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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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Observations of severe and lethal coalitionary attacks in wild mountain gorillas
Abstract In humans and chimpanzees, most intraspecific killing occurs during coalitionary intergroup conflict. In the closely related genus Gorilla, such behavior has not been described. We report three cases of multi-male, multi-female wild mountain gorilla ( G. beringei ) groups attacking extra-group males. The behavior was strikingly similar to reports in chimpanzees, but was never observed in gorillas until after a demographic transition left ~25% of the population living in large social groups with multiple (3+) males. Resource competition is generally considered a motivator of great apes’ (including humans) violent intergroup conflict, but mountain gorillas are non-territorial herbivores with low feeding competition. While adult male gorillas have a defensible resource (i.e. females) and nursing/pregnant females are likely motivated to drive off potentially infanticidal intruders, the participation of others (e.g. juveniles, sub-adults, cycling females) is harder to explain. We speculate that the potential for severe group disruption when current alpha males are severely injured or killed may provide sufficient motivation when the costs to participants are low. These observations suggest that the gorilla population’s recent increase in multi-male groups facilitated the emergence of such behavior, and indicates social structure is a key predictor of coalitionary aggression even in the absence of meaningful resource stress.
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- Award ID(s):
- 1552185
- PAR ID:
- 10426250
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 6
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/srep37018
