Biomedical and clinical sciences are experiencing a renewed interest in the fact that males and females differ in many anatomic, physiological, and behavioral traits. Sex differences in trait variability, however, are yet to receive similar recognition. In medical science, mammalian females are assumed to have higher trait variability due to estrous cycles (the 'estrus-mediated variability hypothesis'); historically in biomedical research, females have been excluded for this reason. Contrastingly, evolutionary theory and associated data support the 'greater male variability hypothesis'. Here, we test these competing hypotheses in 218 traits measured in >26,900 mice, using meta-analysis methods. Neither hypothesis could universally explain patterns in trait variability. Sex-bias in variability was trait-dependent. While greater male variability was found in morphological traits, females were much more variable in immunological traits. Sex-specific variability has eco-evolutionary ramifications including sex-dependent responses to climate change, as well as statistical implications including power analysis considering sex difference in variance.
- Shinichi Nakagawa
- Jeremy Mason
- Alistair M Senior
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Rosalyn Gloag, University of Sidney, Australia
- Received: September 16, 2020
- Accepted: October 30, 2020
- Accepted Manuscript published: November 17, 2020 (version 1)
? 2020, Zajitschek et al.
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