Abstract
X-linked photopigment polymorphisms produce several color vision phenotypes in most New World monkeys. In callitrichids, the alleles underlying these phenotypic differences are present at unequal frequencies suggesting selective pressures beyond heterozygous-advantage. We investigated this hypothesis with functional substitution, the use of a computer monitor to synthesize colors as they would appear to humans with monkey visual pigments (Vis. Neurosci. 21:217–222, 2004). The stimuli were derived from measurements of fruit and foliage. For some conditions, discrimination performance depended on the spectral positioning of the substituted M and L pigment pair. The M/L pigment pair with absorption peaks separated by only 6 nm performed relatively poorly. In more recent experiments we systematically varied two parameters, luminance and stimulus duration. Under some conditions, discriminability did not depend upon which phenotype was simulated. Conditions which favored phenotypes with the larger pigment peak separations tended to be those featuring higher luminance and shorter presentation times. These results indicate that an understanding of the selection pressures affecting photopigment allele frequencies will require careful study of the conditions that provide particular alleles with an advantage. Monkeys may compensate for genetic disadvantages by preferentially performing activities under conditions in which such disadvantages are minimized.