Plants produce flowers with complex visual and olfactory signals, but we know relatively little about the way that signals such as floral scents have evolved. One important factor that may direct the evolution of floral signals is a pollinator's ability to learn. When animals learn to associate two similar signals with different outcomes, biases in their responses to new signals can be formed. Here, we investigated whether or not pollinators develop learned biases towards floral scents that depend on nectar reward quality by training restrained honeybees to learn to associate two similar odour signals with different outcomes using a classical conditioning assay. Honeybees developed learned biases towards odours as a result of differential conditioning, and the extent to which an olfactory bias could be produced depended upon the difference in the quality of the nectar rewards experienced during conditioning. Our results suggest that differences in reward quality offered by flowers influence odour recognition by pollinators, which in turn could influence the evolution of floral scents in natural populations of co-flowering plants.

Complex odours often possess perceptual qualities that are distinct from their components. Previous studies in humans, rodents, and insects indicate that the perception of complex odour blends depends on the concentration of the components and the mixture's complexity. However, we know relatively little about the way that an odour mixture 'gestalt' is produced by the olfactory system. Here, using an assay for olfactory conditioning in the honeybee (Apis mellifera), we examine the role of γ-aminobutyric acid receptor A (GABA(A) )-ergic inhibition within the olfactory primary relay, the antennal lobe, in the formation of a unique odour percept for complex odours. We found that honeybees perceive odour mixtures as configural stimuli when the mixtures were of low concentration and when they were composed of more than two odorants. When GABA(A) receptors were disrupted using the antagonist, picrotoxin, injected directly into the antennal lobe, we observed that bees no longer perceived the mixture as a configural stimulus. Our results imply that synchronization of antennal lobe projection neurons mediated by GABA(A) receptors is the mechanism responsible for the formation of unique olfactory percepts for complex odours.

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