Nectar production and the effect of its removal on total nectar sugar amount were determined by using sets of bagged flowers. All the species had a vascularized discoidal nectary surrounding the ovary base with numerous open stomata with a species-specific distribution. All nectar samples contained amino acids and sugars. Most species had sucrose-dominant nectars.
Flowers lasted a few hours. Nectar secretion began as soon as the flowers opened and lasted for a few hours in I. There was an increase of total sugar production after removals in I. Flower length was correlated with nectary size and total volume of nectar secreted, suggesting that structural constraints may play a major role in the determination of nectar traits of these species.
Floral nectar is widely known as the key reward offered by animal-pollinated plants to their pollen vectors Proctor et al. This exudate is secreted by nectaries, i. Sugars dominate the total solutes in floral nectar: Other compounds, such as amino acids, phenols, lipids and antioxidants, are found as well, but mostly in trace quantities Baker and Baker, , a. All these substances often impart a particular taste and odour that may be essential for maintaining certain pollinator groups Southwick, In many cases it has been interpreted that pollinators determine nectar components and, thus, the nectar sugar ratios together with flower and inflorescence morphology may be good predictors of the pollinators cf.
Baker and Baker, For instance, hummingbird- and hawk-moth-pollinated flowers tend to produce sucrose-dominant nectar, whereas bee-pollinated flowers tend to produce nectars with a predominance of hexose Baker and Baker, a , b. In addition, experimental studies on sugar preferences of hummingbirds have demonstrated that they preferred sucrose solutions instead of equivalent monosaccharide ones e.
However, in other instances nectar composition may be a conservative character due to phylogenetic constraints cf. Nectar is secreted with particular rhythms, throughout the lifespan of a flower, which allow the nectar production dynamics of a species to be determined. Knowledge of nectar production dynamics is fundamental to the understanding of the plant—animal relationship; aspects such as the plant's strategy of offering nectar, the activity patterns, frequency and diversity of pollinators of a plant species, the rates of nectar consumption by animals, among others, could not be understood without it.
Nectar production may show diverse patterns according to the different guilds of pollinators that visit the flowers e. Feinsinger, ; Cruden et al. For instance, hawk-moth-pollinated flowers produce abundant nectar with low concentration values and bee-pollinated flowers secrete compartively less nectar with higher concentrations, whereas hummingbird-pollinated flowers show intermediate values e. At the same time, the effect of nectar removal by floral visitors may have a pronounced effect on the total amount secreted by a flower. Although in some species removal does not modify nectar production e.
Galetto and Bernardello, , ; Galetto et al. Pyke, ; Galetto and Bernardello, ; Castellanos et al. Galetto and Bernardello, ; Bernardello et al. Predictions for these patterns are not straightforward because they may be related to pollinators, environmental factors, plant resource allocation, or other factors. Six sympatrically occurring Ipomoea species that have differences in the pollinator guilds, floral colours and breeding systems were chosen to examine their floral nectaries, nectar components and nectar production dynamics to evaluate if there are correlations among these features and to consider the results in the context of plant—pollinator interactions.
Its members have trumpet-shaped flowers of different colours—mainly white, purple, blue, pink, red Cronquist, These are visited by a diverse array of animals, including bees, hawk moths, beetles, butterflies, long-tongued flies, hummingbirds and bats e.
These visitors look for the floral nectar secreted by a discoidal nectary surrounding the ovary base Fahn, ; Cronquist, Only five taxa have been examined for their floral nectar composition Keeler, , ; Stucky and Beckmann, ; Freeman et al. The present work was undertaken to study and compare the floral nectaries and nectar features in six Argentinian Ipomoea species addressing the following questions: We expected to find differences in nectar sugar composition and production dynamics among the species as they are visited by different pollinator guilds see above.
The species studied included: Quamoclit with long, white, hawk-moth-pollinated flowers McDonald, , I. Quamoclit with medium-sized, red, allegedly hummingbird-pollinated flowers cf. Wilson, ; Austin, and I. Quamoclit with violet-pink flowers, I. Eriospermum with pink flowers, I.
Ipomoea with blue flowers and I. Ipomoea with pink, white, or purple flowers, all bee-pollinated Real, ; Maimoni-Rodella et al. Ipomoea rubriflora and I. Regarding their breeding system, some species are self-compatible SC , such as I. The source of the populations studied for each analysis is given in Table 1. In each population three to five individuals were sampled. Species and study sites for Ipomoea populations from Argentina, Prov.
