Directional epistasis is common in morphological divergence.

Area of Science:

• Evolutionary biology
• Genetics

Background:

• Epistasis, the interaction between genes, is often considered minor in evolution.
• Systematic directional epistasis, however, can significantly influence evolutionary trajectories by altering gene effects and evolvability.

Purpose of the Study:

• To empirically assess the prevalence and magnitude of directional epistasis across diverse traits and species.
• To investigate how directional epistasis affects additive genetic variance (evolvability) during evolution.

Main Methods:

• Development of a novel framework to estimate systematic epistasis patterns from line-cross experiments.
• Quantification of epistatic effects on 197 size-related traits in 24 animal and 17 plant species.

Main Results:

• Directional epistasis is prevalent across a wide range of traits and species.
• The strength of directional epistasis increases with greater morphological divergence between populations.
• In animals, a common pattern of negative directionality was observed for traits related to size, suggesting constraints on evolvability towards larger sizes.

Conclusions:

• Directional epistasis plays a substantial role in shaping evolutionary dynamics and can impose constraints on trait evolution.
• The findings challenge the notion of epistasis being unimportant and highlight its significance in understanding evolutionary processes.