Nectar Removal Research Articles

Floral nectar production: what cost to a plant?

Floral nectar production is central to plant pollination, and hence to human wellbeing. As floral nectar is essentially a solution in water of various sugars, it is likely a valuable plant resource, especially in terms of energy, with plants experiencing costs/trade-offs associated with its production or absorption and adopting mechanisms to regulate nectar in flowers. Possible costs of nectar production may also influence the evolution of nectar volume, concentration and composition, of pollination syndromes involving floral nectar, and the production of some crops. There has been frequent agreement that costs of floral nectar production are significant, but relevant evidence is scant and difficult to interpret. Convincing direct evidence comes from experimental studies that relate either enhanced nectar sugar production (through repeated nectar removal) to reduced ability to produce seeds, or increased sugar availability (through absorption of additional artificial nectar) to increased seed production. Proportions of available photosynthate allocated by plants to nectar production may also indicate nectar cost. However, such studies are rare, some do not include treatments of all (or almost all) flowers per plant, and all lack quantitative cost-benefit comparisons for nectar production. Additional circumstantial evidence of nectar cost is difficult to interpret and largely equivocal. Future research should repeat direct experimental approaches that relate reduced or enhanced nectar sugar availability for a plant with consequent ability to produce seeds. To avoid confounding effects of inter-flower resource transfer, each plant should experience a single treatment, with treatment of all or almost all flowers per plant. Resource allocation by plants, pathways used for resource transfer, and the locations of resource sources and sinks should also be investigated. Future research should also consider extension of nectar cost into other areas of biology. For example, evolutionary models of nectar production are rare but should be possible if plant fitness gains and costs associated with nectar production are expressed in the same currency, such as energy. It should then be possible to understand observed nectar production for different plant species and pollination syndromes involving floral nectar. In addition, potential economic benefits should be possible to assess if relationships between nectar production and crop value are evaluated.

Comparative nectar dynamics in four ornithophilous Melocactus (Cactaceae) species in a seasonally dry tropical forest

AbstractNectar is an important floral resource, often representing the only source of water for pollinators in arid environments. We investigated whether successive nectar removal would affect the nectar production dynamics of four Melocactus species growing in the Caatinga domain. Nectar was serially extracted from flowers four times per day at regular 60‐min intervals after anthesis. The cactus species showed a consistent pattern of secretion linked to ornithophily, with no significant responses to successive nectar removal and no reabsorption. Nectar secretion covered the entire period of anthesis, starting at 2:30 p.m. and continuing to 5:30 p.m., with the production of 11–38 μl per flower, with sugar concentrations of 10%–32% (3–16 mg of sugar). Individual flowers produced average amounts of 16.9–3.43 mg of sugar per day, corresponding to energy values of 0.06–0.28 kJ. Sympatric populations produced an average of 150–200 flowers per day. The nectar produced by Melocactus can therefore meet the daily energy needs of hummingbirds, which is of special importance during the dry season, when resources are scarce in the Caatinga.

A negative association between nectar standing crop and pollen transfer suggests nectar functions as a manipulator of pollinating bats.

Nectar standing crop has a fundamental role in controlling pollinator movements between flowers and individuals within a population. In bat pollination systems, plants take advantage of the cognitive abilities of nectarivorous bats, which integrate complex perceptions of the quality and spatial distribution of resources. Here, we propose that associations between standing crop and pollen transfer help to reveal the role of nectar as a manipulator of pollinator behaviour. We used Harpochilus neesianus Ness (Acanthaceae), a bat-pollinated shrub from the Brazilian Caatinga, as a model system to assess nectar removal effects and standing crop, respectively, over the night and to test associations between the amount of nectar available to pollinators, and pollen import and export. Harpochilus neesianus showed continuous nectar secretion throughout the flower lifespan. Flowers subjected to successive nectar removals produced less nectar than flowers sampled just once, and showed, despite a higher sugar concentration, a lower absolute amount of sugar. Under these conditions, bats may realize that nectar production is decreasing after repeated visits to the same flower and could be manipulated to avoid such already pollinated flowers with little nectar, thus increasing the probability of visits to flowers with a high amount of nectar, and a still high pollen availability on anthers and low pollen deposition on stigmas. We found that during most of the period of anthesis, nectar standing crop volume was positively correlated with the number of pollen grains remaining in the anthers, and negatively with the number of pollen grains deposited on the stigma. Nectar secretion patterns can function as a manipulator of pollinating bats in H. neesianus. We propose that the assessment of variability in nectar secretion in response to removal, and the correlation between nectar standing crop and relative pollen transfer throughout anthesis should be considered in order to understand the role of nectar in the manipulation of pollinators.