In each population studied, flower visitors were recorded on individual plants at the middle of the lifetime of the flower, for 15 min on three different days. Photomicrographs were taken with Kodak T-Max film, ASA, with an Axiophot-photomicrographic system equipped with automatic exposure. Nectary tissue volume was calculated with the non-circular section toroids' formula: This parameter was estimated with reference to the weight of the drawings of the nectary in longitudinal section the two stained areas at the ovary base.
The drawings were made on a homogeneous paper using a camera lucida fitted on a stereomicroscope.
Ovaries for observation under a scanning electron microscope SEM were dehydrated in an acetone series and dried using CO 2 in a critical-point dryer Balzers, Switzerland. Dried samples were mounted and then gold-coated to a thickness of 25 nm Balzers. In the field, nectar drops for each sample were placed in 1 mL vials and quickly frozen.
Sugar concentration and nectar volume were measured in the field with an Atago pocket refractometer and graduated capillary glass tubes, respectively. Tests following Baker and Baker for amino acids, lipids, phenols, alkaloids and reducing acids were made on nectar spots on chromatography paper.
Sugars were identified via gas chromatography.
Nectar was lyophilized and silylated according to Sweeley et al. Nitrogen was the carrier gas and the following temperature programme was used: Chromatographic sugar analyses were run at least twice for each sample. F, were calculated as per Baker and Baker b. Floral longevity was determined in ten bagged flowers by following the flowers' development until the corollas began to wilt. Randomly chosen flowers in the bud stage were bagged using paper bags to prevent pollinator visits and were tagged for identification.
Nectar production was determined by using flower sets of seven to 20 flowers each according to flower availability. Flowers of a set were assigned from different individuals one to four per each plant according to the availability of plants. The sampling schedule took into account the lifetime of the flower of each species, with either four or five flower sets Table 4. Data were taken once for each set, allowing the nectar to accumulate until it was measured. Net nectar production rate NPR per hour was calculated as: Data on the diagonal first measurements of each set underlined correspond to the nectar production dynamics of each species.
The total amount of sugar per flower was calculated for each set using set 4 or 5 as control, according to the species. When statistically significant differences were found, lower-case letters as superscript indicate a posteriori test results. To evaluate the effect of removal on total sugar amount, nectar was removed and measured from the same flower repeatedly during the entire active secretion period.
Nectar was extracted with capillary glass tubes without removing the flowers from the plant, taking extreme care to avoid damage to the nectaries. Sets of seven to 20 flowers were subjected to a different number of removals according to the secretion period of the species. According to the flower lifetime of the species, four or five flower sets were assigned see Table 4 ; for the first measurement, nectar was allowed to gather for approx.
The general scheme was to allow nectar to accumulate for a determined period approx. The total amount of sugar per flower was calculated as the product of nectar volume and sugar concentration per unit volume, e. All distributions were tested for randomness of nominal data Runs test , homogeneity of variances Levene test , and departures from normality Kolmogorov—Smirnov for goodness-of-fit test.
The effects of nectar removal on the total amount of sugar produced by each set of flowers were compared with one-way analysis of variance ANOVA and with the Bonferroni's post hoc test for multiple comparisons among pairs of means, to evaluate the consequences of pollinator visits to each species. Regression analyses were done using species means to estimate if flower traits are explained by the increase of flower size.
The relationship between pollination guilds and nectar traits was assessed by qualitative comparisons because of the low number of hummingbird and hawk-moth species. Hymenopterans were regular visitors of I. The introduced European bee Apis mellifera was occasionally observed on the study species, but most visits corresponded to native bees from the families Apidae Bombus opifex , B.
In the populations of I. The book can be useful to the pollination ecoogist, as well, covering also the relationship between nectar and pollinator. A special value of the book is that it gives useful hints for the practice, too.
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Set up a giveaway. There's a problem loading this menu right now. Get fast, free shipping with Amazon Prime. Your recently viewed items and featured recommendations. View or edit your browsing history. Get to Know Us. English Choose a language for shopping. Amazon Music Stream millions of songs. He is currently employed as researcher at the Department of Environmental Sciences of the University of Siena, where he carries out studies concerning the reproductive biology of angiosperms.
In recent years his main research interest has been nectar and nectary biology. Ettore Pacini graduated in botany in at the University of Siena, where he is still engaged as full professor of Botany. His main research interest has been higher plant reproduction, first from a cytological point of view and also from an ecological point of view during the last two decades.
Recently he became a member of the prestigious Accademia dei Lincei, the first Scientific Academy, founded in View other products from the same publisher. Promote your book on NHBS. Searching and Browsing for Books.
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