Investigations of polymorphic colour vision in new world primates

Primate colour vision in New World primates is intriguingly complex; show a polymorphism where males are obligatory dichromats (i.e. perception similar to colour-blind humans that cannot differentiate red from green) Females can be either dichromats or trichromats (vision similar to normal humans). The role of such polymorphism remains unclear; however, two often tested hypotheses are related to predator detection and the locating of specific food resources. Here we investigated behavioural changes in male and female primates relating to the colour vision phenotypes and niche divergence as an adaptive feature responsible for maintaining colour vision polymorphism. For polymorphic colour vision to be complementary advantageous, primates should be able to perceive the behavioural changes resulting from sensory abilities of conspecifics. Cooperation tests were used with captive primates to investigate the possibility of primates recognising the visual ability of other individuals in the group. A molecular study of medium-long wavelength sensitive opsin alleles in Pitheciidae indicated a greater variation than reported in the literature and such complexity might increase the number of females with trichromatic colour vision. From a geographical analysis of South American primates, we found that primates avoided areas with high predator richness; however, species that possessed more complex colour vision systems were unaffected by predator richness. Thus, colour vision might be related to complementary advantages in having different colour vision systems in the same group (again increasing the probability of trichromats). Alternative methodologies (i.e. Machine Learning and Computer Vision) were employed to investigate the fitness of different phenotypes in detecting camouflaged targets showing that, contrary to from traditional hypothesis of advantages of dichromatic colour vision, trichromatic colour vision models are best suited for breaking through camouflage. A proof of concept to improve the collection of behavioural data and to investigate the role of cooperation for the maintenance of polymorphic colour vision is also presented. In conclusion, colour vision polymorphism in New World primates enhances the visual abilities of primate groups and is maintained by niche sexual diversification