Nectar Sugar Concentration Research Articles

Food Limitation Affects Parasite Load and Survival of Bombus impatiens (Hymenoptera: Apidae) Infected With Crithidia (Trypanosomatida: Trypanosomatidae).

Bumble bees (genus Bombus) are globally important insect pollinators, and several species have experienced marked declines in recent years. Both nutritional limitation and pathogens may have contributed to these declines. While each of these factors may be individually important, there may also be synergisms where nutritional stress could decrease pathogen resistance. Understanding interactions between bumble bees, their parasites, and food availability may provide new insight into the causes of declines. In this study, we examined the combined impacts of pollen and nectar limitation on Crithidia, a common gut parasite in Bombus impatiens Cresson. Individual worker bees were inoculated with Crithidia and then assigned in a factorial design to two levels of pollen availability (pollen or no pollen) and two nectar sugar concentrations (high [30%] or low [15%] sucrose). We found that lack of pollen and low nectar sugar both reduced Crithidia cell counts, with the most dramatic effect from lack of pollen. Both pollen availability and nectar sugar concentration were also important for bee survival. The proportion of bees that died after seven days of infection was ∼25% lower in bees with access to pollen and high nectar sugar concentration than any other treatment. Thus, nectar and pollen availability are both important for bee survival, but may come at a cost of higher parasite loads. Our results illustrate the importance of understanding environmental context, such as resource availability, when examining a host-parasite interaction.

Sugar concentration in nectar: a quantitative metric of crop attractiveness for refined pollinator risk assessments.

Those involved with pollinator risk assessment know that agricultural crops vary in attractiveness to bees. Intuitively, this means that exposure to agricultural pesticides is likely greatest for attractive plants and lowest for unattractive plants. While crop attractiveness in the risk assessment process has been qualitatively remarked on by some authorities, absent is direction on how to refine the process with quantitative metrics of attractiveness. At a high level, attractiveness of crops to bees appears to depend on several key variables, including but not limited to: floral, olfactory, visual and tactile cues; seasonal availability; physical and behavioral characteristics of the bee; plant and nectar rewards. Notwithstanding the complexities and interactions among these variables, sugar content in nectar stands out as a suitable quantitative metric by which to refine pollinator risk assessments for attractiveness. Provided herein is a proposed way to use sugar nectar concentration to adjust the exposure parameter (with what is called a crop attractiveness factor) in the calculation of risk quotients in order to derive crop‐specific tier I assessments. This Perspective is meant to invite discussion on incorporating such changes in the risk assessment process. © 2016 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Floral specialization for different pollinators and divergent use of the same pollinator among co-occurringImpatiensspecies (Balsaminaceae) from Southeast Asia

Floral variation among closely related species is thought to often reflect differences in pollination systems. Flowers of the large genus Impatiens are characterized by extensive variation in colour, shape and size and in anther and stigma positioning, but studies of their pollination ecology are scarce and most lack a comparative context. Consequently, the function of floral diversity in Impatiens remains enigmatic. This study documents floral variation and pollination of seven co-occurring Impatiens spp. in the Southeast Asian diversity hotspot. To assess whether floral trait variation reflects specialization for different pollination systems, we tested whether species depend on pollinators for reproduction, identified animals that visit flowers, determined whether these visitors play a role in pollination and quantified and compared key floral traits, including floral dimensions and nectar characteristics. Experimental exclusion of insects decreased fruit and seed set significantly for all species except I. muscicola, which also received almost no visits from animals. Most species received visits from several animals, including bees, birds, butterflies and hawkmoths, only a subset of which were effective pollinators. Impatiens psittacina, I. kerriae, I. racemosa and I. daraneenae were pollinated by bees, primarily Bombus haemorrhoidalis. Impatiens chiangdaoensis and I. santisukii had bimodal pollination systems which combined bee and lepidopteran pollination. Floral traits differed significantly among species with different pollination systems. Autogamous flowers were small and spurless, and did not produce nectar; bee-pollinated flowers had short spurs and large floral chambers with a wide entrance; and bimodally bee- and lepidopteran-pollinated species had long spurs and a small floral chamber with a narrow entrance. Nectar-producing species with different pollination systems did not differ in nectar volume and sugar concentration. Despite the high frequency of bee pollination in co-occurring species, individuals with a morphology suggestive of hybrid origin were rare. Variation in floral architecture, including various forms of corolla asymmetry, facilitates distinct, species-specific pollen-placement on visiting bees. Our results show that floral morphological diversity among Impatiens spp. is associated with both differences in functional pollinator groups and divergent use of the same pollinator. Non-homologous mechanisms of floral asymmetry are consistent with repeated independent evolution, suggesting that competitive interactions among species with the same pollination system have been an important driver of floral variation among Impatiens spp.

