, Volume 108, Issue 1, pp 11-13

Colour receptors in the bee eye — Morphology and spectral sensitivity

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Summary

  1. Colour coding in the retina of the honey bee,Apis mellifera, is examined by single unit recording and intracellular marking with the fluorescence dye Procion yellow.

  2. The three receptor types (UV, blue, green receptors) are dominated by three rhodopsin — like pigments with absorbance maxima at 350 nm, 440 nm and 540 nm. This is in general agreement with the first discription of the bee's colour receptors by Autrum and v. Zwehl, 1964.

  3. The UV-receptors were found to be those cells which form the long visual fibres. These penetrate the lamina with differing patterns of short arborisations and spines and project to the 1. or more often to the 2. medullary layer.

  4. Most green receptors we have marked from the deep lamina axons which reach the internal (most proximal) lamina layer and end in several branches. The shallow lamina fibres come from blue or from green receptors.

  5. The majority of cells have secondary sensitivities at wavelength regions where the other receptor types absorb maximally. We show with spectral adaptation experiments that this linkage is caused by a positive electrical coupling. We give arguments which exclude the artificial nature of the electrical coupling.

  6. There is also evidence for negative electrical coupling between different colour receptors. We have recorded from several UV-receptors, which responded with a hyperpolarising potential to long wavelength stimulation. The narrower spectral sensitivity functions when compared with Dartnall resonance functions found in a smaller number of receptors are interpreted to reflect, too, negative electrical interactions between different colour receptors.

  7. We propose a model of electrical interactions of densely packed colour receptors which postulates negative electrical coupling occurring within the retina and positive electrical coupling through the lamina cartridge. Further-more, we discuss our results on the basis of colour integration mechanisms within the lamina.

Supported by a grant from the Deutsche Forschungsgemeinschaft (Az. Me 365/4)