Estimates of nectar productivity through a simulation approach differ from the nectar produced in 24 h

Abstract Nectar is a key resource for numerous insects. Despite its importance, nectar productivity has mainly been assessed using one sampling method, in which the volume of nectar produced by a flower is measured after 24 h of isolation from insects (‘measured 24 h volume’ hereafter). This method assumes that nectar removal by flower‐visiting insects does not affect nectar productivity. Hence, a linearity in the nectar production dynamic is assumed. The effect of nectar removal could lead to an actual volume of nectar produced per flower over 24 h being higher or lower than the measured 24 h volume. Whether the nectar productivity is influenced by insect activity still therefore needs to be assessed. In a field experiment, we estimated the nectar production dynamics of lavender (Lavandula hybrida) and fennel (Foeniculum vulgare) flowers and tested whether they met the linearity assumption. Then, we developed a simulation model to identify how different scenarios of insect foraging activity: nectar removal rate (average and maximum), and flower‐selection strategies (random selection or rewarding flower selection) alter the estimated 24 h volume of nectar for both crops (‘estimated 24 h volume’ hereafter). Finally, we tested whether the estimated 24 h volume differed from the measured 24 h volume for both crops. Lavender and fennel showed equal measured 24 h volume of nectar but the produced nectar volume over 6 h suggested that a flower of lavender was more productive than a flower of fennel. Both nectar production dynamics did not meet the assumption of linearity. The simulation models showed that the estimated 24 h volume increased with maximum nectar removal rate for lavender, and the opposite was found for fennel. Rewarding selection always increased the estimated 24 h volume for fennel while for lavender a positive effect was detected at average rate of nectar removal. We found that the estimated 24 h volume was always greater than the measured 24 h volume. Our model demonstrated that the effect of insect foraging activity on flower's nectar productivity should be considered while estimating the resources produced by plants. As an alternative, measures of produced nectar volume in short time spans may be compared with the measured 24 h volume to check the reliability of this widespread method. Read the free Plain Language Summary for this article on the Journal blog.

A Decrease in the Staminode-Mediated Visitor Screening Mechanism in Response to Nectar Robbers Positively Affects Reproduction in Delphinium caeruleum Jacq. ex Camb. (Ranunculaceae).