English

Insects are a major mode of banana Xanthomonas wilt (XW) spread. High insect activity has been blamed for the high XW incidence in ‘Kayinja’ (ABB-genome) dominated banana landscapes across east and central Africa. ‘Kayinja’ male bud nectar composition reportedly contributes to high insect activity. The variation in nectar composition with agro-ecological zones and banana cultivars and its influence on the number of visiting insects in Rwanda were assessed. Three male buds were collected per cultivar for nectar extraction and analysis using a high performance liquid chromatography. Nectar volume and sugar concentrations varied (P<0.001) across 27 banana cultivars, annual seasons and agro-ecological zone. The highest nectar volume was recorded among the East African highland cooking cultivars (AAA-genome) in the high altitude site and the short-heavy rainy season. Nectar contained three sugars: glucose, fructose and sucrose, though hexose (glucose and fructose) was dominant. The three sugars varied significantly (P<0.001) within each cultivar. The total nectar-sugar concentration ranged from 2.3–32%, with the highest among dessert cultivars ‘Kamaramasenge’ (AAB-genome) and ‘Gisukari’ (AAA-genome). No strong correlation occurred between insect population and total nectar sugar concentration or nectar volume. Insect populations were rather influenced by the weather conditions, the long rainy season characterized by moderate well distributed rainfall recording the highest insect populations as compared to the short rainy season (with heavy rainfall) and the dry seasons. Key words: Banana, insects, nectar, vectors, Xanthomonas campestris pv. musacearum

Floral nectary, nectar production dynamics, and floral reproductive isolation among closely related species of Pedicularis.

Floral nectar is thought to be one of the most important rewards that attract pollinators in Pedicularis; however, few studies have examined variation of nectary structure and/or nectar secretion in the genus, particularly among closely related species. Here we investigated nectary morphology, nectar quality, and nectar production dynamics in flowers of Pedicularis section Cyathophora. We found a conical floral nectary at the base of the ovary in species of the rex-thamnophila clade. Stomata were found on the surface of the nectary, and copious starch grains were detected in the nectary tissues. In contrast, a semi-annular nectary was found in flowers of the species of the superba clade. Only a few starch grains were observed in tissues of the semi-annular nectary, and the nectar sugar concentration in these flowers was much lower than that in the flowers of the rex-thamnophila clade. Our results indicate that the floral nectary has experienced considerable morphological, structural, and functional differentiation among closely related species of Pedicularis. This could have affected nectar production, leading to a shift of the pollination mode. Our results also imply that variation of the nectary morphology and nectar production may have played an important role in the speciation of sect. Cyathophora.

Early spring floral foraging resources for pollinators in wet heathlands in Belgium

In temperate regions, foraging resources for pollinating insects are particularly important in early spring, especially for social insects like bumblebees that are initiating colonies. Heathlands, protected open habitats under EU law, provide floral resources (pollen and nectar) for a range of pollinating insects. In early spring, in Belgian heathlands, only two floral resources are available: willows Salix spp. (Salicaceae) and bilberry Vaccinium myrtillus (Ericaceae). Our objective was to assess whether these two plant species provide quantitative and qualitative resources during early spring. We examined the springtime activity of flower visitors on both S. x multinervis and V. myrtillus flowers in relation to sugar concentration and composition in nectar as well as composition of polypeptides and amino acids in pollen. The chemical composition of pollen differed significantly between the two plant species. Salix x multinervis offered pollen with higher polypeptide and essential amino acid contents than V. myrtillus. However, nectar quantities of V. myrtillus flowers were relatively high compared to S. x multinervis. During the overlapping flowering period of the two plant species, flower visitors seemed to favor high quality and easily accessible pollen of S. x multinervis species and visited V. myrtillus mainly for nectar resources.

