A beneficial allele is introduced into a bird subpopulation but fails to increase in frequency. What is likely preventing this increase?

The scenario describes a situation where a beneficial allele is introduced but does not increase in frequency within the bird subpopulation. Gene flow, which is the transfer of genetic material between populations, can play a critical role in the evolutionary dynamics of subpopulations.

When gene flow from other populations brings in alleles that are not beneficial in the specific local context, it can dilute the effect of beneficial alleles that have been introduced. In this case, if migrants from another population possess alleles that are more advantageous in the new environment, the advantageous allele may struggle to increase in frequency because the genetic contributions from these migrants can overwhelm the local adaptive potential of the beneficial allele.

Thus, it is the gene flow from migration that is likely preventing the beneficial allele from increasing in the subpopulation, as new individuals may carry alleles that are either neutral or disadvantageous, obstructing the local adaptation process. This highlights the importance of understanding the balance between local selection pressures and the effects of gene flow in shaping population genetics and evolutionary trajectories.