Simple SummaryNectar robbers frequently have direct or indirect negative effects on plant reproductive success. However, nectar robbers can also indirectly contribute to the reproductive success of plants in some cases. The negative effects of nectar robbing on plant reproductive success have been widely reported, but the reasons for possible positive effects demand further investigation. Hence, our study was designed to assess the effects of nectar robbers on the reproductive success of Delphinium caeruleum. This will facilitate an understanding of the mutualism between plants and their visitors.Nectar-robbing insects, which are frequently described as cheaters in plant–pollinator mutualisms, may affect plant reproductive fitness by obtaining nectar rewards without providing pollination services. The negative effects of nectar robbing on plant reproductive success have been widely reported, but the reasons for possible positive effects demand further investigation. The goal of the study was to evaluate the effects of nectar robbing on the reproductive success of Delphinium caeruleum. Two staminodes cover the stamens and pistils in the flowers of D. caeruleum, forming a “double door” type of structure that compels pollinators to physically manipulate the staminodes to access the sex organs. In order to explore whether the operative strength required to open the staminodes is affected by actions associated with nectar robbing, we set up five different treatment groups: no nectar robbing, natural nectar robbing, artificial nectar robbing, hole making, and nectar removal. A biological tension sensor was used to measure the operative strength required to open the staminodes in the flowers. We also assessed the effect of nectar robbing on the flower-visiting behavior of pollinators and the effect of nectar robbing on reproductive fitness by the flower. The results showed that the operative strength needed to open staminodes was reduced by nectar robbers but not by artificial nectar robbing, hole making, or nectar removal. The flowers’ continuous visitation rate and visitation frequency by pollinators decreased significantly in robbed flowers. Both the pollen export and pollen deposition in naturally robbed flowers were significantly higher than those in nonrobbed flowers. Our results demonstrate that nectar robbers play an indirect positive role in the reproductive fitness of D. caeruleum flowers by reducing the operative strength of staminodes to promote pollen transfer. The reduction in operative strength of staminodes might be an adaptive mechanism that responds to nectar robbing.

Corolla Abscission Triggered by Nectar Robbers Positively Affects Reproduction by Enhancing Self-Pollination in Symphytum officinale (Boraginaceae).

Nectar robbers, which affect plant fitness (directly or indirectly) in different degrees and in different ways, potentially constitute a significant part of mutualistic relationships. While the negative effects of nectar robbing on plant reproductive success have been widely reported, the positive effects remain unknown. The target of our study was to evaluate the effects of nectar robbers on the reproductive success of Symphytum officinale (Boraginaceae). We observed the behavior, species and times of visitors in the field, and we assessed the effect of nectar robbers on corolla abscission rate and time. To test the fitness of corolla abscission, we detected the changes in stigma receptivity, pollen viability, pollen amount and appendage opening size along with the time of flower blossom. The flowering dynamics and floral structure were observed to reveal the mechanism of self-pollination. Finally, pollen deposition seed set rate and fruit set rate were determined to estimate the effect of nectar robbers on reproduction success. We observed 14 species of visitors and 2539 visits in 50 h of observation; 91.7% of them were nectar robbers. The pressure and nectar removal of nectar robbers significantly promoted corolla abscission during a period when pollen grains are viable and the stigma is receptive. In addition, corolla abscission significantly increased the pollen deposition and seed setting rate. Our results demonstrate that nectar robbing contributes to enhancing seed production and positively and indirectly impacts the reproductive success of S. officinale. This mechanism involved the movement of anthers and indirect participation by nectar robbers, which was rarely investigated. Considering the multiple consequences of nectar robbing, understanding the impact of nectar robbers on plant reproduction is essential to comprehend the evolutionary importance of relationships between plants and their visitors.

Dracula’s mistress: removal of blood-red floral nectar results in secretion of more nectar

