Arrested development of secondary sexual adornments in subordinate adult male mandrills (Mandrillus sphinx).

Setchell, J.M.; Dixson, A.F.

Abstract

Previous studies of semifree-ranging mandrills identified two morphological and social variants of the adult male, based on behavioral and secondary sexual characteristics. Fatted males are social, with highly developed sex skin coloration, large testes, high plasma testosterone levels, and fat rumps; while nonfatted males are peripheral or solitary, with paler sex skin, smaller testes, lower plasma testosterone, and slimmer rumps. We present a detailed study of morphology and group association for 10 adult male mandrills, living in two semifree-ranging groups in Gabon, in order to relate differences between males to dominance rank. The results show that rather than existing as two distinct morphotypes, male mandrills represent a continuous spectrum of possibilities between social males with fully developed secondary sexual characteristics, and solitary males with muted secondary sexual characteristics. Alpha males (N = 2) had the highest testosterone levels, the most colorful sex skin, and the most active sternal glands, and were the only males to spend 100% of their time with the social group. Rank relationships between nonalpha males (N = 8) were not always clear, but all subordinate males had lower testosterone levels and less development of the secondary sexual adornments, and were less group-associated than alpha males. These findings suggest that only alpha males have sufficient testosterone to develop full secondary sexual characteristics, and we propose possible socioendocrine mechanisms underlying the suppression of testosterone and secondary sexual development in subordinate adults. We discuss differences in secondary sexual development in relation to reproductive strategies, and discuss the evolution of alternative reproductive morphs in primates.

Citation

Setchell, J., & Dixson, A. (2001). Arrested development of secondary sexual adornments in subordinate adult male mandrills (Mandrillus sphinx). American journal of physical anthropology, 115, 245-252. https://doi.org/10.1002/ajpa.1079

• Journal Article Type: Article
• Publication Date: 2001
• Journal: American Journal of Physical Anthropology
• Print ISSN: 0002-9483
• Electronic ISSN: 1096-8644
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 115
• Pages: 245-252
• DOI: https://doi.org/10.1002/ajpa.1079
• Keywords: socioendocrinology; dominance rank; testosterone; sexual skin; alternative strategies
• Public URL: https://durham-repository.worktribe.com/output/1565051