Abstract
Old World primates have trichromatic vision because they have three types of cone photoreceptors, each of which is maximally sensitive to long (L)-, middle (M)- and short (S)- wavelengths of light. Although a proportion of human males (about 8 % of Caucasians, for example) have X-chromosome-linked color-vision abnormalities, no non-human Old World primates had been found to be color-vision defective to date. However, our molecular genetic analysis showed the existence of male protanopes and female heterozygotes among the long-tailed macaques in Pangandaran National Park, Indonesia (Onishi et al., 1999). The genome of male protanopes contains a single hybrid gene consisting of exons 1 to 4 of the L-photopigment gene and exons 5 and 6 of the M-photopigment gene (L4M5). The absorbance spectrum of L4M5 photopigment was very close to that of M-photopigment. We confirmed the phenotypes of these monkeys by electroretinogram (ERG) flicker photometry (Hanazawa et al., 2001) and by a pattern discrimination task with modified Ishihara pseudo-isochromatic plates (Mikami et al., 2001). The frequency of protanopes in this species was 0.4 %, much lower than in humans. No dichromatic monkeys were found in other macaque species (Onishi et al., 2002). We surveyed long-tailed macaques in Pangandaran National Park, 4 times between 1998 and 2002. This genotype was restricted to 3 neighboring groups among 8 groups in this area. We further surveyed variations of the long- and middle-wavelength-sensitive opsin genes in west and central Jawa, and in southern Thailand. We found another type of hybrid gene in west Jawa and multiple M opsin genes in southern Thailand. In both cases, those genotypes were restricted to each respective area. These results must be helpful to understand the evolution of color vision in primates.