Background and aims – Flowers of Jaltomata quipuscoae (Solanaceae) secrete blood-red nectar that serves as an energy reward and possible attractant to pollinators. The purposes of this study were to determine whether simulated pollinator visits (manual removal of nectar) stimulates replenishment of nectar, and report the pattern of nectar presentation during the lifespan of the flower. Methods – For the nectar replenishment experiments flowers were paired: each pair of flowers was selected to be on the same plant and at the same developmental stage. From all 62 flowers nectar was removed and discarded (not measured) at time zero. Then, over a period of eight hours, the nectar of one flower was measured four times, i.e., every two hours, while nectar of the paired control flower was measured only at the end of the eight-hour period. In the nectar dynamics experiment five sets of flowers received different treatments: flowers were unmanipulated for zero, one, two, three or four days and then nectar was removed once every day. The volume of nectar produced and concentration of sugar in the nectar were recorded at each extraction for both studies.Key results – In the nectar replenishment study significantly higher nectar volume and consequently significantly higher total sugar content was present in the experimental nectar-extracted flowers. In the nectar dynamics study, nectar was produced starting on day one or two, continuously through the life of the open flowers until one or two days before the corolla senesced. Delay of nectar removal from different flower sets for zero, one, two, three or four days resulted in a linear increase in nectar volume and total nectar sugar production, and had little or no effect on the cumulative (life of the flower) nectar production. Floral longevity, seven to ten days, was not affected by a single removal of nectar each day.Conclusions – The floral nectary of J. quipuscoae responded to nectar removal by secreting more nectar, and thus more total sugar (not a higher concentration of sugar) than was secreted by control flowers. In flowers from which nectar was not removed, nectar volume and thus total sugar secreted continued to accumulate linearly, suggesting that reabsorption of nectar either does not occur or is slow relative to the rate of secretion. The more we (or pollinators) take, the more the flowers make: the volume of nectar and sugar production increase if nectar is removed frequently but not if nectar is removed infrequently.

Flower trade-offs derived from nectar investment in female reproduction of two Nicotiana species (Solanaceae)

ABSTRACT Animal-pollinated flowers may orient resources for competing activities, such as nectar production for attracting flower visitors but then saving nectar (through inhibiting nectar production or by final resorption) for the subsequent maturation of fruits and seeds. Nectar production is continuous in Nicotiana longiflora and N. alata after flower opening, but early nectar removal reduces total secreted nectar. Resource trade-off between nectar investment and seed production were experimentally assessed in manually pollinated flowers experiencing different numbers of repeated nectar removals, while controlling for maternal effects. We expected that flowers with less nectar secretion produce larger seed sets. The results showed that for both species the earlier the nectar removal during flower anthesis, the lower the total nectar secreted and the higher the mass of seeds produced. This general pattern was clearer for N. longiflora. The link between decreased nectar production and the subsequent increase in the seed set implies that resources are limited. Consequently, nectar savings during the pollination process through early nectar removal by pollinators can be interpreted as a trade-off between resources secreted by flowers for pollinator attraction and those utilized during fruit and seed maturation.

Costs and benefits of alternative food handling tactics help explain facultative exploitation of pollination mutualisms.

Many mutualisms are taken advantage of by organisms that take rewards from their partners but provide no benefit in return. In the absence of traits that limit exploitation, facultative exploiters (partners that can either exploit or cooperate) are widely predicted by mutualism theory to choose an exploitative strategy, potentially threatening mutualism stability. However, it is unknown whether facultative exploiters choose to exploit, and, if so, make this choice because it is the most beneficial strategy for them. We explored these questions in a subalpine plant-insect community in which individuals of several bumble bee species visit flowers both "legitimately" (entering via the flower opening, picking up and depositing pollen, and hence behaving mutualistically) and via nectar robbing (creating holes through corollas or using an existing hole, bypassing stigmas and anthers). We applied foraging theory to (1) quantify handling costs, benefits and foraging efficiencies incurred by three bumble bee species as they visited flowers legitimately or robbed nectar in cage experiments, and (2) determine whether these efficiencies matched the food handling tactics these bee species employed in the field. Relative efficiencies of legitimate and robbing tactics depended on the combination of bee and plant species. In some cases (Bombus mixtus visiting Corydalis caseana or Mertensia ciliata), the robbing tactic permitted more efficient nectar removal. As both mutualism and foraging theory would predict, in the field, B.mixtus visiting C.caseana were observed more frequently robbing than foraging legitimately. However, for Bombus flavifrons visiting M.ciliata, the expectation from mutualism theory did not hold: legitimate visitation was the more efficient tactic. Legitimate visitation to M.ciliata was in fact more frequently observed in free-flying B.flavifrons. Free-flying B.mixtus also frequently visited M.ciliata flowers legitimately. This may reflect lower nectar volumes in robbed than unrobbed flowers in the field. These results suggest that a foraging ecology perspective is informative to the choice of tactics facultative exploiters make. In contrast, the simple expectation that exploiters should always have an advantage, and hence could threaten mutualism persistence unless they are deterred or punished, may not be broadly applicable.

