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Latitudinal distribution, migration, and testosterone levels in birds.
L Z Garamszegi1, K Hirschenhauser, V Bókony
1Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610 Wilrijk, Belgium. laszlo.garamszegi@ua.ac.be
The American Naturalist
|August 30, 2008
Summary
Higher latitude birds have higher testosterone (T) levels, linked to migration and breeding synchrony. These factors increase male-male competition, driving T levels despite latitude being the strongest predictor.
Area of Science:
- * Comparative endocrinology and evolutionary biology.
- * Investigating hormonal adaptations in avian species across different latitudes.
Background:
- * Tropical bird species typically exhibit lower testosterone (T) levels during breeding seasons compared to temperate species.
- * The underlying mechanisms for the observed positive correlation between testosterone and latitude in birds are not well understood.
- * Previous research indicates a general trend of higher T levels in temperate zone birds.
Purpose of the Study:
- * To explore the role of social constraints, specifically male-male competition influenced by migration and breeding synchrony, in explaining latitude-based differences in testosterone levels.
- * To determine if migration and breeding synchrony mediate the relationship between latitude and peak testosterone titers in avian species.
Main Methods:
- * A comparative analysis was conducted across over 100 bird species.
- * Data on migration patterns, breeding season length, breeding synchrony, and peak testosterone levels were collected and analyzed.
- * Multivariate statistical models were employed to control for covariation among predictor variables.
Main Results:
- * Peak testosterone levels were significantly associated with species that migrate and those with shorter, more synchronous egg-laying periods.
- * Migration and breeding synchrony were found to be related to a species' latitudinal distribution.
- * Latitude remained the most significant predictor of peak testosterone levels, even after accounting for migration and breeding synchrony.
Conclusions:
- * Migration and breeding synchrony appear to be significant factors contributing to the latitude effect on testosterone levels in birds.
- * These factors likely exert their influence by intensifying intrasexual competition during breeding seasons.
- * While social constraints play a role, other geographically varying factors may also influence testosterone levels across latitudes.
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