Final answer:
Pairs of closely related species that emerge due to geographic isolation, like the snapping shrimp on either side of the isthmus of Panama, are known as sister species.
Step-by-step explanation:
When snapping shrimp were separated by the formation of the isthmus of Panama, closely related species developed on either side of the isthmus. These pairs of species are known as sister species. Sister species are pairs of related species that have emerged due to geographic isolation but still retain a clear relationship to one another because of their common ancestry. This type of speciation often results from a physical barrier, such as the isthmus, which prevents gene flow between populations, leading to reproductive isolation and eventually, the emergence of new species.