the visitors, as Xylocopa frontalis, which were not able to enter the corolla tube, collected nectar by perforating the soft corolla tissue at the nectary level. This behavior has been recognized in many species of the Bignoniaceae family (Gentry 1974a, b, Gobatto-Rodrigues & Stort 1992, Vieira et al. 1992, Galetto 1995, Correia et al. 2005) and is repeated by Xylocopa bees in other plants with tubular flowers (Barrows 1980).

The staminode "selected" the legitimate visits reducing the corolla chamber, therefore large-sized visitors were not able to properly enter the flower and contact the stigma and anthers, although some species such as Centris flavifrons, C. similes, Eulaema meriana, Epicharis rustica, Bombus, Eufriesea and Oxaea forced the entrance and acted as occasional pollinators, usually collecting nectar. It was also used as a platform by smaller bees such as Meliponina, Halictidae and Exomalopsis, which used the staminode as a path to reach the nectar chamber.

The staminode function has been comprehensively discussed (Bittencourt Júnior & Semir 2006, Gottsberger & Silberbauer-Gottsberger 2006). Vieira et al. (1992) suggested that this structure had three different functions in Jacaranda caroba (Vell.) DC. flowers: visual orientation, smell attraction guide and assistance in the contact of the pollinators with the reproductive structures. It has been also suggested that the staminode may be used as a bridge by halictid bees to reach the anthers, eventually touching the stigma (Gottsberger & Silberbauer-Gottsberger 2006). It also retains pollen grains on the glandular hairs (trichomes), which are collected by bees (Morawetz 1982 apud Gottsberger & Silberbauer-Gottsberger 2006), and diminishes the space inside the corolla chamber, thus promoting better contact of the pollinators with the reproductive organs (Bittencourt Júnior & Semir 2006). In J. copaia, all those functions can be assumed.

Finally, staminode's trichomes secret a scent (Bittencourt Júnior & Semir 2006) which may explain the visits of Euglossa males. Due to those different attractants, including nectar, pollen and scent, besides the multiple role of the staminode adapting the flower to different sizes of visitors, Jacaranda seems to have superimposed pollination systems (Gottsberger & Silberbauer-Gottsberger 2006).

Jacaranda copaia is self-incompatible with abscission of selfed pistils within one or two days after hand pollinations. ISI was null and the reproductive efficacy 0.16 was very low, indicating that natural pollination in the Belém plantation is much less efficient than hand cross pollination. Pollen germination and pollen tube growth was similar in both self and cross-pollinated pistils, but in selfed pistils the pollen tubes were not observed penetrating the ovules. This type of late-acting self-incompatibility system (LSI) or ovarian self-incompatibility (Seavey & Bawa 1986) is common in many tropical Bignoniaceae, including Tabebuia aurea (Manso) Benth. & Hook. f. ex S. Moore (syn. T. caraiba) and T. ochracea (Cham.) Standl. (Gibbs & Bianchi 1993, Barros 2001), Dolichandra cynanchoides Cham. and Tabebuia nodosa (Griseb.) Griseb. (Gibbs & Bianchi, 1999), Jacaranda macrantha (Bittencourt 1981) and Jacaranda racemosa (Bittencourt Júnior & Semir 2006). Studies over the last two decades have shown that outbreeding and LSI are common features in many tropical trees (Bawa et al., 1985) but seem to be such common features in the Bignoniaceae that a phylogenetic component has been argued to explain such familial clustering (Gibbs & Bianchi 1999). However, self-fertility and apomixis have been also described in some woody tropical Bignoniaceae (Costa et al. 2004). The extremely low fruit set from open pollination is consistent with other tropical trees (Bawa et al. 1985).

The pollen/ovule ration sensu Cruden (1977) indicated that the species would be self-compatible, but field tests on the reproductive system refuted that supposition. The pollen grains are not exposed, but released from the anthers in small amounts according to pollinators' movements in the flowers. This may result in a very efficient pollen dispensing and pollination strategy, which may explain the relatively low number of pollen grains produced per flower. In Arrabidaea conjugata the pollen was released by the same process, therefore even when visitors arrived at the end of the anthesis they still can be dusted with pollen grains (Correia et al. 2005).

The legitimate visitors observed confirmed the melittophilous pollination syndrome sensu Faegri & van der Pjil (1979) in J. copaia. Solitary bees tend to show higher oligolectic species-specific preferences (Cane 2001), but the superimposed pollination system (Gottsberger & Silberbauer-Gottsberger 2006), with nectar, pollen and perfume as rewards, would explain the great number of potential pollinators attracted. Hummingbird pollination is reported in Zeyheria montana. Mart. (Bittencourt Júnior & Semir 2004), but in J. copaia these agents were considered simply occasional pollinators, due to their low frequency and unspecialized bird syndrome flower traits. Cornucopia flowering phenology also contributes to long distance pollinators' attraction. Roubik & Degen (2004) modelling studies with J. copaia trees at the "Floresta Nacional do Tapajós", showed that this species was nearly completely out-crosser and the mean pollen dispersal range was 147.9 (± 42.0 m). Assuming that in this site the species is regularly distributed (1.8 trees > 20 cm DBH per hectare), and considering its diversified pollination system, we expect the maintenance of the reproductive success of J. copaia under natural conditions.

Acknowledgements - The authors are grateful to the Dendrogene team, to the Department for International Development (DFID) and Embrapa for their support during all the study phases. To the "Floresta Nacional do Tapajós" Administration (Ibama), for the permission to work at the study site. To Lyn Loveless (College of Wooster, Ohio, USA) and David Boshier (Oxford Forestry Institute, UK), for valuable discussions and guidance. We also thank Antônio Elielson Rocha from the Museu Paraense Emílio Goeldi, who prepared the flower illustration; Francisco G. da Silva Frota, Domingos de Jesus Araújo, Marco Antônio Cordeiro and Reginaldo Medeiros (Entomology lab, Embrapa Amazônia Oriental) along with Milene Souza, Fernando Santos and Gleicilene Almeida (Universidade Federal Rural da Amazônia) who assisted in field and lab work; Dr. David W. Roubik (Smithsonian Tropical Research Institute) and Dr. Fernando Silveira (Universidade Federal de Minas Gerais), who assisted with the bees' identification; two anonymous reviewers who helped to improve the manuscript and, last but not least, the field staff of the Dendrogene Project for all the effort during data collection and assistance inside the project area.

 

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(received: June 06, 2006; accepted: July 03, 2008)

 

 

1. Part of PhD thesis developed at the Universidade de Brasília, Departamento de Ecologia, Brasília, DF, Brazil.
2. Corresponding author: marcia@cpatu.embrapa.br

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