Flower colour and visitation rates of Costus arabicus support the ‘bee avoidance’ hypothesis for red‐reflecting hummingbird‐pollinated flowers

Summary Floral colour mediates plant–pollinator interactions by often signalling floral resources. In this sense, hummingbird‐pollinated flowers are frequently red‐coloured, and there are two tentative hypotheses to explain this pattern: 1. hummingbirds are attracted to red due its easier detection and 2. bees are sensorially excluded from red flowers. The second hypothesis is based on bees’ red colour blindness, which lead them to be less frequent and less important than hummingbirds as pollinators of red‐reflecting flowers. Here, we untangled the role of different flower traits mediating plant–pollinator interactions and empirically tested the above hypotheses. We chose Costus arabicus due to its synchronopatric white‐ and pink‐flowered individuals and its bee and hummingbird pollination system. Although pink flowers are not totally achromatic as pure red ones, they show an achromaticity degree that could drive bee exclusion. Specifically, we tested whether differences on red reflectance work attracting hummingbirds or excluding bees and the consequent implications for the plant's reproduction. Flower colour morphs of C. arabicus do differ neither in morphology nor in nectar sugar content. Moreover, white and pink flowers can be discriminated by the bees’ and hummingbirds’ colour vision system. Both groups are able to discriminate the red colour variation morph on the flower petals, the white flowers being more easily detected by bees and the pink flowers by hummingbirds. Bees preferentially visited the white flowers, whereas hummingbirds visited both colours at the same rate – both patterns corroborating the second hypothesis. Pollen loads deposited on stigmas did not differ between flower colour morphs, indicating that bees and hummingbirds play a similar role in the overall pollen deposition. However, bees are more likely to self‐pollinate than hummingbirds. Self‐pollination limits C. arabicus reproduction, and red‐reflecting flowers may be better pollinated by discouraging bee visitation. Therefore, the intraspecific colour variation is driving flowers to show colour‐related different levels of generalization. Our results support the ‘bee avoidance’ rather than the ‘hummingbird preference’ hypothesis. Sensory exclusion of bees seems to be the pressure for red‐reflecting flowers evolution, driving specialization in hummingbird‐pollinated flowers due to the costs of bee pollination on plant reproduction.

Comparative effects of two species of floricolous <em>Metschnikowia</em> yeasts on nectar

Canto, A., Herrera, C.M., Garcia, I.M., Garcia, M., Bazaga, P. 2015. Comparative effects of two species of floricolous Metschnikowia yeasts on nectar. Anales Jard. Bot. Madrid 72(1): e019 Nectar yeast communities in southern Spain are dominated by two closely-related species, Metschnikowia reukaufii Pitt & M.W. Mill. and M. gruessii Gim.-Jurado (Ascomycota, Saccharomycetales), although they tend to be distributed differentially across different host plants. We explore here the possibility that the two yeasts play different functional roles in floral nectar by differing in their impact on sugar concentra- tion and composition of nectar. Experiments were undertaken under controlled conditions using bumblebees caught foraging on the flowers of two different host plants each of which is known to harbor pre- dominantly one of the two yeasts. Bumblebees were used as sources of inocula to obtain two groups of samples from the nectar of Helleborus foetidus L. (Ranunculaceae): nectar samples inoculated with M. gruessii and samples inoculated with M. reukaufii. Metschnikowia gruessii was poorly represented in nectar samples, while M. reukaufii was by far the most common and had the highest cell density. Although the two yeasts caused relatively similar changes in nectar sugar composition, which involved increasing fructose and decreasing sucrose proportions, they marginally differed in their quantitative impact on total nectar sugar concentration. Results suggest that differential yeast occurrence across host plants may lead to yeast specialization and modify the outcomes of the plant-pollinator interface.

