Natural selection on a major armor gene in threespine stickleback

Area of Science:

• Evolutionary biology
• Genetics
• Ecology

Background:

• Adaptive evolution involves changes in gene frequencies driven by natural selection.
• The Ectodysplasin gene locus influences lateral plate development in threespine stickleback fish.
• A derived allele (low) reducing plate number repeatedly appears in freshwater stickleback populations that originated from marine ancestors.

Purpose of the Study:

• To experimentally estimate the effects of selection on the Ectodysplasin locus in threespine stickleback.
• To understand the genetic mechanisms of adaptation during colonization of freshwater environments.

Main Methods:

• Marine stickleback fish carrying both ancestral (complete) and derived (low) Ectodysplasin alleles were transplanted into freshwater ponds.
• Genotype frequencies were monitored over one generation to track changes in allele prevalence.

Main Results:

• The low allele, associated with reduced lateral plates, increased in frequency in the freshwater environment.
• This increase was observed after lateral plates developed, suggesting a fitness advantage, likely related to growth.
• Opposing selection pressures were noted at the larval stage, and fitness dominance varied throughout the fish's life.

Conclusions:

• The Ectodysplasin locus is under selection during freshwater adaptation in stickleback.
• Observed allele frequency changes suggest a growth advantage conferred by the low allele post-larval development.
• Complex selection patterns may indicate pleiotropy or selection on linked genetic loci.