Modulação da aprendizagem visual por aminas biogênicas e sensibilidade espectral da fototaxia positiva em Apis mellifera

Abstract

The honeybee Apis mellifera represents a traditional model for studies of visual perception and learning. Operant appetitive conditioning of free-flying bees has been the main methodology used so far in these studies, but this approach can hardly be combined with invasive protocols for studying underlying neurobiological mechanisms. Therefore, efforts have been made to de-velop new protocols of classical visual conditioning with harnessed bees in the laboratory, but learning performances remain considerably weaker than those obtained in free-flying animals. In a classical conditioning framework, chromatic luminous stimuli are better learned by har-nessed bees in the laboratory than visual stimuli composed of colored images that reflect the environmental light. However, two problems are associated with the use of chromatic luminous stimuli in these studies: 1- differences in perceptual intensity of the stimuli can hardly be cali-brated, impeding conclusions about whether bees learn to discriminate the intensity or the color of the stimuli; 2-bees present a strong positive phototaxis to light, which may influence the per-ceptual salience of these stimuli. The present work aimed to fill these gaps through an integra-tive study that analyzed how some physical, neurobiological and cognitive factors modulate visual learning and phototaxis in bees. We first investigated the ability of bees to use visual in-formation acquired during classical conditioning to discriminate visual stimuli in a new operant context. For this purpose, we performed classical differential conditioning of the proboscis ex-tension reflex, followed by operant orientation tests in a Y-maze, using the same pair of lumi-nous stimuli. In order to avoid the influence of phototaxis in this experiment, we performed a previous calibration of the irradiance of the chromatic-stimuli pair to a point of perceptual isoluminance. Visual discrimination transfer was clearly observed, with pre-trained honeybees significantly orienting their flights towards the former rewarded stimulus. We thus show that visual memories acquired by honeybees are resistant to context changes between conditioning and the retention test. We combined this visual discrimination approach with selective pharma-cological injections to evaluate the effect of dopamine and octopamine in appetitive visual learn-ing. Both octopaminergic and dopaminergic antagonists impaired visual discrimination perfor-mance, suggesting that both these biogenic amines modulate appetitive visual learning in hon-eybees. We also performed a behavioral study to evaluate how light wavelength and the photo-receptors present in the ocelli or the compound eyes influence the positive phototactic responses of bees. By evaluating the trajectories of bees that are guided in the dark by monochromatic lights of different intensities, we observed that distinct wavelengths differently modulate the phototactic response. In addition, different contributions of the ocelli and the compound eyes for this modulation were found. Our study brings an important contribution to the understanding of neurophysiological and cognitive mechanisms underlying positive phototaxis and visual learn-ing in honeybees.