Bee Colour Space Research Articles

Floral Color Diversity: How Are Signals Shaped by Elevational Gradient on the Tropical-Subtropical Mountainous Island of Taiwan?

Pollinators with different vision are a key driver of flower coloration. Islands provide important insights into evolutionary processes, and previous work suggests islands may have restricted flower colors. Due to both species richness with high endemism in tropical–subtropical environments, and potentially changing pollinator distributions with altitude, we evaluated flower color diversity across the mountainous island of Taiwan in a comparative framework to understand the cause of color diversity. We sampled flower color signaling on the tropical–subtropical island of Taiwan considering altitudes from sea level to 3300 m to inform how over-dispersion, random processes or clustering may influence flower signaling. We employed a model of bee color space to plot loci from 727 species to enable direct comparisons to data sets from continental studies representing Northern and Southern Hemispheres, and also a continental mountain region. We observed that flower color diversity was similar to flowers that exist in mainland continental studies, and also showed evidence that flowers predominantly had evolved color signals that closely matched bee color preferences. At high altitudes floras tend to be phylogenetically clustered rather than over-dispersed, and their floral colors exhibited weak phylogenetic signal which is consistent with character displacement that facilitated the co-existence of related species. Overall flower color signaling on a tropical–subtropical island is mainly influenced by color preferences of key bee pollinators, a pattern consistent with continental studies.

Innate colour preferences of the Australian native stingless bee Tetragonula carbonaria Sm.

Innate preferences promote the capacity of pollinators to find flowers. Honeybees and bumblebees have strong preferences for 'blue' stimuli, and flowers of this colour typically present higher nectar rewards. Interestingly, flowers from multiple different locations around the world independently have the same distribution in bee colour space. Currently, however, there is a paucity of data on the innate colour preferences of stingless bees that are often implicated as being key pollinators in many parts of the world. In Australia, the endemic stingless bee Tetragonula carbonaria is widely distributed and known to be an efficient pollinator of both native plants and agricultural crops. In controlled laboratory conditions, we tested the innate colour responses of naïve bees using standard broadband reflectance stimuli representative of common flower colours. Colorimetric analyses considering hymenopteran vision and a hexagon colour space revealed a difference between test colonies, and a significant effect of green contrast and an interaction effect of green contrast with spectral purity on bee choices. We also observed colour preferences for stimuli from the blue and blue-green categorical regions of colour space. Our results are discussed in relation to the similar distribution of flower colours observed from bee pollination around the world.

Correction to ‘Colour learning when foraging for nectar and pollen: bees learn two colours at once’

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Muth Felicity, Papaj Daniel R. and Leonard Anne S. 2015Correction to ‘Colour learning when foraging for nectar and pollen: bees learn two colours at once’Biol. Lett.112015084120150841http://doi.org/10.1098/rsbl.2015.0841SectionYou have accessCorrectionCorrection to ‘Colour learning when foraging for nectar and pollen: bees learn two colours at once’ Felicity Muth Felicity Muth Google Scholar Find this author on PubMed Search for more papers by this author , Daniel R. Papaj Daniel R. Papaj Google Scholar Find this author on PubMed Search for more papers by this author and Anne S. Leonard Anne S. Leonard Google Scholar Find this author on PubMed Search for more papers by this author Felicity Muth Felicity Muth Google Scholar Find this author on PubMed Search for more papers by this author , Daniel R. Papaj Daniel R. Papaj Google Scholar Find this author on PubMed Search for more papers by this author and Anne S. Leonard Anne S. Leonard Google Scholar Find this author on PubMed Search for more papers by this author Published:01 October 2015https://doi.org/10.1098/rsbl.2015.0841This article corrects the followingResearch ArticleColour learning when foraging for nectar and pollen: bees learn two colours at oncehttps://doi.org/10.1098/rsbl.2015.0628 Felicity Muth, Daniel R. Papaj and Anne S. Leonard volume 11issue 9Biology Letters01 September 2015Biol. Lett.10, 20140628. (2015; Published online 30 September 2015) (doi:10.1098/rsbl.2015.0628)The caption for figure 1 incorrectly indicated that there was a bee in the figure. In fact, there is no bee in the figure. The corrected caption is provided below. Figure 1. (a) Training array (left) and test array (right) (view the supplementary video to see nectar and pollen collection behaviour). (b) Flower colours plotted in bee colour space (y, yellow; o, orange; p, purple; b, blue; centre represents the background; relative distances in electronic supplementary material, table S1). (Online version in colour.)Download figureOpen in new tabDownload PowerPoint Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsRelated articlesColour learning when foraging for nectar and pollen: bees learn two colours at once01 September 2015Biology Letters This IssueOctober 2015Volume 11Issue 10 Article InformationDOI:https://doi.org/10.1098/rsbl.2015.0841PubMed:26490420Published by:Royal SocietyOnline ISSN:1744-957XHistory: Published online01/10/2015Published in print31/10/2015 License:© 2015 The Author(s)Published by the Royal Society. All rights reserved. Citations and impact Subjectsbehaviourcognition Large datasets are available through Biology Letters' partnership with Dryad