In response: Challenges for future risk assessments--A governmental perspective.

In response: Challenges for future risk assessments--A governmental perspective.

Reproductive biology of Pachira aquatica Aubl. (Malvaceae: Bombacoideae): a tropical tree pollinated by bats, sphingid moths and honey bees

AbstractWe investigated the reproductive biology, including the floral biology, pollination biology, breeding system and reproductive success, of Pachira aquatica, a native and dominant tropical tree of fresh water wetlands, throughout the coastal plain of the Gulf of Mexico. The flowers present nocturnal anthesis, copious nectar production and sugar concentration (range 18–23%) suitable for nocturnal visitors such as bats and sphingid moths. The main nocturnal visitors were bats and sphingid moths while bees were the main diurnal visitors. There were no differences in legitimate visitation rates among bats, moths and honey bees. Bats and honey bees fed mainly on pollen while moths fed on nectar, suggesting resource partitioning. Eight species of bats carried pollen but Leptonycteris yerbabuenae is probably the most effective pollinator due to its higher pollen loads. The sphingid moths Manduca rustica, Cocytius duponchel and Eumorpha satellitia were recorded visiting flowers. Hand pollination experiments indicated a predominant outcrossing breeding system. Open pollination experiments resulted in a null fruit set, indicating pollen limitation; however, mean reproductive success, according to a seasonal census, was 17 ± 3%; these contrasting results could be explained by the seasonal availability of pollinators. We conclude that P. aquatica is an outcrossing species with a pollination system originally specialized for bats and sphingid moths, which could be driven to a multimodal pollination system due to the introduction of honey bees to tropical America.

Biología floral de <i>Passiflora foetida</i> (Passifloraceae)

Un experimento reproductivo muestra que Passiflora foetida es autocompatible. Observaciones de las características florales y de los visitantes durante la antesis, más el análisis del polen transportado, permitieron identificar el síndrome floral (melitofilia) y las funciones de cada visitante. La antesis ocurre desde las 6 hasta las 11 hs. Se identificaron 3 fases ílorales: 1) estigmas por encima de las anteras, 2) estigmas a la altura de las anteras, 3) estigmas por encima de las anteras; los radii, los pétalos y los sépalos se incurvan. Los estigmas están receptivos durante toda la antesis. La concentración de azúcares del néctar es 34 %. El color predominante en el espectro visible es el blanco. En el espectro UV, los estambres y el gineceo contrastan con el limen y el an droginóforo; pueden ser una - guía de néctar. Tres· especies de himenópter-os fueron los· visitantes más frecuentes y constantes: Ptiloglossa larsata (Colletidae) siempre contactan las anteras y los estigmas cuando liban, transportan un alto porcentaje de polen de P. foetida y visitan flores en fase 1 y 2; pue den ser considerados los principales polinizadores. Pseudilugochloropsis sp. (Halictidae) raramente contactan las anteras o los estigmas cuando perforan el limen para acceder al néctar y visitan flores en fase 2 y 3; son ladrones de néctar que raramente polinizan. Augochlorella sp. (Halictidae) recolectan polen sin tocar los estigmas y visitan flores en fase 2 y 3; son hurtadores de polen.

Honeybee Visiting and Floral Nectar Characteristics of Styrax japonicus Sieb. & Zucc

