Abstract
Flower colour is mainly due to the presence and type of pigments. Pollinator preferences impose selection on flower colour that ultimately acts on flower pigments. Knowing how pollinators perceive flowers with different pigments becomes crucial for a comprehensive understanding of plant-pollinator communication and flower colour evolution. Based on colour space models, we studied whether main groups of pollinators, specifically hymenopterans, dipterans, lepidopterans and birds, differentially perceive flower colours generated by major pigment groups. We obtain reflectance data and conspicuousness to pollinators of flowers containing one of the pigment groups more frequent in flowers: chlorophylls, carotenoids and flavonoids. Flavonoids were subsequently classified in UV-absorbing flavonoids, aurones-chalcones and the anthocyanins cyanidin, pelargonidin, delphinidin, and malvidin derivatives. We found that flower colour loci of chlorophylls, carotenoids, UV-absorbing flavonoids, aurones-chalcones, and anthocyanins occupied different regions of the colour space models of these pollinators. The four groups of anthocyanins produced a unique cluster of colour loci. Interestingly, differences in colour conspicuousness among the pigment groups were almost similar in the bee, fly, butterfly, and bird visual space models. Aurones-chalcones showed the highest chromatic contrast values, carotenoids displayed intermediate values, and chlorophylls, UV-absorbing flavonoids and anthocyanins presented the lowest values. In the visual model of bees, flowers with UV-absorbing flavonoids (i.e., white flowers) generated the highest achromatic contrasts. Ours findings suggest that in spite of the almost omnipresence of floral anthocyanins in angiosperms, carotenoids and aurones-chalcones generates higher colour conspicuousness for main functional groups of pollinators.
Highlights
The colours of flowers, usually those of petals, mainly act as a signal to attract pollinators by making flowers highly conspicuous against the vegetative background
The vast range of flower colours relies on four major pigment classes: chlorophylls, carotenoids, flavonoids, and betalains (Lee, 2007; Narbona et al, 2021)
The details of biochemical information of flowers containing flavonoids are much more comprehensive than those for the chlorophylls and carotenoids (e.g., Harborne et al, 1975; Harborne and Williams, 2000; Andersen and Markham, 2006); for this reason we only considered pigment subcategories in flavonoids
Summary
The colours of flowers, usually those of petals, mainly act as a signal to attract pollinators by making flowers highly conspicuous against the vegetative background. Each pigment class has a distinctive chemical structure, which affects the specific wavelengths it absorbs and thereby the colour it generates (Grotewold, 2006; Glover, 2007; Tanaka et al, 2008). Chlorophylls absorb in the blue and red regions of the spectrum, generating green colourations for humans; carotenoids mainly absorb in the blue region, giving rise to yellow-orange colourations; and betalains absorb in either the blue or green regions, generating yellow or pink colourations, respectively (Grotewold, 2006; Narbona et al, 2021). Anthocyanins are the flavonoids that generate the most varied colouration to flowers; they absorb in different parts of the green region of the spectrum and produce shades of bluepink-orange-red floral colours (Grotewold, 2006). Each of the major classes of pigments and subcategories contains hundreds or thousands of different compounds that vary in the configuration of the core molecular structure (Davies, 2009), which generally affect the absorption of light and thereby the resulting colour (i.e., hue)
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