A gene with major phenotypic effects as a target for selection vs. homogenizing gene flow

Area of Science:

• Evolutionary biology
• Population genetics

Background:

• The Ectodysplasin (Eda) gene controls lateral plate number in three-spined stickleback, a model for parallel evolution.
• Freshwater stickleback populations repeatedly evolved reduced plating from marine ancestors, but many remain polymorphic.

Purpose of the Study:

• Investigate the role of Eda gene allele frequencies in adaptive divergence across polymorphic stickleback populations.
• Determine if selection or gene flow best explains variation in lateral plate number.

Main Methods:

• Tracked Eda allele frequency changes across seasons in 15 polymorphic populations.
• Compared Eda genotypes for body size and reproductive investment.
• Conducted a meta-analysis of selection signatures at the Eda gene.

Main Results:

• Observed fitness advantages for different Eda alleles in freshwater and brackish environments.
• Found poor correlation between Eda gene differentiation and habitat characteristics.
• Neutral population structure, not habitat, predicted lateral plate variation, indicating significant gene flow.

Conclusions:

• A balance between divergent selection and gene flow maintains lateral plate polymorphism in stickleback.
• Ecologically important genes may not always strongly contribute to local adaptation despite selection.