Catarrhine photopigments are optimized for detecting targets against a foliage background

The colour vision of many primates is trichromatic, whereas that of all other mammals is thought to be dichromatic or monochromatic. Moreover, the triplets of cone pigments in different catarrhines (Old World apes and monkeys) are strikingly similar in their spectral positions. We ask whether the selective advantage of trichromacy lies in an enhanced ability to find edible leaves or fruit. Further, we ask whether any factor in these two search tasks has constrained the particular set of cone spectral sensitivities observed in all catarrhines. We measured the spectral properties of the natural environments of six primate species in Uganda: Pan troglodytes, Cercopithecus mitis, Cercopithecus ascanius, Lophocebus albigena, Colobus guereza and Colobus badius. We concentrated on the fruit and leaves in their diets and the leaves of the trees that make up the background against which these diet items must be found. We plotted these measured stimuli in colour spaces appropriate for each primate species, and found that both frugivory and folivory are facilitated by the extra dimension of colour vision found in catarrhines but lacking in most other mammals. Furthermore, by treating the task of searching for food as a signal-detection task, we show that, of all possible combinations of cone sensitivities, the spectral positions of the actual primate pigments are optimal for finding fruit or young leaves against the background of mature leaves. This is because the variance of the chromaticities of the mature leaves is minimised in one channel of the primate's colour vision, so allowing anything that is not a mature leaf to stand out.

Papio cynocephalus Endogenous Retrovirus among Old World Monkeys: Evidence for Coevolution and Ancient Cross-Species Transmissions

ABSTRACT To study the evolutionary history of Papio cynocephalus endogenous retrovirus (PcEV), we analyzed the distribution and genetic characteristics of PcEV among 17 different species of primates. The viral pol-env and long terminal repeat and untranslated region (LTR-UTR) sequences could be recovered from all Old World species of the papionin tribe, which includes baboons, macaques, geladas, and mangabeys, but not from the New World monkeys and hominoids we tested. The Old World genera Cercopithecus andMiopithecus hosted either a PcEV variant with an incomplete genome or a virus with substantial mismatches in the LTR-UTR. A complete PcEV was found in the genome of Colobus guereza—but not in Colobus badius—with a copy number of 44 to 61 per diploid genome, comparable to that seen in papionins, and with a sequence most closely related to a virus of the papionin tribe. Analysis of evolutionary distances among PcEV sequences for synonymous and nonsynonymous sites indicated that purifying selection was operational during PcEV evolution. Phylogenetic analysis suggested that possibly two subtypes of PcEV entered the germ line of a common ancestor of the papionins and subsequently coevolved with their hosts. One strain of PcEV was apparently transmitted from a papionin ancestor to an ancestor of the central African lowland C. guereza.