Does Fine Color Discrimination Learning in Free-Flying Honeybees Change Mushroom-Body Calyx Neuroarchitecture?

PLoS One. 2016 Oct 26;11(10):e0164386. doi: 10.1371/journal.pone.0164386. eCollection 2016.

Abstract

Honeybees learn color information of rewarding flowers and recall these memories in future decisions. For fine color discrimination, bees require differential conditioning with a concurrent presentation of target and distractor stimuli to form a long-term memory. Here we investigated whether the long-term storage of color information shapes the neural network of microglomeruli in the mushroom body calyces and if this depends on the type of conditioning. Free-flying honeybees were individually trained to a pair of perceptually similar colors in either absolute conditioning towards one of the colors or in differential conditioning with both colors. Subsequently, bees of either conditioning groups were tested in non-rewarded discrimination tests with the two colors. Only bees trained with differential conditioning preferred the previously learned color, whereas bees of the absolute conditioning group, and a stimuli-naïve group, chose randomly among color stimuli. All bees were then kept individually for three days in the dark to allow for complete long-term memory formation. Whole-mount immunostaining was subsequently used to quantify variation of microglomeruli number and density in the mushroom-body lip and collar. We found no significant differences among groups in neuropil volumes and total microglomeruli numbers, but learning performance was negatively correlated with microglomeruli density in the absolute conditioning group. Based on these findings we aim to promote future research approaches combining behaviorally relevant color learning tests in honeybees under free-flight conditions with neuroimaging analysis; we also discuss possible limitations of this approach.

MeSH terms

  • Animals
  • Bees / physiology*
  • Brain / anatomy & histology
  • Brain / metabolism
  • Choice Behavior / physiology
  • Color*
  • Discrimination Learning / physiology*
  • Microscopy, Confocal
  • Mushroom Bodies / anatomy & histology
  • Mushroom Bodies / chemistry
  • Mushroom Bodies / metabolism*
  • Neuropil / physiology
  • Photic Stimulation

Grants and funding

FMJS was supported by a grant of the German Excellence Initiative to the Graduate School of Life Sciences, University of Würzburg. This work was further supported by a PhD research scholarship offered by the Free State of Bavaria (Elitenetzwerk Bayern) to FMJS, and an Australian Research Council grant DP0987989 to AGD, JS and WR. This publication was funded by the German Research Foundation and the University of Würzburg in the funding program Open Access Publishing. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.