Although trichromatic color vision has been extensively studied as it grants significant advantages for Old World primates, it is unknown which selective pressures were behind trait’s evolution. The leading hypothesis would be that colour vision arose as a foraging adaptation because it allowed individuals to spot food more efficiently. To test this, we exposed three chimpanzees (Pan troglodytes), five gorillas (Gorilla gorilla) and three mandrills (Mandrillus sphinx) to colour cardboard plates to assess if colours related to diet were the most preferred. Experimental setting was divided in two phases. During the first one, animals were provided with colour cardboard plates of only one colour per data collection session. The order of colour presentation was randomly determined: white, black, yellow, green and red. In phase two, primates were simultaneously provided with cardboard plates of all colours. Behavioural interactions with plates were measured using a one-zero group focal sampling (10 s sampling intervals and 20 m observation periods). Results showed that when animals were exposed to only one colour at a time, they exhibited different colour preferences depending on the species considered. Chimpanzees preferred red and yellow, the colours linked to fruits, while gorillas selected red and white. Mandrills exhibited fewer differences between colours preference, being red the most selected. Furthermore, when all colours were simultaneously provided, individuals chose colours related to diet over black and white. Although there were clear individual differences, our results support that trichromatic color vision is an advantage in detecting and selecting red items. In the wild, it could be important in the detection of reddish fruits and leaves.
Food hardness and stone tool weight in wild primate nut-cracking
