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Transient genital abnormalities in striped hyenas (Hyaena hyaena)
Aaron P Wagner1, Laurence G Frank, Scott Creel
1Department of Ecology, Montana State University, Bozeman, MT 59717, USA. apwagner@msu.edu
Hormones and Behavior
|April 20, 2007
Summary
Female spotted hyenas (Crocuta crocuta) possess highly masculinized genitalia. This study reveals similar genital development in striped hyenas (Hyaena hyaena), challenging social ecology-based theories for this unique trait.
Area of Science:
- Zoology
- Evolutionary Biology
- Mammalian Reproductive Anatomy
Background:
- Female spotted hyenas (Crocuta crocuta) exhibit unique, highly masculinized genitalia, with no external vagina, and all functions occurring through a clitoris resembling a penis.
- Previous explanations for this virilization focused on the social ecology specific to Crocuta, as it was the only known hyenid with such extreme external genital masculinization.
Purpose of the Study:
- To investigate genital development patterns in the striped hyena (Hyaena hyaena) and evaluate hypotheses for the evolution of genital masculinization in Hyaenidae.
- To determine if genital masculinization is a trait exclusive to highly social species or if it has deeper evolutionary roots within the family.
Main Methods:
- Comparative anatomical and hormonal analysis of male and female striped hyenas (Hyaena hyaena).
- Evaluation of existing evolutionary hypotheses for genital masculinization in light of new findings in Hyaena hyaena.
Main Results:
- Striped hyenas (Hyaena hyaena) display unusual similarity in male and female androgen concentrations.
- Transient genital anomalies were observed in young Hyaena hyaena, showing a convergence in genital appearance between sexes.
- These findings in the behaviorally solitary Hyaena hyaena do not support evolutionary models for masculinization solely based on high sociality.
Conclusions:
- Genital masculinization in Hyaenidae may not exclusively stem from the social ecology of species like Crocuta crocuta.
- The observed patterns in Hyaena hyaena suggest that masculinization in Crocuta could be an extreme elaboration of a pre-existing ancestral trait (homology).
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