Abstract
Free-flying honeybees acquire color information differently depending upon whether a target color is learnt in isolation (absolute conditioning), or in relation to a perceptually similar color (differential conditioning). Absolute conditioning allows for rapid learning, but color discrimination is coarse. Differential conditioning requires more learning trials, but enables fine discriminations. Currently it is unknown whether differential conditioning to similar colors in honeybees forms a long-term memory, and the stability of memory in a biologically relevant scenario considering similar or saliently different color stimuli. Individual free-flying honeybees (N = 6) were trained to similar color stimuli separated by 0.06 hexagon units for 60 trials and mean accuracy was 81.7% ± 12.2% s.d. Bees retested on subsequent days showed a reduction in the number of correct choices with increasing time from the initial training, and for four of the bees this reduction was significant from chance expectation considering binomially distributed logistic regression models. In contrast, an independent group of 6 bees trained to saliently different colors (>0.14 hexagon units) did not experience any decay in memory retention with increasing time. This suggests that whilst the bees’ visual system can permit fine discriminations, flowers producing saliently different colors are more easily remembered by foraging bees over several days.
Highlights
Honeybees are effective pollinators of flowering plants, including many species of high economic value [1]
The high value of color as a cue for bees finding profitable flowers is evidenced by the evolution of many flowering species to produce spectral signals that are best discriminated by the visual system of honeybees [9], or other trichromatic bees that share very similar color discrimination characteristics [10,11]
Honeybees from Group 1 trained with differential conditioning to similar color stimuli were able to reliably learn the target color as mean accuracy on the initial day 1 test was 81.7% ± 12.2% s.d
Summary
Honeybees are effective pollinators of flowering plants, including many species of high economic value [1]. Is has been shown that bees have trichromatic vision [18] with best discrimination at about 400 and 500 nm where photoreceptor sensitivities overlap [19], and bees learn saliently different spectral colors within a few trials [20] Such learning fits both with regions of the spectrum for which discrimination is best, and flower cues that tend to be more associated with profitable nectar rewards [21]. In complex natural conditions the color of flowers from competing plant species may not always be saliently different, a significant problem that the visual system of the bee has to deal with is reliably discriminating between colored flowers, especially as mimic flowers try to gain visits by deception without offering rewards [3,22]. The findings present new insights for both the rich plasticity of honeybee memories [27], and how pollinators make decisions using color information in complex environments [28]
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