The Isthmus of Panama cut off gene flow between Atlantic and Pacific populations of a species of fish. The cessation of gene flow led to the accumulation of genetic differences between the populations, which led to reproductive isolation. Now Atlantic and Pacific populations of this fish are separate species that cannot interbreed, even if they were again to come into contact with each other. The process described is that of

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The description matches that of allopatric speciation, which occurs when a physical barrier (in this case, the Isthmus of Panama) separates a population and prevents gene flow. Over time, genetic differences can accumulate, leading to reproductive isolation and the development of separate species. The fact that the two populations cannot interbreed even if they were to come into contact again is a key feature of allopatric speciation.

The Isthmus of Panama Cut Off Gene Flow Between Atlantic