Fruits, foliage and the evolution of primate colour vision

Abstract

Primates are apparently unique amongst the mammals in possessing trichromatic colour vision. However, not all primates are trichromatic. Amongst the haplorhine (higher) primates, the catarrhines possess uniformly trichromatic colour vision, whereas most of the platyrrhine species exhibit polymorphic colour vision, with a variety of dichromatic and trichromatic phenotypes within the population. It has been suggested that trichromacy in primates and the reflectance functions of certain tropical fruits are aspects of a coevolved seed-dispersal system: primate colour vision has been shaped by the need to find coloured fruits amongst foliage, and the fruits themselves have evolved to be salient to primates and so secure dissemination of their seeds. We review the evidence for and against this hypothesis and we report an empirical test: we show that the spectral positioning of the cone pigments found in trichromatic South American primates is well matched to the task of detecting fruits against a background of leaves. We further report that particular trichromatic platyrrhine phenotypes may be better suited than others to foraging for particular fruits under particular conditions of illumination; and we discuss possible explanations for the maintenance of polymorphic colour vision amongst the platyrrhines.

Evolution of colour vision in mammals

“…In recent years, a number of computational models of colour vision have been employed to test whether the primate M/L pigments are well suited to underlie the discrimination of fruits embedded in foliage. The consistent answer is that they are (Osorio & Vorobyev 1996;Regan et al 2001;Parraga et al 2002). However, model computations also show that there are other classes of critical behaviours, for example discrimination of edible foliage or of variations in skin coloration, which would be similarly well served by the M/L dimension of primate colour vision Changizi et al 2006).…”

“…Research conducted in recent years has greatly advanced our understanding of the distribution and evolution of primate colour vision. References to the now numerous original articles on these topics can be found in several recent reviews (Regan et al 2001;Osorio et al 2004;Jacobs 2007Jacobs , 2008.…”

“…It is a long-held idea that since many primates are frugivores, and since ripened fruits can offer distinctive chromatic signals, the evolution of the dimension of primate colour vision supported by M/L pigments is causally linked to the harvest of fruits (e.g. Regan et al 2001). In recent years, a number of computational models of colour vision have been employed to test whether the primate M/L pigments are well suited to underlie the discrimination of fruits embedded in foliage.…”

Bare skin, blood and the evolution of primate colour vision

“…) We should emphasize that the idea that colour vision is important for colour signalling is not new (e.g. Hingston 1933;Wickler 1967;Regan et al 2001;Liman & Innan 2003;Waitt et al 2003;Zhang & Webb 2003), except that typically it is assumed that colour vision was originally selected for some other reason. One of the main contributions we make here is the argument that colour vision is near-optimal for discriminating skin colour modulations, something that increases the prima facie plausibility of the hypothesis that trichromacy was originally selected for the perception of skin colour signalling.…”

“…Other adaptive explanations have been put forth to explain primate colour vision, including advantages for frugivory (Allen 1879;Mollon 1989;Osorio & Vorobyev 1996;Regan et al 2001;Surridge & Mundy 2002), and for folivory (Lucas et al 2003). Our discussion here provides no answer as to which of these may more likely have been the original selection pressure for trichromacy, or whether all these hypotheses may be important contributors (Regan et al 2001). One advantage of the skin colour-signalling hypothesis is that, whereas there is a wide variety of trichromat frugivory and folivory behaviour, skin colour modulation is due to fundamental properties of blood shared by all primates, and this could be key in understanding the universal M and L cone sensitivities of routine trichromats.…”