Visual and Olfactory Floral Cues of Campanula (Campanulaceae) and Their Significance for Host Recognition by an Oligolectic Bee Pollinator.

Oligolectic bees collect pollen from a few plants within a genus or family to rear their offspring, and are known to rely on visual and olfactory floral cues to recognize host plants. However, studies investigating whether oligolectic bees recognize distinct host plants by using shared floral cues are scarce. In the present study, we investigated in a comparative approach the visual and olfactory floral cues of six Campanula species, of which only Campanula lactiflora has never been reported as a pollen source of the oligolectic bee Ch. rapunculi. We hypothesized that the flowers of Campanula species visited by Ch. rapunculi share visual (i.e. color) and/or olfactory cues (scents) that give them a host-specific signature. To test this hypothesis, floral color and scent were studied by spectrophotometric and chemical analyses, respectively. Additionally, we performed bioassays within a flight cage to test the innate color preference of Ch. rapunculi. Our results show that Campanula flowers reflect the light predominantly in the UV-blue/blue bee-color space and that Ch. rapunculi displays a strong innate preference for these two colors. Furthermore, we recorded spiroacetals in the floral scent of all Campanula species, but Ca. lactiflora. Spiroacetals, rarely found as floral scent constituents but quite common among Campanula species, were recently shown to play a key function for host-flower recognition by Ch. rapunculi. We conclude that Campanula species share some visual and olfactory floral cues, and that neurological adaptations (i.e. vision and olfaction) of Ch. rapunculi innately drive their foraging flights toward host flowers. The significance of our findings for the evolution of pollen diet breadth in bees is discussed.

Parallel evolution of angiosperm colour signals: common evolutionary pressures linked to hymenopteran vision

Flowering plants in Australia have been geographically isolated for more than 34 million years. In the Northern Hemisphere, previous work has revealed a close fit between the optimal discrimination capabilities of hymenopteran pollinators and the flower colours that have most frequently evolved. We collected spectral data from 111 Australian native flowers and tested signal appearance considering the colour discrimination capabilities of potentially important pollinators. The highest frequency of flower reflectance curves is consistent with data reported for the Northern Hemisphere. The subsequent mapping of Australian flower reflectances into a bee colour space reveals a very similar distribution of flower colour evolution to the Northern Hemisphere. Thus, flowering plants in Australia are likely to have independently evolved spectral signals that maximize colour discrimination by hymenoptera. Moreover, we found that the degree of variability in flower coloration for particular angiosperm species matched the range of reflectance colours that can only be discriminated by bees that have experienced differential conditioning. This observation suggests a requirement for plasticity in the nervous systems of pollinators to allow generalization of flowers of the same species while overcoming the possible presence of non-rewarding flower mimics.

