For whales and seals the ocean i...( Discovery of a paradoxical colou...)

Discovery of a paradoxical colour-blindness in marine mammals

Most mammals have reasonable colour vision on the basis of two spectral types of cone photoreceptors, the blue cones and green cones. Researchers at the Max Planck Institute for Brain Research in Frankfurt/M., the Alfred Wegener Institute in Bremen, and the University of Lund (Sweden) have now discovered that whales and seals do not possess blue cones (European Journal of Neuroscience, Vol. 13, pp. 1520-1528, April 2001). These marine mammals only have green cones and hence are colour-blind, because colour discrimination is impossible with only one type of cone. In contrast, the terrestrial relatives of whales and seals possess both cone types. The loss of the blue cones in marine mammals appears particularly enigmatic as in clear ocean waters the penetrating light becomes increasingly blue-shifted with depth.

Man and many other primates have rather acute colour vision. Their so-called 'trichromatic' colour vision is based on the presence of three types of cone photoreceptors with different spectral sensitivities in the retina: blue, green and red cones. Most other mammals have reasonable but less refined colour vision, as they possess only two spectral types of cone, blue cones and green cones (blue cones and red cones in some species). Such dichromatic colour vision is the basic mammalian pattern. However, a German-Swedish group of researchers now discovered that two major groups of marine mammals, the whales and seals, do not possess any blue cones; they only have green cones and hence are colour-blind. With just one spectral type of cone (cone monochromacy) colour discrimination is not possible. Furthermore, without blue cones the detection of contrast and brightness (i. e. non-chromatic cues) is very poor in the blue part of the spectrum. Given the fact that in clear oceanic waters the penetrating light becomes increasingly blue-shifted with depth, the loss of blue co
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Contact: Dr. Leo Peichl
peichl@mpih-frankfurt.mpg.de
49-69-96769-348
Max-Planck-Gesellschaft
19-Apr-2001