Signaling in multiple modalities in male rhesus macaques: sex skin coloration and barks in relation to androgen levels, social status, and mating behavior

Abstract

The past decade has seen an increasing shift in animal communication towards more studies that incorporate aspects of signaling in multiple modalities. Although nonhuman primates are an excellent group for studying the extent to which different aspects of condition may be signaled in different modalities, and how such information may be integrated during mate choice, very few studies of primate species have incorporated such analyses. Here, we present data from free-ranging male rhesus macaques on sex skin coloration (modeled to receiver perception), bark vocal signals, androgen levels, morphometric variables, dominance status, and female mate choice. We show that, consistent with data on females, most intra- and interindividual variation in sex skin appearance occurs in luminance rather than color. Sex skin luminance was significantly correlated across different skin regions. Sex skin luminance did not correlate with the majority of bark parameters, suggesting the potential for the two signals to convey different information. Sex skin appearance was not related to androgen levels although we found some evidence for links between androgen levels and bark parameters, several of which were also related to morphometric variables. We found no evidence that either signal was related to male dominance rank or used in female mate choice, though more direct measures of female proceptive behavior are needed. Overall, the function of male sex skin coloration in this species remains unclear. Our study is among the first nonhuman primate studies to incorporate measurements of multiple signals in multiple modalities, and we encourage other authors to incorporate such analyses into their work.

Color in competition contexts in non-human animals

“…The authors interpret this evidence as evidence that red signals dominance in the macaques (Khan et al, 2011). However, this interpretation conflicts with the results of the observational studies described above, where red does not correlate with rank (Higham et al, 2013).…”

“…comm. in Vandenburgh, 1965), a recent study found no evidence that red coloration is linked to rank or to androgen levels during the mating season (Higham et al, 2013). No experimental studies have yet been published that examine male-male relationships in relation to red in rhesus macaques, although adult males do attend to female red coloration (Higham et al, 2011;Waitt et al, 2006).…”

“…This weaker relationship allows for the possibility that the face and hindquarters may encode different information (Higham et al, 2013), possibly mediated via tissue-specific differences in enzyme activity or receptor populations, as suggested for mandrills (Setchell & Dixson, 2001c).…”

“…As in mandrills and drills, the red colour of the three body regions in rhesus macaques correlates positively both between and within individuals for face/genitalia and genitalia/hindquarters comparisons, although only within individuals for face/hindquarters comparisons (Higham et al, 2013). This weaker relationship allows for the possibility that the face and hindquarters may encode different information (Higham et al, 2013), possibly mediated via tissue-specific differences in enzyme activity or receptor populations, as suggested for mandrills (Setchell & Dixson, 2001c).…”

“…The degree of coloration is highly variable among individuals (Rhodes et al, 1997;Waitt, Gerald, 13 Little, & Kraiselburd, 2006), ranging from light pink to dark red, with more variation in genital colour than on the face or rump (Higham, Pfefferle, Heistermann, Maestripieri, & Stevens, 2013). Castration causes a decline in skin colour, although it does not reach normal body skin colour, possibly due to adrenal androgens (Vandenburgh, 1965).…”