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Abstract Androgens are important mediators of male‐male competition in many primate species. Male gorillas' morphology is consistent with a reproductive strategy that relies heavily on androgen‐dependent traits (e.g., extreme size and muscle mass). Despite possessing characteristics typical of species with an exclusively single‐male group structure, multimale groups with strong dominance hierarchies are common in mountain gorillas. Theory predicts that androgens should mediate their dominance hierarchies, and potentially vary with the type of group males live in. We validated the use of a testosterone enzyme immunoassay (T‐EIA R156/7, CJ Munro, UC‐Davis) for use with mountain gorilla fecal material by (1) examining individual‐level androgen responses to competitive events, and (2) isolating assay‐specific hormone metabolites via high‐performance liquid chromatography. Males had large (2.6‐ and 6.5‐fold), temporary increases in fecal androgen metabolite (FAM) after competitive events, and most captured metabolites were testosterone or 5α‐dihydrotestosterone‐like androgens. We then examined the relationship between males' dominance ranks, group type, and FAM concentrations. Males in single‐male groups had higher FAM concentrations than males in multimale groups, and a small pool of samples from solitary males suggested they may have lower FAM than group‐living peers. However, data from two different time periods (n = 1610 samples) indicated there was no clear relationship between rank and FAM concentrations, confirming results from the larger of two prior studies that measured urinary androgens. These findings highlight the need for additional research to clarify the surprising lack of a dominance hierarchy/androgen relationship in mountain gorillas.
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Social and demographic correlates of male androgen levels in wild white‐faced capuchin monkeys ( Cebus capucinus )
The Challenge Hypothesis, designed originally to explain the patterning of competitive behavior and androgen levels in seasonally breeding birds, predicts that males will increase their androgen levels in order to become more competitive in reproductive contexts. Here we test predictions derived from the Challenge Hypothesis in white‐faced capuchin monkeys (Cebus capucinus), a species that has somewhat seasonal reproduction. We analyzed demographic and hormonal data collected over a 5.25‐year period, from 18 males in nine social groups living in or near Lomas Barbudal Biological Reserve, Costa Rica. Alpha males had higher androgen levels than subordinates. Contrary to our predictions, neither the number of breeding‐age males nor the number of potentially fertile females was obviously associated with androgen levels. Furthermore, male androgen levels were not significantly linked to social stability, as measured by stability of male group membership or recency of change in the alpha male position. Androgen levels changed seasonally, but not in a manner that had an obvious relationship to predictions from the Challenge Hypothesis: levels were generally at their lowest near the beginning of the conception season, but instead of peaking when reproductive opportunities were greatest, they were at their highest near the end of the conception season or shortly thereafter. This lack of correspondence to the timing of conceptions suggests that there may be ecological factors not yet identified that influence ifA levels. We expected that the presence of offspring who were young enough to be vulnerable to infanticide during an alpha male takeover might influence androgen levels, at least in the alpha male, but this variable did not significantly impact results.
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- PAR ID:
- 10034792
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Primatology
- Volume:
- 79
- Issue:
- 7
- ISSN:
- 0275-2565
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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