Fig. 2

Colour vision evaluation. Colour discrimination ellipses estimated from (A) a trichromatic male of black howler monkey (Alouatta caraya), (B) a trichromatic female of red howler monkey (A. seniculus), (C) a dichromatic male capuchin monkey (Sapajus sp.) and (D) a trichromatic female capuchin monkey (Sapajus sp.). The capuchin monkeys were evaluated in previous work from our group [21, 25], were tested using the same apparatus for only one of the background chromaticities, and were included to allow comparison with the Alouatta phenotype. Black circles show the fitted ellipses for the group of chromatic vector thresholds tested at each background chromaticity. Thresholds correspond to vector lengths in u’v’ units of the 1976 CIE chromaticity diagram along each of 20 equally spaced vectors connecting to the background chromaticity. The crosses represent the background chromaticity for each ellipse, and the tested vectors thresholds for the first background (E1, u’ = 0.1977, v’ = 0.4689) are shown with black dots, for the second (E2, u’ = 0.1925, v’ = 0.5092) with black diamonds and for the third (E3, u’ = 0.2044, v’ = 0.4160) with black triangles