Colour preferences in relation to diet in chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla), and mandrills (Mandrillus sphinx)

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.

New insights in Cercopithecinae spermatozoa

Summary Sperm morphometric and morphologic data have been shown to represent useful tools for monitoring fertility, improving assisted reproduction techniques and conservation of genetic material as well as detecting inbreeding of endangered primates. We provide here for the first time sperm morphologic and morphometric data from Cercopithecus neglectus, Cercopithecus cephus, Papio papio and critically endangered Cercopithecus roloway, as well as comparative data from other Cercopithecinae species, i.e. Allochrocebus lhoesti, Mandrillus sphinx and Papio anubis. Following collection from the epididymis, spermatozoa were measured for each species for the following parameters: head length, head width, head perimeter, head area, midpiece length and total flagellum length, and the head volume, ellipticity, elongation, roughness and regularity were then calculated. Our data are consistent with both the general morphology and the morphometric proportions of Cercopithecinae sperm. Some specificities were observed, with C. cephus displaying a narrow head (width = 2.76 ± 0.26 µM) and C. roloway displaying a short midpiece (6.65 ± 0.61 µM). This data set represents an important contribution, especially for Cercopithecus roloway, one of the most endangered monkeys in the world, and further data on additional specimens coupled to data on mating systems and reproductive ecology should allow a better understanding of the mechanisms underlying these morphological differences across primate species.

Same father, same face: Deep learning reveals selection for signaling kinship in a wild primate

Many animals rely on facial traits to recognize their kin; however, whether these traits have been selected specifically for this function remains unknown. Using deep learning for face recognition, we present the first evidence that interindividual facial resemblance has been selected to signal paternal kinship. Mandrills (Mandrillus sphinx) live in matrilineal societies, in which females spend their entire lives not only with maternal half-sisters (MHS) but also with paternal half-sisters (PHS). We show that PHS have more differentiated social relationships compared to nonkin, suggesting the existence of kin recognition mechanisms. We further demonstrate that facial resemblance increases with genetic relatedness. However, PHS resemble each other visually more than MHS do, despite both kin categories sharing similar degrees of genetic relatedness. This paternally derived facial resemblance among PHS indicates selection to facilitate kin recognition. This study also highlights the potential of artificial intelligence to study phenotypic evolution.

Divergent strategies in faeces avoidance between two cercopithecoid primates

Parasites constitute a major selective pressure which has shaped animal behaviour through evolutionary time. One adaption to parasites consists of recognizing and avoiding substrates or cues that indicate their presence. Among substrates harbouring infectious agents, faeces are known to elicit avoidance behaviour in numerous animal species. However, the function and mechanisms of faeces avoidance in non-human primates has been largely overlooked by scientists. In this study, we used an experimental approach to investigate whether aversion to faeces in a foraging context is mediated by visual and olfactory cues in two cercopithecoid primates: mandrills ( Mandrillus sphinx ) and long-tailed macaques ( Macaca fascicularis ). Visual and olfactory cues of faeces elicited lower food consumption rates in mandrills and higher food manipulation rates in long-tailed macaques. Both results support the infection-avoidance hypothesis and confirm similar tendencies observed in other primate species. More studies are now needed to investigate the divergence of avoidance strategies observed in non-human primates regarding food contamination.