Consequences of secondary nectar robbing for male components of plant reproduction.

Organisms engage in multiple species interactions simultaneously. While pollination studies generally focus on plants and pollinators exclusively, secondary robbing, a behavior that requires other species (primary robbers) to first create access holes in corollas, is common. It has been shown that secondary robbing can reduce plants' female fitness; however, we lack knowledge about its impact on male plant fitness. We experimentally simulated primary and secondary robbing in the monocarpic perennial Ipomopsis aggregata (Polemoniaceae), quantifying indirect effects on pollinator-mediated pollen (dye) donation. We also assessed whether continual nectar removal via the floral opening has similar effects on hummingbird-pollinator behavior as continual secondary robbing through robber holes. We found no significant indirect effects of secondary robbing on a component of Ipomopsis male fitness. Although robbing did reduce pollen (dye) donation due to avoidance of robbed plants by pollinating hummingbirds, pollen donation did not differ between the two robbing treatments. The effects of secondary robbing on hummingbird behavior resembled effects of chronic nectar removal by pollinators. Our results indicate that hummingbird pollinators may use a combination of cues, including cues given by the presence or absence of nectar, to make foraging decisions. Combined with prior research, this study suggests that secondary robbing is less costly to a component of male fitness than to female fitness in Ipomopsis, broadening our knowledge of the overall costs of mutualism exploitation to total plant fitness.

Solving the puzzle of yeast survival in ephemeral nectar systems: exponential growth is not enough.

Flower nectar is a sugar-rich ephemeral habitat for microorganisms. Nectar-borne yeasts are part of the microbial community and can affect pollination by changing nectar chemistry, attractiveness to pollinators or flower temperature if yeast population densities are high. Pollinators act as dispersal agents in this system; however, pollination events lead potentially to shrinking nectar yeast populations. We here examine how sufficiently high cell densities of nectar yeast can develop in a flower. In laboratory experiments, we determined the remaining fraction of nectar yeast cells after nectar removal, and used honeybees to determine the number of transmitted yeast cells from one flower to the next. The results of these experiments directly fed into a simulation model providing an insight into movement and colonization ecology of nectar yeasts. We found that cell densities only reached an ecologically relevant size for an intermediate pollination probability. Too few pollination events reduce yeast inoculation rate and too many reduce yeast population size strongly. In addition, nectar yeasts need a trait combination of at least an intermediate growth rate and an intermediate remaining fraction to compensate for highly frequent decimations. Our results can be used to predict nectar yeast dispersal, growth and consequently their ecological effects.

Effect of mutualistic and antagonistic bees on floral resources and pollination of a savanna shrub

Since Darwin, cheaters have been described in plant-pollinator mutualisms. Bignoniaceae species have a wide interaction network with floral visitors, and most of those interactions are established with cheaters. Thus, our objective was to determine which role each floral visitor plays in a system composed by bees and a Bignoniaceae savanna species. So, here we described the bees’ behaviour and defined experimentally who are the mutualists and cheaters, we described the temporal sequence of interactions, quantified pollen and nectar removal, and checked for the potential effect of robbery damages on pollinator behaviour. Pollinators visited a small number of flowers, mainly in the early morning, while the most frequent cheaters (robbers and thieves) visited the flowers throughout the day, increasing visitation at midmorning, when pollinators had already visited the flowers. We considered medium-sized bees as pollinators, small bees acted only as cheaters, not contributing to seed production. Pollen thieves reduced the amount of male gametes available for pollination, while nectar thieves and robbers were associated with nectar depletion. We did not find any significant difference in the number of pollen grains deposited on the stigmas of flowers with and without robbery damages. In conclusion, when pollinators visit J. caroba flowers in the early morning, there might be a smaller competition pressure among visitors due to the greater amount of resources available, especially in recently opened flowers, and due to the low frequency of cheaters visits, which probably prevents a major negative impact of cheaters on pollination and plant reproduction in this species.

