Dichromacy in the antelope ground squirrel

Abstract

The antelope ground squirrel ( Ammospermophilus leucurus) appears to have a form of color vision analogous to that of the human protanope or extreme protanomolous trichromat. This conclusion is based on behavior responses of the animals to illuminated colored ports to which they were conditioned. In this experiment the reward for a correct response was a sunflower seed given to the squirrel at a location which was symmetrical to the colored test port and the comparison port from which the test port was being discriminated. In such tests the squirrels were unable to discriminate red or green on the basis of wavelength. They reacted as if they were red-green color blind. In contrast, the color blue was well discriminated from other colors and from white light, and this was seen in positive responses to the blue port as well as in negative responses, i.e. those in which the animal went away from the blue port. Additionally, the squirrels behaved as if they were able to discriminate yellow as a color, although some evidence of a desaturation effect was obtained in the appearance of the yellow. The total evidence suggested that these squirrels possess a yellow-blue mechanism for discriminating hue. In the experiments, accounting was made of luminosity, smell, and other sensory clues which might explain the results. None of these appear to be responsible for the responses although in improperly designed experiments, non-visual clues, probably via the sense of smell, were involved in determining the behavior.