What is a common outcome of allopatric speciation if gene flow is restored?

In allopatric speciation, populations of a species become geographically isolated, which leads to genetic divergence due to different environmental pressures, mutations, and natural selection in their respective habitats. If gene flow is restored between these once-isolated populations, a common outcome can lead to the formation of sympatric populations.

Sympatric populations occur when two or more populations exist in the same geographic area and can interbreed. The reintroduction of gene flow can result in hybridization, where individuals from the two distinct populations reproduce, potentially leading to the sharing of genetic material and the formation of new genetic combinations. This can increase genetic diversity within the populations and may also lead to changes in traits that could further influence how these populations interact within the same ecological space.

While hybrid species can form as a result of interbreeding, it does not necessarily mean that a completely new species will arise every time gene flow is restored, as some populations may remain distinct despite the possibility of mating. Thus, the emergence of sympatric populations best describes the scenario where restored gene flow leads to coexistence and interaction between populations that had been previously isolated.