Effect of Nectar Reabsorption on Plant Nectar Investment in <I>Cerasus cerasoides</I>

Flowering progress, floral morphology and nectar characteristics of Cerasus cerasoides were investigated from November 2011 to January 2012 in Kunming, Yunnan, China. We found that nectar removal had a positive effect on nectar production. The phenomenon of nectar reabsorption in C. cerasoides occurred at the end of the floral lifespan, on the tenth day after anthesis when allowing for nectar accumulation. A flower reabsorbs nectar when it has not been foraged, with the reabsorbed sugar content accounting for about 34% of the maximum sugar content. Therefore, nectar reabsorption can only reclaim a part of the energy allocated for nectar production.

Quantifying direct vs. indirect effects of nectar robbers on male and female components of plant fitness

Summary Plants interact simultaneously with both mutualists and antagonists. While webs of plant–animal interactions in natural systems can be highly complex, most interactions can be simplified into those that are either direct (mediated through pairwise interactions) or indirect (mediated through third‐party species). Mechanistic studies of the direct and indirect pathways by which foliar herbivores affect plants have been well explored; however, mechanistic explorations of how floral herbivores, such as nectar robbers, affect total plant fitness via direct vs. indirect pathways have received less attention. The goal of this study was to assess the importance of direct vs. pollinator‐mediated indirect effects of a floral antagonist on female and male components of plant fitness. We focused on the hummingbird‐pollinated plant scarlet gilia, Ipomopsis aggregata, which is nectar‐robbed by the bumblebee Bombus occidentalis. Prior studies have found evidence for pollinator‐mediated indirect effects of robbing on female and male components of I. aggregata fitness, but the mechanisms by which these indirect effects occur, and experimental evidence supporting or refuting direct effects of robbing, have been lacking. We found no evidence for direct effects of robbing on plant fitness. Robbers did not act as pollinators of I. aggregata nor did they directly affect seed production by making nectar‐robber holes or removing nectar in hand‐pollinated flowers. Moreover, robbing had no direct effect on pollen production per flower or the ability of pollen from robbed flowers to sire seeds in hand pollinations. However, nectar robbing had indirect effects on plant reproduction mediated through per‐visit pollinator effectiveness at depositing pollen in robbed vs. unrobbed flowers. A simple model of a plant‐robber‐pollinator system suggested that robbing effects in general may occur through more indirect mechanisms when nectar removal by robbers is high relative to nectar replenishment, and that compensation for robbing is then more profitable through the production of additional flowers. Synthesis. Our results highlight the importance of indirect effects in mediating the fitness consequences of species interactions.

Floral nectar production and nectary structure of a bee‐pollinated shrub from Neotropical savanna

Biotic pollination is critical for tropical ecosystem functioning, and nectar plays an essential role as it represents the main trophic resource for pollinators. Nevertheless, little is known about the mechanisms that underlie its production, which is essential for understanding the basis of nectar-mediated interactions in ecological and evolutionary approaches. Therefore, this study explores the relationship between the nectar secretion pattern and nectary functional changes in Anemopaegma album, a bee-pollinated species. We analysed the pattern of nectar production under field conditions and investigated floral nectary structural changes in two different developmental stages using light, transmission and scanning electron microscopy. We measured 30.95 ± 23.02 μl (mean ± SD, n = 30) of nectar accumulated inside the nectar chamber (29.26 ± 3.48% sucrose equivalents) at the moment of flower opening. Nectar removal did not influence the pattern of floral nectar production in terms of volume or total sugar but reduced the concentration of the nectar produced during the first 24 h of anthesis. The nectary consisted of an epidermis, a nectary parenchyma and a subnectary parenchyma supplied only by phloem. Starch grains decreased in size and abundance from the subnectary parenchyma toward the epidermis. We observed the degradation of starch grains and incorporation of amyloplasts into vacuoles at the pre-anthesis stage as well as the transformation of amyloplasts into elaioplasts during anthesis. Nectar secretion was continuous during the A. album flower life span, which was related to the functional features of its floral nectary, especially the presence of starch stored in the parenchyma.

