Using the Hard, Randy, and Rittler Test to Evaluate Color Vision in Capuchins (Cebus libidinosus)

Uniform trichromacy in Alouatta caraya and Alouatta seniculus: behavioural and genetic colour vision evaluation

Primate colour vision depends on a matrix of photoreceptors, a neuronal post receptoral structure and a combination of genes that culminate in different sensitivity through the visual spectrum. Along with a common cone opsin gene for short wavelengths (sws1), Neotropical primates (Platyrrhini) have only one cone opsin gene for medium-long wavelengths (mws/lws) per X chromosome while Paleotropical primates (Catarrhini), including humans, have two active genes. Therefore, while female platyrrhines may be trichromats, males are always dichromats. The genus Alouatta is inferred to be an exception to this rule, as electrophysiological, behavioural and molecular analyses indicated a potential for male trichromacy in this genus. However, it is very important to ascertain by a combination of genetic and behavioural analyses whether this potential translates in terms of colour discrimination capability. We evaluated two howler monkeys (Alouatta spp.), one male A. caraya and one female A. seniculus, using a combination of genetic analysis of the opsin gene sequences and a behavioral colour discrimination test not previously used in this genus. Both individuals completed the behavioural test with performances typical of trichromatic colour vision and the genetic analysis of the sws1, mws, and lws opsin genes revealed three different opsin sequences in both subjects. These results are consistent with uniform trichromacy in both male and female, with presumed spectral sensitivity peaks similar to Catarrhini, at ~ 430 nm, 532 nm, and 563 nm for S-, M- and L-cones, respectively.

Behavioral and genetic color vision evaluation of an albino male capuchin monkey (Sapajus apella)

Albinism is a rare phenotype that affects the pigmentation in eyes, hair, and skin. The effects of albinism in color vision are still unclear. Our study aimed to evaluate the color vision phenotype and genotype of an albino capuchin monkey. An adult albino male capuchin monkey (Sapajus apella) had the L and M opsin gene analyzed, and was trained in a behavioral task of color discrimination. Color discrimination thresholds were determined along 20 chromatic axes around the background chromaticity. A color discrimination ellipse was drawn by interpolation among these thresholds. The albino monkey's behavioral color discrimination ellipse showed poor discrimination along the red-green axis indicating a deutan phenotype. Genetic analysis revealed only the presence of the L gene in the albino monkey. This result did not differ from that obtained with ten previously tested non-albino monkeys. Behavioral and molecular analyses agreed that the albino capuchin monkey had color vision similar to that of non-albino dichromat monkeys, suggesting no influence of albinism on color discrimination.

Morphological study of the eye and adnexa in capuchin monkeys (Sapajus sp.)

The objective of this study was to describe the anatomic and histologic features of the Sapajus sp. eye, comparing similarities and differences of humans and other species of non-human primates for biomedical research purposes. Computed tomography (CT) of adnexa, eye and orbit live animal, as well as formolized pieces of the same structures of Sapajus sp. for anatomical and histological study were also performed. The anatomical description of the eye and adnexa was performed using the techniques of topographic dissection and exenteration. Histological fragments were fixated in buffered formalin 10%, processed by the routine paraffin inclusion technique, stained with hematoxylin-eosin and special stains. CT scan evaluation showed no differences between the live animal and the formolized head on identification of visual apparatus structures. Anatomic and histologic evaluation revealed rounded orbit, absence of the supraorbital foramen and frontal notch, little exposure of the sclera, with slight pigmentation of the exposed area and marked pigmentation at the sclerocorneal junction. Masson's Trichrome revealed the Meibomian glands, the corneal epithelium and Bowman's membrane; in the choroid, melanocytes and Bruch's membrane were observed; and in the retina, cones and rods as well as, optic nerve, the lamina cribrosa of the nerve fibers bundles. Toluidine blue highlighted the membranes: Bowman, Descemet and the endothelium; in the choroid: melanocytes; and in the retina: nuclear layers and retinal pigment epithelium. In view of the observed results Sapajus sp. is an important experimental model for research in the ophthalmology field, which has been shown due to the high similarity of its anatomical and histological structures with the human species.

Polymorphic color vision in captive Uta Hick's cuxiús, or bearded sakis (Chiropotes utahickae)

The pitheciines (Chiropotes, Pithecia, and Cacajao) are frugivorous Neotropical primates that specialize on the predation of seeds from unripe fruits, usually cryptic against the foliage. However, little is known about the color vision distribution within this taxon, and even less about the abilities shared by these animals regarding discrimination of chromatic targets. The aim of this study was to evaluate the color vision perception of captive Uta Hick's cuxiús, or bearded sakis (Chiropotes utahickae) through a behavioral paradigm of color visual discrimination, as well as to estimate, by genetic studies, the number and kinds of medium to long wavelength cone photopigment (opsins) encoded by this species. Among 12 cuxiús (7 males and 5 females) studied only 1 female was diagnosed as a trichromat. Results from genotyping were in line with our behavioral data and showed that cuxiús carried one (dichromat) or two (trichromat) medium to long wavelength pigments alleles, demonstrating a color vision polymorphism in C. utahickae similar to the majority of Neotropical Primates.