Colour vision in butterflies - I. Single colour experiments

Abstract

1.The retinula cells ofVanessa are similar in physiological properties, including spectral sensitivityS(λ) and negative electrical coupling, to those already described inPapilio, except that red-sensitive cells have not been found in either retina or lamina. 2. In the dark-adapted eye, with a stimulus of one colour, lamina ganglion cells yield only hyperpolarizations. 3. Some lamina ganglion cells (LMC's) have a broad flatS(λ) with angular sensitivity showing that they receive summed input from only one ommatidium. Others have narrowS(λ) and narrow field suggesting that primary receptors from single ommatidia interact on or before reaching them. Narrow peaks are near 500 or 550 nm, but not spread through the spectrum, suggesting colour specific behaviour rather than colour vision. 4. Vanessa itea, V. kershawi, Precis villida andHeteronympha merope all have optomotorS(λ) similar to the curves for green-sensitive photoreceptors, with broad peak between 500 and 550 nm. 5. Optomotor responses of butterflies fall off rapidly around 0.1 cd·m−2, whereas insects with superposition eyes are 100 times more sensitive. Calibrations suggest that the butterfly optomotor threshold is well above the photon flux that yields abundant bumps in the retinula cells. 6. There is difficulty in reconciling theS(λ) of the optomotor response with theS(λ) of any of the individual LMC's. 7. The physiological properties of receptors, LMC's and deep optic lobe units are brought together in a discussion of insect colour vision.