Abstract
Entomophilous plants have evolved colorful floral displays to attract flower visitors to achieve pollination. Although many insects possess innate preferences for certain colors, the underlying proximate and ultimate causes for this behavior are still not well understood. It has been hypothesized that the floral rewards, e.g., sugar content, of plants belonging to a particular color category correlate with the preference of the flower visitors. However, this hypothesis has been tested only for a subset of plant communities worldwide. Bumble bees are the most important pollinators in alpine environments and show a strong innate preference for (bee) “UV-blue” and “blue” colors. We surveyed plants visited by bumble bees in the subalpine and alpine zones (>1,400 m a.s.l.) of the Austrian Alps and measured nectar reward and spectral reflectance of the flowers. We found that the majority of the 105 plant samples visited by bumble bees fall into the color categories “blue” and “blue-green” of a bee-specific color space. Our study shows that color category is only a weak indicator for nectar reward quantity; and due to the high reward variance within and between categories, we do not consider floral color as a reliable signal for bumble bees in the surveyed habitat. Nevertheless, since mean floral reward quantity differs between categories, naïve bumble bees may benefit from visiting flowers that fall into the innately preferred color category during their first foraging flights.
Highlights
Flower color is a major trait by which plants convey information about their identity and location to a potential visitor
We investigated the visual properties and the reward quantity of bumble bee visited flowering plants in an alpine environment
Our study surprisingly showed a negative correlation between the color contrast and nectar reward, which seems to stand in contrast to the observation that bumble bees prefer flowers of high color contrast (Rohde et al, 2013)
Summary
Flower color is a major trait by which plants convey information about their identity and location to a potential visitor. One of the major pollinator groups of angiosperms, possess three distinct photoreceptor types in their compound eyes, which are most sensitive in the ultraviolet (UV), blue and green part of the light spectrum and enable them to use trichromatic color vision. The number of different photoreceptors and their sensitivity maxima are phylogenetically conserved among most bees (Peitsch et al, 1992; Briscoe and Chittka, 2001) and their origin predates that of angiosperms (Chittka, 1996). As other floral traits like scent, shape or size, are used by flower visitors to detect and identify specific plants and to associate reward quantity and quality after a visit with a particular floral display. Pollinators are able to predict the reward probability of a
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