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The relationship between sexual dimorphism and intersex correlation: do models support intuition?
Gemma Puixeu1, Laura Katherine Hayward1
1Institute of Science and Technology Austria, Klosterneuburg 3400, Austria.
Genetics
|August 21, 2025
Summary
The study reveals that the relationship between genetic correlation and sexual dimorphism is not always negative. Models show that shared genetic architecture can increase or decrease trait differences between sexes, depending on selection pressures.
Area of Science:
- Evolutionary genetics
- Quantitative genetics
- Sexual selection
Background:
- Sexual dimorphism (SD) is the difference in average trait values between males and females.
- It is often assumed that SD is constrained by shared genetic architecture, leading to a negative correlation with intersex genetic correlation (r fm).
- Existing theories suggest SD and r fm are negatively correlated due to constraints on sex-specific selection or selection reducing r fm.
Purpose of the Study:
- To investigate the relationship between intersex genetic correlation (r fm) and sexual dimorphism (SD).
- To explore the conditions under which a correlation between r fm and SD arises.
- To provide a mechanistic framework for understanding inconsistent empirical findings on SD and r fm.
Main Methods:
- Development of theoretical models incorporating sex-specific stabilizing selection, mutation, and genetic drift.
- Analysis of the interplay between genetic architecture and evolutionary forces shaping trait differences between sexes.
- Quantification of the effect of genetic drift on non-zero SD even with identical selection.
Main Results:
- Contrary to common assumptions, models demonstrate that mechanisms thought to generate a negative correlation between SD and r fm can also produce a positive association.
- This reversal depends on the direction of sex-specific selection, specifically whether it favors increased or decreased dimorphism.
- Genetic drift can generate non-zero SD even when selection pressures are identical between sexes.
Conclusions:
- The relationship between intersex genetic correlation and sexual dimorphism is more complex than previously assumed.
- A mechanistic framework is provided to explain the conditions influencing the correlation between r fm and SD.
- The findings offer a potential explanation for conflicting empirical results and highlight the role of genetic drift in generating sexual dimorphism.
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