Cone pigment polymorphism in New World monkeys: Are all pigments created equal?

Abstract

Most platyrrhine monkeys have a triallelic M0L opsin gene polymorphism that underlies significant individual variations in color vision. A survey of the frequencies of these polymorphic genes suggests that the three alleles occur with equal frequency among squirrel monkeys (subfamily Cebinae), but are not equally frequent in a number of species from the subfamily Callitrichinae. This departure from equal frequency in the Callitrichids should slightly increase the ratio of dichromats to trichromats in the population and significantly alter the relative representation of the three possible dichromatic and trichromatic phenotypes. A particular feature of the inequality is that it leads to a relative increase in the number of trichromats whose M0L pigments have the largest possible spectral separation. To assess whether these trichromatic phenotypes are equally well equipped to make relevant visual discriminations, psychophysical experiments were run on human observers. A technique involving the functional substitution of photopigments was used to simulate the discrimination between fruits among a background of leaves. The goal of the simulation was to reproduce in the cones of human observers excitations equivalent to those produced in monkey cones as the animals view fruit. Three different viewing conditions were examined involving variations in the relative luminances of fruit and leaves and the spectrum of the illuminant. In all cases, performance was best for simulated trichromacies including M0L pigments with the largest spectral separation. Thus, the inequality of opsin gene frequency in Callitrichid monkeys may reflect adaptive pressures.

Color vision in marmosets and tamarins: behavioral evidence

“…A more recent and complete survey by Rowe and Jacobs [2004] supports this pattern (with 37%, 20%, and 44% reported for the 543, 556, and 562 nm opsins, respectively), as does a new data set reported in this volume by Surridge et al Taken together, these findings suggest that the intermediate opsin (556 nm) may be less advantageous than the other two opsins (543 and 563 nm). By means of frequency-dependent selection, an opposing advantage and disadvantage would maintain the minority allele at a stable frequency [Mollon et al, 1984], ensuring the perpetuation of a color-vision polymorphism in callitrichids.…”

Detection of fruit by theCerrado's marmoset (Callithrix penicillata): modeling color signals for different background scenarios and ambient light intensities

“…Based on information of Table 5, our predictions would be that phenotype advantage would follow both demands for widely spaced and longer M/L pigments in trichromats, with phenotype 543/562 nm enjoying the larger benefit, 543/556 nm being the least profitable phenotype and 556/562 nm presenting an intermediate advantage. In concurrence with that, allele 562 nm would be the most frequent, followed by allele 543 nm and allele 556 nm, just as described for living populations of callitrichids (Rowe and Jacobs, 2004;Surridge et al, 2005).…”

Bare skin, blood and the evolution of primate colour vision

“…Saguinus, Leontopithecus, Callimico, Cebuella and Callithrix) trichromat phenotypes, two of the three possess near optimal sensitivity to oxygen saturation, and the third (approximately 556/562) possesses little or no sensitivity (figure 2b). It is interesting to note in this regard that the M/L cone with maximal sensitivity at 556 nm occurs disproportionately rarely in the population (Rowe & Jacobs 2004), only 19.7%, perhaps because the 556/562 phenotype is insensitive to oxygen saturation variation. Our hypothesis predicts sensitivity to skin colour variation not just for the early visual mechanisms (i.e., cone sensitivities and opponency), but in Figure 2. (a) The curve shows the difference between the absorption spectrum for oxygenated and deoxygenated haemoglobin.…”