This study was conducted to prove possibility of honey tree, which analyzed the visited number of honeybees, secreted nectar volume, nectar sugar content and amino acid in addition to estimating honey quantities that can ultimately reap in flowers of Styrax japonicus Sieb. & Zucc.. The surveyed tree’s flowers bloom during 12 days and maximum blooming period of flowers was on 23 rd to 25 th May in 2013. Honeybee visited flowers in priority and visited number of honeybee per flowering lateral bunch can be assumed 290 honeybees for a day. Honeybee visiting was concentrated at around 10~11 a.m.. On average, nectar volume secreted by nectary was 1.13 ul from one flower and nectar concentration (w/w %) presented 39.6%. Sugar content were calculated at 71.0 ug per flower which was estimated by multiplying secreted nectar volume (ul/flower) by nectar sugar (ug/ul). The minimum estimate of honey harvest for official tree (15 years, Height = 3m, Diameter at breast height = 12cm) in this study was 3,032 mg. Result of amino acid content ratio showed that Proline, Glutamate, Hydroproline, Serine, Asparagine were more abundant than others. Especially, Proline percentages (40.4%) were highest among the other amino acids. Finally, the surveyed tree is considered as possible honey plant because of its nectar characteristics and honeybee visiting. Honey is made of nectar sugar as well as by digestive system of honeybee, therefore a more associated study is necessary to analyze free sugar component in nectar and accurately presume to harvest honey quantity.

Diurnal versus nocturnal pollination success in Billbergia horrida Regel (Bromeliaceae) and the first record of chiropterophily for the genus.

Billbergia horrida is endemic of the Atlantic Forest fragments in southeastern Brazil and characterized by flowers with typical traits for pollination by nocturnal animals. Although the majority of Billbergia species rely on diurnal pollination by hummingbirds, B. horrida is also visited by bats and this study evidences for the first time the occurrence of chiropterophily within the genus. The role of different groups of pollinators on the reproductive success of B. horrida was evaluated, as well as the correlation of nectar features in sustaining these animals during different periods of the day. Bats contributed to 82.1% of fruit set of B. horrida. Hummingbirds, in turn, contributed to only 10% of fruit set, and were poorly related to the reproductive success of this species. Amounts of nectar production and sugar concentration were similar to those of other chiropterophilous bromeliads and only the nectar volume changed significantly throughout the period of flower availability. Recurring visits by hummingbirds were probably because the flowers of B. horrida were open for 24h, offering energetic rewards for daytime visitors and due to the presence of other attractive bromeliad species growing at the same phorophyte and flowering at the same time.

Reward quality predicts effects of bird-pollinators on the reproduction of African Protea shrubs

Pollination syndromes predict the principal animal pollinators of plant species from floral traits. However, the existence of discrete pollination syndromes and the relevance of these syndromes for the effects of animal pollinators on plant reproduction are controversial and a quantitative, trait-based approach may refine the concept of pollination syndromes. Thus far, however, very few studies have simultaneously analysed the importance of signalling, accessibility and reward traits of flowers for the effects of animal pollinators on plant reproduction of multiple species. The genus Protea is an ideal study system because the members of this genus exhibit remarkable variation in functional traits and Protea species are visited by several guilds of animal pollinators, such as birds and insects. We experimentally investigated seven Protea species from the South African fynbos to assess variability in reproduction (seed set, seed mass, germination) in response to pollinator exclusion (full-exclusion, bird-exclusion) and hand-pollination (self-pollen, cross-pollen). To generalise the findings of the experiment, we conducted a meta-analysis of the effects of bird-exclusion on seed set of 14 Protea species, associating effect sizes of bird-pollination with signalling (inflorescence length and diameter), accessibility (inflorescence and style length) and reward traits (length of pollen presenter, nectar volume and sugar concentration). All Protea species were self-compatible, but only two species were to a small degree capable of autonomous selfing. Protea species varied in their dependence on animal pollinators, including species depending exclusively on birds, insects, or both for seed production. Protea species exhibited continuous variation in the effects of bird-pollinators on reproduction, challenging the accuracy of categorical pollination syndromes for predicting pollinator effects on plant reproduction. The meta-analysis showed that the quality of floral rewards, especially nectar sugar concentration, predicts the dependence of Protea reproduction on bird pollinators, whereas the signalling and accessibility traits tested in this study were not important. Beyond revealing new insights into the pollination biology of Protea species, our findings underscore the usefulness of experimental approaches on multiple plant species to test the effects of pollinator guilds on plant reproduction and contribute to a trait-based understanding of the functional determinants of plant–pollinator interactions.