FReD: The Floral Reflectance Database — A Web Portal for Analyses of Flower Colour

BackgroundFlower colour is of great importance in various fields relating to floral biology and pollinator behaviour. However, subjective human judgements of flower colour may be inaccurate and are irrelevant to the ecology and vision of the flower's pollinators. For precise, detailed information about the colours of flowers, a full reflectance spectrum for the flower of interest should be used rather than relying on such human assessments.Methodology/Principal FindingsThe Floral Reflectance Database (FReD) has been developed to make an extensive collection of such data available to researchers. It is freely available at http://www.reflectance.co.uk. The database allows users to download spectral reflectance data for flower species collected from all over the world. These could, for example, be used in modelling interactions between pollinator vision and plant signals, or analyses of flower colours in various habitats. The database contains functions for calculating flower colour loci according to widely-used models of bee colour space, reflectance graphs of the spectra and an option to search for flowers with similar colours in bee colour space.Conclusions/SignificanceThe Floral Reflectance Database is a valuable new tool for researchers interested in the colours of flowers and their association with pollinator colour vision, containing raw spectral reflectance data for a large number of flower species.

Can red flowers be conspicuous to bees?Bombus dahlbomiiand South American temperate forest flowers as a case in point

It has been argued that trichromatic bees with photoreceptor spectral sensitivity peaks in the ultraviolet (UV), blue and green areas of the spectrum are blind to long wavelengths (red to humans). South American temperate forests (SATF) contain a large number of human red-looking flowers that are reported to be visited by the bumblebee Bombus dahlbomii. In the present study, B. dahlbomii's spectral sensitivity was measured through electroretinogram (ERG) recordings. No extended sensitivity to long wavelengths was found in B. dahlbomii. The spectral reflectance curves from eight plant species with red flowers were measured. The color loci occupied by these flowers in the bee color space was evaluated using the receptor noise-limited model. Four of the plant species have pure red flowers with low levels of chromatic contrast but high levels of negative L-receptor contrast. Finally, training experiments were performed in order to assess the role of achromatic cues in the detection and discrimination of red targets by B. dahlbomii. The results of the training experiments suggest that the bumblebee relies on achromatic contrast provided by the L-receptor to detect and discriminate red targets. These findings are discussed in the context of the evolutionary background under which the relationship between SATF species and their flower visitors may have evolved.

Nectar Production Rates of 75 Bumblebee-visited Flower Species in a German Flora (Hymenoptera: Apidae: Bombus terrestris).

(Linneaus 1758) workers near Wurzburg (Bavaria, Germany) were measured between 1999 and 2002. Production rates were calculated for each flower species from the volume and concentration of nectar produced by 30-60 flowers per species over a 3 hour period during which visitation was prevented. The average amount of sugar produced (µg in 24 hours) is given below for each flower species. The spectral reflectance of all flower species were quantified, converted into bee colour space loci [C

Foraging decisions in nectarivores: unexpected interactions between flower constancy and energetic rewards

Foraging decisions are based on a suite of choices that include energetics and physiological constraints. Although travelling farther to harvest a greater net energetic reward is beneficial, many animals opt for a smaller net reward that requires less travel. Recent discoveries of a visual basis for flower constancy in the honeybee, Apis mellifera, led us to examine older reports that colour cues are superceded by energetic considerations. Here we show that when individual bees foraged on pedicellate artificial flowers varying in colour and interfloral distance, their behaviour depended on the colours in the choice test. Colours of similar spectral reflectance (blue versus white), that would be clustered in the bee's visual colour space, elicited more visits to the closest flower when rewards were equal, but individuals travelled a greater distance to harvest a higher energetic reward when reward quality varied. Bees chose the closest flower more often when reward volume decreased while quality remained constant. Yet, even when all flowers were identical (morphology and reward), and only interfloral distance varied, bees did not always visit the closest flower. A dramatic difference was seen when the dimorphism was yellow-blue, colours quite separate in the bee colour space and known to elicit constancy behaviour. Here, bees visited the closest flower only 5% of the time, and varying reward volume did not elicit different behaviour. Animals thus display differential foraging behaviour with respect to environmental cues that must be considered when asking questions about other behavioural parameters.

