Platyrrhine color signals: New horizons to pursue

Abstract

Like catarrhines, some platyrrhines show exposed and reddish skin, raising the possibility that reddish signals have evolved convergently. This variation in skin exposure and color combined with sex-linked polymorphic color vision in platyrrhines presents a unique, and yet underexplored, opportunity to investigate the relative importance of chromatic versus achromatic signals, the influence of color perception on signal evolution, and to understand primate communication broadly. By coding the facial skin exposure and color of 96 platyrrhines, 28 catarrhines, 7 strepsirrhines, 1 tarsiiform, and 13 nonprimates, and by simulating the ancestral character states for these traits, we provide the first analysis of the distribution and evolution of facial skin exposure and color in platyrrhini. We highlight ways in which studying the presence and use of color signals by platyrrhines and other primates will enhance our understanding of the evolution of color signals, and the forces shaping color vision.

Keywords: New World monkeys; chroma; color vision; communication; luminance; skin.

Figure 1

Examples of exposed facial skin in platyrrhine monkeys. Golden lion tamarins (Leontopithecus rosalia, a); red‐faced spider monkey (Ateles paniscus, b); and bald‐headed uakari (Cacajao calvus, c). Photo credits: Jeroen Kransen (a), Dan Sloan (b), and Marc Wisniak (c)

Figure 2

Examples of categories of exposed skin in primates. Completely exposed face (cheeks, nose, eyes, forehead), a, b); exposed skin around the eyes, nose, and mouth, c, d); exposed skin around the nose and eyes; or exposed skin around the nose and mouth, e, f); exposed skin around eyes, g, h); exposed skin around the nostrils, i, j). Photo credits: Marc Wisniak (a), Zyance (b), David M. Jensen (c), David V. Raju (d), Frank Wouters (e), Fabio Manfredini (f), Leszek Leszczynski (g), Halley Pacheco de Oliveira (h), Brocken Inaglory (i), and Jik jik (j)

Figure 3

Examples of categories of skin color in primates. Depigmented (Cebus capucinus), a); hypervasculated (Cacajao calvus), b); mottled (Brachyteles hypoxanthus), c); hyperpigmented (Alouatta pigra), d). Photo credits: Steven G. Johnson (a), Kevin O'Connel (b), Peter Schoen (c), and Dave Johnson (d)

Figure 4

Ancestral state reconstruction of skin exposure visualized on a phylogeny of primates using Maximum Likelihood under the Ornstein‐Uhlenbeck (OU) model. The phylogenetic tree was redrawn from70 and adapted to include 96 platyrrhines, along with 28 catarrhines, 7 strepsirrhines, 1 tarsiiform, and 13 nonprimate groups to reconstruct ancestral types. The color map represents observed and reconstructed ancestral states for skin exposure ranging from a completely exposed face (brown) to only exposed skin on the nose (green)

Figure 5

Ancestral state reconstruction of skin color visualized on a phylogeny of primates using 1,000 stochastic character maps under the Equal Rates (ER) model. The phylogenetic tree was redrawn from70 and adapted to include 96 platyrrhines, along with 28 catarrhines, 7 strepsirrhines, 1 tarsiiform, and 13 nonprimate groups to reconstruct ancestral types. Branch colors represent posterior probability densities of the skin color states along the edges and pie charts show the relative probabilities of each state at the internal nodes. Pink indicates depigmented skin, red indicates hypervasculated skin, light blue indicates mottled skin, and dark blue indicates hyperpigmented skin. Images of hypervasculated skin are shown on the right of the species names. Photo credits: Marc Wisniak (Cacajao calvus), Valdir Hobus (Chiropotes albinasus), Kitty Terwolbeck (Ateles paniscus) and David Raju (Macaca mulatta)

Figure 6

Conspicuous scrotum relative to body pelage in mantled howler monkey (Alouatta palliata, a) and bearded saki (Chiropotes satanas, b). Photo credits: Scott Robinson (a) and Allan Hopkins (b)

Figure 7

Simulated appearance of a female rhesus macaque (Macaca mulatta; Cayo Santiago) for: a trichromatic observer (a); a dichromatic observer (b).80 Peak cone sensitivity values on simulations of trichromatic Rhesus macaque vision (S cone = 420 nm; M cone = 530 nm; L cone = 560 nm) and a protanomalous dichromatic type (S cone = 420 nm; M cone = 530 nm).45 Photo by ADM