Floral biology and nectar production dynamics of Pachira aquatica Aubl. (Malvaceae) in the eastern Amazon

Pachira aquatica is a Neotropical tree of economic importance for local communities, although little is known about its flower biology especially flower rewards. This study aimed to analyze some aspects of flower biology of this species, focusing on nectar production dynamics We measured nectar production and analyzed the effect of nectar removal and cross-pollination on sugar production and standing crop (the amount of nectar present in a flower exposed to pollination at a given moment). We found that P. aquatica has large, brush-type, perfect flowers, with white colored petals, red stamens and a strong floral scent. Flowers are protandrous and dichogamous. Pollen viability is about 96%. Anthesis is nocturnal and asynchronous. The nectar is relatively abundant (99.8 ± 118.5 μL) and diluted (15.2 ± 4.7% p/p) and its production increases in the morning period. Neither nectar removal nor cross-pollination affected sugar production. Standing crop was not significantly different from the control, indicating that there is probably a low visitation rate. Both flower and nectar production characteristics indicate that this species has the potential to be visited by different flower visitors, especially bats, birds and bees.

Producción de néctar y flores como rasgos compensatorios al robo de néctar en Bouvardia ternifolia (Rubiaceae): experimentos de campo

El néctar de flores polinizadas por colibríes es usualmente robado por animales no polinizadores, por ello se esperaría que plantas sometidas al robo de néctar presenten distintas estrategias que permitan mitigar los costos asociados. En este estudio, evaluamos la producción de néctar y flores como rasgos para mitigar el robo de néctar en la planta diestílica Bouvardia ternifolia (Rubiaceae) en el Parque Nacional la Malinche, Tlaxcala, México. Plantas de ambos morfos fueron sometidas a tres tratamientos: (1) tratamiento de remoción de néctar, (2) tratamiento sin remoción y (3) tratamiento control (plantas sin exclusión ni extracción de néctar). Durante el periodo de fl oración, cuantifi camos semanalmente el volumen de néctar (15 fl ores/planta) y el número de fl ores producidas por planta. Polinizamos manualmente las flores focales y los frutos producidos se recolectaron y sus semillas contadas. Las flores con y sin remoción de néctar produjeron similar recompensa; contrario a los pequeños volúmenes producidos en flores control. Las flores del morfo pin mostraron mayores volúmenes y concentraciones de néctar que las thrum. No encontramos efecto de los tratamientos sobre la producción de flores en ambos morfos. Las flores con y sin remoción de néctar produjeron más semillas que las flores control. Nuestros resultados sugieren que Bouvardia puede sobrecompensar el néctar robado, pero no las flores; sin afectar el número de semillas producidas.

Nectar Production by InvasiveLantana camaraand EndemicL. peduncularisin the Galápagos Islands

Measurements of nectar volume and sugar concentration along two elevational gradients, in flower exclusion experiments, and over a diurnal cycle of nectar production were compared for invasive Lantana camara and endemic Lantana peduncularis in the Galapagos Islands during the dry season. Both species show the same pollination syndrome and are pollinated by Lepidoptera. Lantana camara flowers had a higher nectar volume than L. peduncularis flowers at every elevation and higher total sugar content. However, nectar in L. peduncularis flowers was much more concentrated than in L. camara flowers at lower elevations. The differences in nectar production between Lantana species seemed to be intrinsic and related to contrasting strategies to cope with drought. Nectar volume of unbagged flowers of L. camara was lower than that of bagged flowers at sunrise, which was probably related to consumption of nectar by nocturnal Lepidoptera. Nectar removal by floral visitors had a pronounced effect on total amount of nectar secreted by L. camara flowers but sugar concentration did not vary significantly. Our results suggest that L. camara may compete with L. peduncularis for pollinators.

