Predicting the Evolution of Sexual Dimorphism in Gene Expression

Area of Science:

• Evolutionary biology
• Genomics
• Quantitative genetics

Background:

• Sexual dimorphism in gene expression is a key driver of phenotypic differences between sexes.
• Previous studies often assume dimorphism evolves solely due to direct selection acting differently on each sex.
• The influence of genetic covariance between traits and indirect selection on dimorphism has been largely overlooked.

Purpose of the Study:

• To investigate how relaxed assumptions about selection reveal new insights into the evolution of sexual dimorphism in gene expression.
• To analyze the role of the genetic-variance-covariance matrix (G) in shaping dimorphism.
• To re-evaluate gene expression data from Drosophila melanogaster considering indirect selection and genetic correlations.

Main Methods:

• Relaxed assumptions on selection to analyze the genetic-variance-covariance matrix (G).
• Reanalyzed gene expression data from Drosophila melanogaster.
• Estimated a G matrix for eight linear combinations of expression traits to account for measurement error.

Main Results:

• Gene expression dimorphism shows signatures of both direct and indirect selection.
• Sex-specific genetic variances were unequal, indicating sensitivity to selection.
• Analysis of the complete G matrix demonstrated that both sexually concordant and antagonistic selection can alter dimorphism.
• Indirect responses to selection via cross-trait covariances were substantial.

Conclusions:

• Sexual dimorphism in gene expression can evolve indirectly through various selection pressures, not solely direct sexual selection.
• The genetic architecture, particularly cross-trait covariances, plays a significant role in shaping dimorphism.
• The assumption that sexual dimorphism in transcription is always a direct adaptation may be incorrect in many instances.