Within-species variations in visual capacity among squirrel monkeys (Saimiri sciureus): color vision.

Color vision was studied in 27 squirrel monkeys (Saimiri sciureus) of Peruvian origin (Roman Arch variety). Tests of wavelength discrimination and Rayleigh matching as well as a search for a spectral neutral point were carried out in a behavioral paradigm involving a three-alternative, forced-choice discrimination. Significant individual variations in color vision were found in this species. Some squirrel monkeys have trichromatic color vision, others are dichromats. Within each of these catagories there appear to be three subtypes. Each of these color vision phenotypes can be interpreted as reflecting the presence of a different combination of the types of cone photopigments known to characterize this species. There is a striking gender difference in squirrel monkey color vision; whereas both trichromatic and dichromatic female monkeys were found, all of the males tested were dichromats.