Floral colour diversity in plant communities, bee colour space and a null model

Evolutionary biologists have long hypothesized that the diversity of flower colours we see is in part a strategy to promote memorization by pollinators, pollinator constancy, and therefore, a directed and efficient pollen transfer between plants. However, this hypothesis has never been tested against a biologically realistic null model, nor were colours assessed in the way pollinators see them. Our intent here is to fill these gaps. Throughout one year, we sampled floral species compositions at five ecologically distinct sites near Berlin, Germany. Bee-subjective colours were quantified for all 168 species. A model of colour vision was used to predict how similar the colours of sympatric and simultaneously blooming flowers were for bees. We then compared flower colour differences in the real habitats with those of random plant communities. We did not find pronounced deviations from chance when we considered common plants. When we examined rare plants, however, we found significant divergence in two of the five plant communities. At one site, similarly coloured species were found to be more frequent than expected, and at the other two locations, flower colours were indistinguishable from a random distribution. These results fit theoretical considerations that rare plants are under stronger selective pressure to secure pollination than common plants. Our study illustrates the power of linking such distinct biological traditions as community ecology and the neuroethology of bee vision.

BEE COLOR VISION IS OPTIMAL FOR CODING FLOWER COLOR, BUT FLOWER COLORS ARE NOT OPTIMAL FOR BEING CODED—WHY?

Model calculations are used to determine an optimal color coding system for identifying flower colors, and to see whether flower colors are well suited for being encoded. It is shown that the trichromatic color vision of bees comprises UV, blue, and green receptors whose wavelength positions are optimal for identifying flower colors. But did flower colors actually drive the evolution of bee color vision? A phylogenetic analysis reveals that UV, blue, and green receptors were probably present in the ancestors of crustaceans and insects 570 million years ago, and thus predate the evolution of flower color by at least 400 million years. In what ways did flower colors adapt to insect color vision? The variability of flower color is subject to constraint. Flowers are clustered in the bee color space (probably because of biochemical constraints), and different plant families differ strongly in their variation of color (which points to phylogenetic constraint). However, flower colors occupy areas of color space that are significantly different from those occupied by common background materials, such as green foliage. Finally, models are developed to test whether the colors of flowers of sympatric and simultaneously blooming species diverge or converge to a higher degree than expected by chance. Such effects are indeed found in some habitats.

WHY RED FLOWERS ARE NOT INVISIBLE TO BEES

A pervasive idea among pollination biologists is that bees cannot see red flowers. This idea has led many workers to assume that red coloration is an adaptation by which flowers exclude bees as visitors. However, recent empirical and theoretical evidence strongly supports the alternative view, that red flowersarevisible to bees. Our purpose is to marshal this evidence from physiology, behavior, and ecology. First, we define the spectral boundary between orange and red, and show that the visual spectrum of all bee species studied to date extends enough into long wavelengths to provide sensitivity to red light. Such sensitivity differs from the ability to discriminate different monochromatic lights, and we argue that bees will be unable to discriminate such lights above about 550 nm. Second, we point out that flowers do not reflect monochromatic lights. Instead many of them, particularly those that appear red, orange, yellow, and white to humans, have reflectance patterns that are essentially step functions. We predict that bees should be able to discriminate such reflectance patterns over a range of 550–650 nm, since reflectance functions with steps at such wavelengths will occupy different loci in bee color space and thus be distinguishable. In this sense, bees should distinguish between green-, yellow-, orange-, and red-reflecting objects, even if these do not reflect in shorter wavelengths (including UV). A behavioral experiment shows that bumblebees can indeed perform this task. Third, we present information on the spectral reflectance of some typical “red” flowers, combined with field observations of bee visitation to such flowers. We end with a preliminary reassessment of the adaptive significance of red flower coloration, using North American “hummingbird” flowers as an example; we also stress some of the pitfalls facing evolutionary biologists who continue to assume that bees are blind to red objects.