Nectar sugars and bird visitation define a floral niche for basidiomycetous yeast on the Canary Islands.

BackgroundStudies on the diversity of yeasts in floral nectar were first carried out in the late 19th century. A narrow group of fermenting, osmophilous ascomycetes were regarded as exclusive specialists able to populate this unique and species poor environment. More recently, it became apparent that microorganisms might play an important role in the process of plant pollination. Despite the importance of these nectar dwelling yeasts, knowledge of the factors that drive their diversity and species composition is scarce.ResultsIn this study, we linked the frequencies of yeast species in floral nectars from various host plants on the Canary Islands to nectar traits and flower visitors. We estimated the structuring impact of pollination syndromes (nectar volume, sugar concentration and sugar composition) on yeast diversity.The observed total yeast diversity was consistent with former studies, however, the present survey yielded additional basidiomycetous yeasts in unexpectedly high numbers. Our results show these basidiomycetes are significantly associated with ornithophilous flowers. Specialized ascomycetes inhabit sucrose-dominant nectars, but are surprisingly rare in nectar dominated by monosaccharides.ConclusionsThere are two conclusions from this study: (i) a shift of floral visitors towards ornithophily alters the likelihood of yeast inoculation in flowers, and (ii) low concentrated hexose-dominant nectar promotes colonization of flowers by basidiomycetes. In the studied floral system, basidiomycete yeasts are acknowledged as regular members of nectar. This challenges the current understanding that nectar is an ecological niche solely occupied by ascomycetous yeasts.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-015-0036-x) contains supplementary material, which is available to authorized users.

Insect Pollinators and Productivity of Sweet Orange

Sweet orange which bears highly attractive flowers having high sugar concentration of nectar, with heavy pollens is not adapted for wind pollination. Therefore cross-pollination is accomplished by pollinators. The highest fruit retention % (1.67± 0.08%), fruit weight (118.93± 0.36 g) and yield (8.93± 0.17 kg/plant) were recorded from open pollination and it is significantly superior over both exclusive stingless bee pollination and pollinator exclusion. All the treatments were at par as regards fruit TSS, dry matter and ash %. Diverse pollinators influence fruit retention, fruit weight and productivity in comparison to single pollinator and pollinator exclusion. Nevertheless, single pollinator also enhances the productivity in comparison to pollinator exclusion.

Experimental evidence for specialized bird pollination in the endangered South African orchidSatyrium rhodanthumand analysis of associated floral traits

The bird pollination syndrome is characterized by red, unscented flowers with dilute nectar in long nectar tubes. However, the extent to which plants with such traits actually depend on birds for seed production is seldom determined experimentally, and traits such as colour and scent production are often assessed only subjectively. We documented bird pollination and quantified floral traits in the critically endangered Satyrium rhodanthum (Orchidaceae) from mistbelt grasslands in the summer-rainfall region of South Africa. Direct observations and motion trigger camera footage revealed amethyst sunbirds as the only pollinators, despite the presence of other potential pollinators. Experimental exclusion of sunbirds significantly reduced pollination and fruit set to near zero. Pollination success in naturally pollinated plants was close to 100% in one year, and fruit set varied from 23 to 64% in other years. Pollen transfer efficiency was 5.8%, which is lower than in related insect-pollinated species, probably due to a tendency of birds to wipe pollinaria from their beak. Flowers of S. rhodanthum only reflect light in the red range of the spectrum, and they produce only a few aliphatic and monoterpene scent compounds at comparatively low emission rates. Nectar volume and sugar concentration varied between 2.7 and 3.7 μL and 23.7 and 25.9%, respectively. We conclude that S. rhodanthum is highly specialized for pollination by sunbirds. Colour, scent and nectar characteristics differ from insect-pollinated Satyrium species and are consistent with those expected for bird-pollinated flowers, and may contribute to lack of visitation by other potential long-tongued pollinators. Habitat loss probably underlies the critically endangered conservation status of S. rhodanthum, but the specialization for pollination by a single bird species means that reproduction in this orchid is vulnerable to losses in surrounding communities of plants that subsidize the energetic requirements of sunbirds. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 177, 141–150.

