Chemical Composition of Scent-Gland Secretions in an Old World Monkey (Mandrillus sphinx): Influence of Sex, Male Status, and Individual Identity

Abstract

Primates are traditionally considered to be microsmatic, with decreased reliance on olfactory senses in comparison to other sensory modalities such as vision. This is particularly the case for Old World monkeys and apes (catarrhines). However, various lines of evidence suggest that chemical communication may be important in these species, including the presence of a sternal scent-gland in the mandrill. We investigated the volatile components of mandrill odor using gas chromatography-mass spectrometry. We identified a total of 97 volatile components in 88 swabs of the sternal gland secretion and 95 samples of sternal gland hair saturated with scent-gland secretion collected from 27 males and 18 females. We compared odor profiles with features of the signaler using principle components and discriminant function analyses and found that volatile profiles convey both variable (age, dominance rank in males) and fixed (sex, possibly individual identity) information about the signaler. The combination of an odor profile that signals sex, age, and rank with increased motivation to scent-mark and increased production of secretion in high-ranking males leads to a potent signal of the presence of a dominant, adult male with high testosterone levels. This may be particularly relevant in the dense Central African rain forest which mandrills inhabit. By contrast, we were unable to differentiate between either female cycle stage or female rank based on odor profiles, which accords with behavioral studies suggesting that odor signals are not as important in female mandrills as they are in males. The similarity of our findings to those for other mammals and in primates that are more distantly related to humans suggests a broader role for odor in primate communication than is currently recognized.

Odour signals major histocompatibility complex genotype in an Old World monkey

“…The sex differences that we identified in odour signal diversity build on our previous analyses in which we found that we could reliably discriminate male and female odour profiles using DFA [33], and suggest that sex differences in odour profiles are owing to differences in how the chemical diversity is distributed among the different compounds that comprise the signal, rather than to differences in the number of compounds present. This provides an interesting comparison with ring-tailed lemurs, where female odour contains more compounds than male's [28], and reflects differences in the social system of the two species.…”

“…We retained PCs with eigenvalues greater than 1 (15 PCs for swabs, explaining a total 79.3% of the variance; 18 PCs for hair samples, explaining a total 76.8% of the variance; [33]). We used these PCs as covariates in discriminant function analysis (DFA) to examine the relationship between odour and MHC genotype, grouping samples using possession of individual supertypes (present/absent for each).…”

“…Both male and female mandrills possess a sternal gland, unlike most Old World monkeys. Volatile odour profiles of the sternal gland secretion differ according to both variable (age, dominance rank in males) and fixed (sex, possibly individual identity) features of the signaller [33]. MHC-diverse males have higher reproductive success, and mandrills reproduce preferentially with MHC dissimilar individuals [34].…”

The hidden benefits of sex: Evidence for MHC‐associated mate choice in primate societies

“…In parallel, a resurgence of interest in primate olfactory capacities provides further support for the idea that chemical cues play a role in communication in all major primate radiations [49,53,54]. Analyses of the content of chemical signals suggest that they can advertise individual traits in ring-tailed lemurs [42], mandrills [55] and humans [56]. Moreover, odour signals genome-wide diversity and genetic relatedness in ringtailed lemurs [42,57] and mandrills [58], as well as MHC diversity and dissimilarity in mandrills [58].…”

Color in competition contexts in non-human animals

“…For example, colour in mandrills is part of a suite of visual, olfactory and acoustic traits (Darwin, 1871;Osman Hill, 1970). While male mandrill colour and odour both signal age and rank, they also reflect different aspects of the male: red signals testosterone and some MHC genotypes, while odour encodes genetic diversity and genetic similarity (Setchell et al, 2011(Setchell et al, , 2009Setchell, Vaglio, et al, 2010). Similarly, red colour and barks in male rhesus macaques have the potential to convey different information to the perceiver (Higham et al, 2013).…”