How does gene flow influence local adaptation in sticklebacks?

How does gene flow influence local adaptation in sticklebacks?

• A. Gene flow can prevent local adaptation entirely in all cases.
• B. Gene flow always acts to speed up adaptation.
• C. Gene flow has no effect on local adaptation.
• D. Gene flow can dilute locally adapted alleles, but strong selection can maintain adaptation; moderate gene flow may spread beneficial alleles between populations.

Answer: (D)

Gene flow moves alleles among populations, which can either erode or facilitate local adaptation depending on the balance with selection. In sticklebacks, when individuals migrate between marine and freshwater habitats, alleles favored in one environment can spread into the other and dilute the locally advantageous gene variants. If the local environment exerts strong selection for those locally adapted alleles, it can maintain the adaptation despite this influx. At the same time, a moderate level of gene flow can help spread beneficial alleles between populations, aiding adaptation without completely erasing differences. That combination—dilution by flow, maintained adaptation by strong selection, and potential spread of useful alleles when flow is moderate—best captures how gene flow influences local adaptation.

Gene flow moves alleles among populations, which can either erode or facilitate local adaptation depending on the balance with selection. In sticklebacks, when individuals migrate between marine and freshwater habitats, alleles favored in one environment can spread into the other and dilute the locally advantageous gene variants. If the local environment exerts strong selection for those locally adapted alleles, it can maintain the adaptation despite this influx. At the same time, a moderate level of gene flow can help spread beneficial alleles between populations, aiding adaptation without completely erasing differences. That combination—dilution by flow, maintained adaptation by strong selection, and potential spread of useful alleles when flow is moderate—best captures how gene flow influences local adaptation.