Beyond the pollination syndrome: nectar ecology and the role of diurnal and nocturnal pollinators in the reproductive success of Inga sessilis (Fabaceae)

Inga species present brush-type flower morphology allowing them to be visited by distinct groups of pollinators. Nectar features in relation to the main pollinators have seldom been studied in this genus. To test the hypothesis of floral adaptation to both diurnal and nocturnal pollinators, we studied the pollination ecology of Inga sessilis, with emphasis on the nectar secretion patterns, effects of sequential removals on nectar production, sugar composition and the role of diurnal and nocturnal pollinators in its reproductive success. Inga sessilis is self-incompatible and pollinated by hummingbirds, hawkmoths and bats. Fruit set under natural conditions is very low despite the fact that most stigmas receive polyads with sufficient pollen to fertilise all ovules in a flower. Nectar secretion starts in the bud stage and flowers continually secreting nectar for a period of 8 h. Flowers actively reabsorbed the nectar a few hours before senescence. Sugar production increased after nectar removal, especially when flowers were drained during the night. Nectar sugar composition changed over flower life span, from sucrose-dominant (just after flower opening, when hummingbirds were the main visitors) to hexose-rich (throughout the night, when bats and hawkmoths were the main visitors). Diurnal pollinators contributed less than nocturnal ones to fruit production, but the former were more constant and reliable visitors through time. Our results indicate I.sessilis has floral adaptations, beyond the morphology, that encompass both diurnal and nocturnal pollinator requirements, suggesting a complementary and mixed pollination system.

Functional aspects of floral nectar secretion of Ananas ananassoides, an ornithophilous bromeliad from the Brazilian savanna.

Several members of Bromeliaceae show adaptations for hummingbird pollination in the Neotropics; however, the relationships between floral structure, nectar production, pollination and pollinators are poorly understood. The main goal of this study was to analyse the functional aspects of nectar secretion related to interaction with pollinators by evaluating floral biology, cellular and sub-cellular anatomy of the septal nectary and nectar composition of Ananas ananassoides, including an experimental approach to nectar dynamics. Observations on floral anthesis and visitors were conducted in a population of A. ananassoides in the Brazilian savanna. Nectary samples were processed using standard methods for light and transmission electron microscopy. The main metabolites in nectary tissue were detected via histochemistry. Sugar composition was analysed by high-performance liquid chromatography (HPLC). The accumulated nectar was determined from bagged flowers ('unvisited'), and floral response to repeated nectar removal was evaluated in an experimental design simulating multiple visits by pollinators to the same flowers ('visited') over the course of anthesis. The hummingbirds Hylocharis chrysura and Thalurania glaucopis were the most frequent pollinators. The interlocular septal nectary, composed of three lenticular canals, extends from the ovary base to the style base. It consists of a secretory epithelium and nectary parenchyma rich in starch grains, which are hydrolysed during nectar secretion. The median volume of nectar in recently opened 'unvisited' flowers was 27·0 µL, with a mean (sucrose-dominated) sugar concentration of 30·5 %. Anthesis lasts approx. 11 h, and nectar secretion begins before sunrise. In 'visited' flowers (experimentally emptied every hour) the nectar total production per flower was significantly higher than in the 'unvisited' flowers (control) in terms of volume (t = 4·94, P = 0·0001) and mass of sugar (t = 2·95, P = 0·007), and the concentration was significantly lower (t = 8·04, P = 0·0001). The data suggest that the total production of floral nectar in A. ananassoides is linked to the pollinators' activity and that the rapid renewal of nectar is related to the nectary morphological features.