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Male reproductive success is determined by the interplay of female mate choice and male–male competition, often linked to dominance rank in social animals. Across taxa, elaborate ornaments, such as bright coloration or large antlers, often function as badges of status, signalling male competitive ability to rivals. In species where females mate with multiple males, post-mating sperm competition also plays an important role in male reproductive success and is associated with larger relative testes size. We investigate the relationship between morphological features and dominance rank in wild male white-faced capuchins. Using parallel-laser photogrammetry, we measured aspects of facial morphology, including facial width-to-height ratio, and testes size. We found that alpha males had significantly larger facial width-to-height ratios, wider faces and wider scrota than subordinate males. These results suggest that facial traits potentially function as badges of status in male white-faced capuchins and may play a role in pre-mating competition and/or mate choice, while differences in scrotal size reflect adaptations for post-mating competition. This study highlights the under-recognized role of facial trait evolution in sexual selection among relatively gracile yet highly visually oriented mammals and the potential variability of sexual traits in species characterized by strong reproductive skew among males.
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Black and orange coloration predict success during male–male competition in the guppy
Abstract Investigating how intrasexual competition and intersexual mate choice act within a system is crucial to understanding the maintenance and diversity of sexually-dimorphic traits. These two processes can act in concert by selecting for the same trait, or in opposition by selecting for different extremes of the same trait; they can also act on different traits, potentially increasing trait complexity. We asked whether male–male competition and female mate choice act on the same male traits using Trinidadian guppies, which exhibit sexual size dimorphism and male-limited color patterns consisting of different colors arranged along the body and fins. We used behavioral assays to assess the relationship between color and competitive success and then compared our results to the plethora of data on female choice and color in our study population. Males initiated more contests if they were larger than their competitor. Males won contests more often if they had more black coloration than their competitor, and the effect of black was stronger when males had less orange than their competitor. Additionally, males won more often if they had either more structural color (iridescence) and more orange, or less structural color and less orange than their competitor, suggesting multiple combinations of color traits predict success. Females from our study population exhibit a strong preference for more orange coloration. Thus, traits favored in male contests differ from those favored by intersexual selection in this population. These results suggest that inter- and intrasexual selection, when acting concurrently, can promote increased complexity of sexually selected traits.
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- Award ID(s):
- 1740466
- PAR ID:
- 10406957
- Editor(s):
- Briffa, Mark
- Date Published:
- Journal Name:
- Behavioral Ecology
- Volume:
- 33
- Issue:
- 6
- ISSN:
- 1045-2249
- Page Range / eLocation ID:
- 1196 to 1206
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1093/beheco/arac093
