Bee Color Vision Is Optimal for Coding Flower Color, but Flower Colors Are Not Optimal for Being Coded—why?

Abstract

Model calculations are used to detennine 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.

Geographic patterns in fruit colour diversity: do leaves constrain the colour of fleshy fruits?

“…Second, the conspicuousness of fruit colours is not optimised according to avian vision (Schaefer et al 2007). Similarly, floral colours are not optimal for insects to discriminate among flowers of different species (Chittka 1997). In both cases, non-optimality might be explained by physiological, biochemical, or phylogenetic constraints.…”

Optimal mechanisms for finding and selecting mates: how threespine stickleback ( Gasterosteus aculeatus ) should encode male throat colors

“…One of the most studied signal/receiver systems in this regard is the color vision of insect pollinators and the flowers with which they interact (Chittka 1996;Chittka 1997;Chittka and Briscoe 2001 The evolutionary history we are trying to untangle is potentially paralleled not only by insects and flowers. Similar scenarios may be proposed, for instance, for primates and fruit; did trichromacy evolve in primates to aid in detecting and selecting ripened fruit (Hunt et al 1998;Mollon 1989;Osorio and Vorobyev 1996;Regan et al 1998;Smith et al 2003), or did fruit color evolve to attract seed dispersers more effectively?…”

Bird pollination of Canary Island endemic plants

“…For details see Gumbert et al (1999) and Chittka (1997). For bees specifically, we were interested in the question of whether the bird flowers might be cryptic for bees, as an adaptation to exclude them as visitors.…”

“…For bees specifically, we were interested in the question of whether the bird flowers might be cryptic for bees, as an adaptation to exclude them as visitors. For this purpose, colour loci of the stimuli were calculated in the hexagon colour space, where coding is performed by two unspecified colour opponent mechanisms and colour distance is calculated as the Euclidean distance between stimuli loci in colour space (Chittka 1997). We also evaluated green contrast (i.e.…”