Abstract
In the animal kingdom, conspicuous colors are often used for inter- and intra-sexual communication. Even though primates are the most colorful mammalian taxon, many questions, including what potential information color signals communicate to social partners, are not fully understood. Vervet monkeys (Chlorocebus pygerythrus) are ideal to examine the covariates of color signals. Males have multi-colored genitals, which they present during distinctive male-male interactions, known as the “Red-White-and-Blue” (RWB) display, but the genitals are also visible across a variety of other contexts, and it is unclear what this color display signals to recipients. We recorded genital color presentations and standardized digital photos of male genitals (N = 405 photos) over one mating season for 20 adult males in three groups at the Samara Private Game Reserve, South Africa. We combined these with data on male characteristics (dominance, age, tenure length, injuries, and fecal glucocorticoid metabolite concentrations). Using visual modeling methods, we measured single colors (red, white, blue) but also the contrasts between colors. We assessed the frequency of the RWB genital display and male variation in genital coloration and linked this to male characteristics. Our data suggest that the number of genital displays increased with male dominance. However, none of the variables investigated explained the inter- and intra-individual variation in male genital coloration. These results suggest that the frequency of the RWB genital display, but not its color value, is related to dominance, providing valuable insights on covariation in color signals and their display in primates.Significance statementConspicuous colors in animals often communicate individual quality to mates and rivals. By investigating vervet monkeys, a primate species in which males present their colorful genitals within several behavioral displays, we aim to identify the covariates of such colorful signals and their behavioral display. Using visual modeling methods for the color analysis and combining behavioral display data and color data with male characteristics, we found that high-ranking males displayed their colorful genitals more frequently than lower-ranking ones. In contrast, color variation was not influenced by male dominance, age, tenure length, or health. Our results can serve as a basis for future investigations on the function of colorful signals and behavioral displays, such as a badge of status or mate choice in primates.
Highlights
Ornaments or decorative traits such as colorful plumage, fur, and skin have evolved across the animal kingdom for use in, for example, mate choice and male-male competition (Berglund et al 1996)
There is a large body of literature demonstrating that many colorful ornaments and signals are linked to sexual selection, with signal evolution driven by mate choice and/or male-male competition
We recorded all occurrences of the physical action whereby a male lifted his tail and exposed the genitals, the red perianal area, and the blue scrotum completely, irrespective of the context or to which sex it was shown. We refer to this as the RWB genital display hereafter. We examined both the distribution of genital displays across contexts and whether RWB genital display frequency was related to male characteristics, including genital colors, dominance rank, and group tenure
Summary
Ornaments or decorative traits such as colorful plumage, fur, and skin have evolved across the animal kingdom for use in, for example, mate choice and male-male competition (Berglund et al 1996). There is a large body of literature demonstrating that many colorful ornaments and signals are linked to sexual selection, with signal evolution driven by mate choice and/or male-male competition (e.g., reviewed in Caro 2005; Hill 2006; Senar 2006; Price et al 2008). Skin color variation in reptiles is associated with body mass and corticosterone levels (Fitze et al 2009). The dark mane of male lions (Panthera leo) is associated with higher levels of testosterone compared to lighter-maned males (West and Packer 2002)
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