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Journal of Experimental Biology, Vol 203, Issue 13 1963-1986, Copyright © 2000 by Company of Biologists
JOURNAL ARTICLES |
P Sumner and JD Mollon
Department of Experimental Psychology, University of Cambridge, UK. gphs100@cam.ac.uk
The colour vision of many primates is trichromatic, whereas that of all other mammals is thought to be dichromatic or monochromatic. Moreover, the triplets of cone pigments in different catarrhines (Old World apes and monkeys) are strikingly similar in their spectral positions. We ask whether the selective advantage of trichromacy lies in an enhanced ability to find edible leaves or fruit. Further, we ask whether any factor in these two search tasks has constrained the particular set of cone spectral sensitivities observed in all catarrhines. We measured the spectral properties of the natural environments of six primate species in Uganda: Pan troglodytes, Cercopithecus mitis, Cercopithecus ascanius, Lophocebus albigena, Colobus guereza and Colobus badius. We concentrated on the fruit and leaves in their diets and the leaves of the trees that make up the background against which these diet items must be found. We plotted these measured stimuli in colour spaces appropriate for each primate species, and found that both frugivory and folivory are facilitated by the extra dimension of colour vision found in catarrhines but lacking in most other mammals. Furthermore, by treating the task of searching for food as a signal-detection task, we show that, of all possible combinations of cone sensitivities, the spectral positions of the actual primate pigments are optimal for finding fruit or young leaves against the background of mature leaves. This is because the variance of the chromaticities of the mature leaves is minimised in one channel of the primate's colour vision, so allowing anything that is not a mature leaf to stand out.
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A. G. Dyer Ocular filtering of ultraviolet radiation and the spectral spacing of photoreceptors benefit Von Kries colour constancy J. Exp. Biol., March 9, 2002; 204(14): 2391 - 2399. [Abstract] [Full Text] [PDF]
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P Sumner and J. Mollon Chromaticity as a signal of ripeness in fruits taken by primates J. Exp. Biol., January 7, 2000; 203(13): 1987 - 2000. [Abstract] [PDF]
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