Final answer:
Gene flow is critical in allopatric speciation, acting as an evolutionary mechanism that is interrupted when populations are geographically separated. The lack of gene flow allows populations to evolve independently, potentially leading to speciation as a result of distinct mutations, natural selection, and genetic drift in isolated populations.
Step-by-step explanation:
The role that gene flow plays in allopatric speciation is quite significant. Allopatric speciation occurs when a population is divided by a geographic barrier, leading to the interruption of gene flow between the separated groups. When gene flow is disrupted, each group can evolve independently, with allele frequencies changing due to mutation, natural selection, and genetic drift. Over time, these changes can lead to the emergence of new species as populations become reproductively isolated from one another.
Isolation of populations is a critical first step in allopatric speciation. Natural barriers like rivers, lakes, or mountain ranges can prevent individuals from different populations from mating with each other. Without gene flow, populations may experience different mutations and selection pressures and begin to diverge genetically. This divergence can eventually lead to the development of reproductive barriers, as the populations evolve in response to their specific environments.
For example, if a population of rodents becomes divided by the formation of a new lake, gene flow is interrupted. Over time, the populations on either side of the lake may undergo distinctive evolutionary changes. These changes could range from physical adaptations to behavioral differences. If these groups remain isolated long enough, they may no longer be able to interbreed even if they come back into contact, having become distinct species through allopatric speciation.