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Selective breeding for a behavioral trait changes digit ratio.

Reginia H Y Yan¹, Jessica L Malisch, Robert M Hannon

¹Department of Psychology, University of Alberta, Edmonton, Alberta, Canada.

|September 18, 2008

Summary

This summary is machine-generated.

The 2D:4D digit ratio, often linked to prenatal androgens, unexpectedly increased in mice bred for exercise. This challenges its use as a sole indicator of prenatal hormone exposure, suggesting other factors may be involved.

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Area of Science:

Endocrinology
Behavioral Genetics
Comparative Anatomy

Background:

The 2D:4D digit ratio (second digit length / fourth digit length) is a proposed marker for prenatal androgen exposure.
In humans, a lower 2D:4D ratio correlates with higher physical fitness and sporting ability.
Previous studies suggested 2D:4D variation in mice relates to uterine environment and behavior.

Purpose of the Study:

To investigate the effect of selective breeding for voluntary exercise on the 2D:4D digit ratio in mice.
To examine whether changes in 2D:4D in mice align with human correlations to physical fitness and prenatal hormone exposure.

Main Methods:

Selective breeding of four mouse lines for increased voluntary wheel running over multiple generations.
Measurement of 2D:4D digit ratios in the selected mouse lines.
Assessment of correlated changes in aerobic capacity, corticosterone levels, and predatory aggression.

Main Results:

Selective breeding for voluntary exercise significantly increased the 2D:4D digit ratio in mice.
This increase in 2D:4D (apparent "feminization") occurred alongside enhanced aerobic capacity and corticosterone levels.
The observed "feminization" in mice contradicts the "masculinization" trend seen in physically fit humans.

Conclusions:

The 2D:4D digit ratio in mice selected for exercise is not a reliable proxy for prenatal androgen exposure.
The results suggest that 2D:4D may be influenced by glucocorticoids or other regulatory factors.
Further research is needed to elucidate the complex hormonal and genetic underpinnings of digit ratio variation.