Raising the sugar content--orchid bees overcome the constraints of suction feeding through manipulation of nectar and pollen provisions.

Unlike most other bees, the long-tongued orchid bees ingest nectar using suction feeding. Although long tongues allow exploitation of flowers with deep spurs, the energy intake rate is optimal at 10–20% lower nectar sugar concentrations compared to that of lapping bees. This constraint might be compensated by a higher digestive throughput. Additionally, orchid bees might evaporate water from regurgitated droplets of crop contents. We found male Euglossa championi (n = 10) and Euglossa dodsoni (n = 12) to regularly regurgitate droplets of crop content to the base of their proboscis, generating a fluid film between the proximal parts of the galeae, glossa and labial palps. Rhythmic movements of the proboscis may help to increase convection. There was a significant change in sugar concentration between the initially imbibed solution and the resulting crop content (P<0.05) and the time individual bees had engaged in this liquid exposure behavior was positively correlated with the resulting crop sugar concentration. Female Euglossa townsendi and Euglossa viridissima showed the same behavior. Additionally, they manipulated their nectar-enriched pollen provisions for extensive periods of time before deposition in brood cells. The deposited pollen loads (n = 14) showed a significantly higher sugar concentration than the sugar-water available to the bees (P<0.001). Thus, both male and female euglossines show behaviors that promote evaporative water loss from nectar. We suggest that the behaviors have evolved in concert with suction feeding on dilute nectar from deep floral tubes.

Nectaries and male-biased nectar production in protandrous flowers of a perennial umbellifer Angelica sylvestris L. (Apiaceae)

Nectar is the most common floral pollinator reward. In dichogamous species, floral nectar production rates can differ between sexual phases. We studied the structure of nectaries located on the stylopodium and nectar production in protandrous umbellifer Angelica sylvestris. Our study species produced nectar in both floral sexual phases. Nectar sugar concentration was low (on average 22 ± 11 %, mean ± SD) and the nectar hexose rich and composed of sucrose, glucose, fructose and a small amount of amino acids, including β-alanine, a non-protein amino acid. Although nectar composition and sugar concentration varied little between floral sexual phases, nectar production showed a threefold reduction during the stigma receptive period. This is in contrast to other studies of Apiaceae that have reported female-biased nectar production, but in the direction predicted by plant sexual selection theory, suggesting that in pollen-unlimited species, floral rewards mainly enhance male reproductive success. The structure of the nectary was similar at the two sexual stages investigated, and composed of a secretory epidermis and several layers of nectariferous and subsecretory parenchyma. The nectary cells were small, had large nuclei, numerous small vacuoles and dense, intensely staining cytoplasm with abundant endoplasmic reticulum, mitochondria and secretory vesicles. They contained abundant resin-like material that may potentially act as defence against microbes. Starch was rarely observed in the nectary cells, occurring predominantly at the female stage and mainly in guard and parenchyma cells in close proximity to stomata, and in subsecretory parenchyma. The main route of nectar release in A. sylvestris seems to be via modified stomata.

The potential for indirect effects between co‐flowering plants via shared pollinators depends on resource abundance, accessibility and relatedness

Co-flowering plant species commonly share flower visitors, and thus have the potential to influence each other's pollination. In this study we analysed 750 quantitative plant-pollinator networks from 28 studies representing diverse biomes worldwide. We show that the potential for one plant species to influence another indirectly via shared pollinators was greater for plants whose resources were more abundant (higher floral unit number and nectar sugar content) and more accessible. The potential indirect influence was also stronger between phylogenetically closer plant species and was independent of plant geographic origin (native vs. non-native). The positive effect of nectar sugar content and phylogenetic proximity was much more accentuated for bees than for other groups. Consequently, the impact of these factors depends on the pollination mode of plants, e.g. bee or fly pollinated. Our findings may help predict which plant species have the greatest importance in the functioning of plant-pollination networks.