Asymmetric taste discrimination in the honeybee depends on taste similarity and hedonic value
Martin Giurfa, Maria Gabriela de Brito Sanchez , Marie Guiraud , Martin Giurfa
Late; Research Center on Animal Cognition, Center for Integrative Biology, CNRS, University of Toulouse, Toulouse, France ; Research Center on Animal Cognition, Center for Integrative Biology, CNRS, University of Toulouse, Toulouse, France ; Research Center on Animal Cognition, Center for Integrative Biology, CNRS, University of Toulouse, Toulouse, France
In the honeybee, the sense of taste has remained largely unexplored. To fill this void, we established a conditioning protocol in which tastants are no longer reinforcements. Tastants are delivered to the antennae and paired with a mild electric shock. The conditioned sting extension to punished tastants was recorded. In the case of sweeteners, we found that discrimination between a less preferred sweetener and a preferred sweetener was asymmetric. Discrimination was only possible if the former was punished and the latter not; the opposite was impossible. We proposed that when hedonic differences between sweeteners were accentuated by making the less preferred stimulus even more negative via its association with shock, discrimination was possible. If, on the contrary sweetener differences were blurred by pairing the preferred sweetener with shock, discrimination became impossible. Here we show that asymmetric discrimination depends on the perceptual similarity between tastants. We trained bees with mixtures of 1M sucrose and quinine or salicin at the mM range. These compounds inhibit to different extents sucrose receptors, thus yielding a ‘less sweet’ sensation compared to pure sucrose. Bees showed asymmetric discrimination between distilled water and mixtures of sucrose + quinine or sucrose + salicin: when water was punished, bees learned the discrimination, but if the mixture was punished, they could not, a result that contrasts with their perfect and symmetric discrimination of distilled water vs. pure 1M sucrose solution. Asymmetric discrimination was also found between 0.3 M and 1M sucrose. We thus conclude that above a certain discrimination threshold, stimuli are perceived as very different and discrimination is symmetric; yet, when this difference is reduced and stimulus difference is below threshold, tastant similarity engages asymmetric discrimination based on hedonic principles.