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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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This content will become publicly available on January 16, 2026
Male bluegill vary in color and behavior relative to their position in a lek
Animals organize into social groups to increase collective fitness. These groups use behavior and morphological traits like color to communicate social status. Male bluegill (Lepomis macrochirus) form breeding collectives during the reproductive months. However, whether these colonies generate resource-stratified social hierarchies to manage intrasexual competition is unknown. We hypothesize that territorial position within the colony results in different body colors and behavioral profiles. To test this hypothesis, we quantified color patterns in wild communities of bluegill using computer vision, scored the behavior of lek occupying parental males, and categorically classified lek position as a function of neighboring males. From these data, we show that body coloration and behavior vary with lek position, suggesting a division of labor in the construction and maintenance of grouped territories where courtship and sexual selection take place. Collectively, these data underline the importance of male-specific morphological plasticity and its impacts on social organization.
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- Award ID(s):
- 1921773
- PAR ID:
- 10568652
- Editor(s):
- Petrulis, Aras
- Publisher / Repository:
- Frontiers in Ethology
- Date Published:
- Journal Name:
- Frontiers in Ethology
- Edition / Version:
- 1
- Volume:
- 3
- ISSN:
- 2813-5091
- Subject(s) / Keyword(s):
- coloration lek behavior Lepomis social behavior bluegill Lepomis machrochirus body coloration lek attendance
- Format(s):
- Medium: X Size: 1.9MB Other: pdf
- Size(s):
- 1.9MB
- Sponsoring Org:
- National Science Foundation
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