Signaling in multiple modalities in male rhesus macaques: sex skin coloration and barks in relation to androgen levels, social status, and mating behavior
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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.
KeywordsColoration Luminance Vocal signals Multimodal Primate Rhesus macaques
We thank Doreen Hess, Jenna Goldfein, Maria Rakhovskaya, and the staff of the Caribbean Primate Research Center for logistical support in the field and assistance with animal capturing and handling. We are extremely grateful to Andrea Heistermann and Petra Kiesel for analyzing the fecal samples and to Tara Mandalaywala and the Caribbean Primate Research Center for assisting with their transportation to Germany. We are also most grateful to John Addicott for first helping us to develop our behavioral data parser and Access database. We additionally thank Kurt Hammerschmidt for making his LMA sound analysis program available. Eileen Hebets and two anonymous reviewers provided constructive and helpful comments on the manuscript. This research was supported by NIH grant R21-AG029862 to D.M. M.S. was supported by a Biotechnology and Biological Sciences Research Council David Phillips Research Fellowship (BB/G022887/1). This publication was made possible by grant number CM-5-P40RR003640 from the NIH National Center for Research Resources (NCRR) to the Caribbean Primate Research Center of the University of Puerto Rico. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of NCRR or NIH.
This study was conducted in accordance with the NIH Guide for the Care and Use of Laboratory Animals and conformed to all laws of Puerto Rico, the USA, and Germany. The protocol for this study was approved by the Institutional Animal Care and Use Committee, Medical Sciences Department, University of Puerto Rico.
Conflict of interest
The authors declare no conflict of interest.
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