How can gene flow influence adaptation in sticklebacks?

How can gene flow influence adaptation in sticklebacks?

• A. Gene flow always speeds adaptation.
• B. Gene flow has no effect on adaptation.
• C. Gene flow can introduce maladaptive alleles or hinder local adaptation, but it can also spread beneficial alleles that aid adaptation.
• D. Gene flow only introduces deleterious mutations.

Answer: (D)

Gene flow is the movement of alleles among populations, so it can either help or hinder adaptation depending on the local environment and which alleles are being exchanged. In sticklebacks, populations in freshwater and marine settings face different predators, diets, and other stresses, which drive local adaptation in traits like armor plating and body form. If individuals from the marine population bring in alleles that favor heavy armor and those alleles are not advantageous in freshwater, gene flow can swamp the freshwater population’s adaptations and slow or prevent local adaptation. On the other hand, if migrating alleles happen to offer advantages in the freshwater environment—such as variants that improve survival under freshwater conditions or different armor configurations that work better there—gene flow can spread those beneficial alleles and accelerate adaptation. The net effect depends on how strong selection is locally, how much mixing occurs, and how often incoming alleles are advantageous in the local habitat.

Gene flow is the movement of alleles among populations, so it can either help or hinder adaptation depending on the local environment and which alleles are being exchanged. In sticklebacks, populations in freshwater and marine settings face different predators, diets, and other stresses, which drive local adaptation in traits like armor plating and body form. If individuals from the marine population bring in alleles that favor heavy armor and those alleles are not advantageous in freshwater, gene flow can swamp the freshwater population’s adaptations and slow or prevent local adaptation. On the other hand, if migrating alleles happen to offer advantages in the freshwater environment—such as variants that improve survival under freshwater conditions or different armor configurations that work better there—gene flow can spread those beneficial alleles and accelerate adaptation. The net effect depends on how strong selection is locally, how much mixing occurs, and how often incoming alleles are advantageous in the local habitat.