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Testosterone, testes size, and mating success in birds: a comparative study
L Z Garamszegi1, M Eens, S Hurtrez-Boussès
1Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610 Wilrijk, Belgium. laszlo.garamszegi@ua.ac.be
Hormones and Behavior
|March 22, 2005
Summary
Testosterone levels in male birds are linked to mating strategies. While social mating success is influenced by latitude, higher testosterone is associated with extra-pair paternity, suggesting a role in sperm competition.
Area of Science:
- Evolutionary biology
- Animal behavior
- Endocrinology
Background:
- Reproductive behaviors in vertebrates are regulated by hormone secretion patterns.
- Testosterone's role in sexual selection, particularly concerning polygyny and extra-pair paternity, requires further investigation.
Purpose of the Study:
- To test the hypothesis that increased levels of testosterone are crucial for sexual selection in male birds.
- To examine the relationship between testosterone levels, polygyny, extra-pair paternity, and latitudinal distribution across bird species.
Main Methods:
- Comparative analyses of 116 bird species using Generalized Least Squares Models.
- Assessment of circulating testosterone levels, including peak and residual peak testosterone.
- Evaluation of mating success metrics (polygyny, extra-pair paternity) and relative testes size.
Main Results:
- Weak positive phylogenetic correlations between testosterone and social mating success were confounded by latitudinal distribution.
- A significant positive relationship was found between peak/residual peak testosterone and extra-pair paternity, independent of latitude.
- Relative testes size was positively associated with peak and residual testosterone, indicating a link to sperm competition.
Conclusions:
- Testosterone levels are differentially affected by social and sexual mating pressures, with latitude mediating social mating influences.
- Sperm competition, driven by relative testes size, plays a significant role in the evolution of reproductive mechanisms and testosterone levels in birds.