What process results from geographically isolating *Cirrhilabrus* populations due to fluctuating sea levels?

Allopatric speciation

When the lowering of sea levels during ice ages created barriers—such as dry land or water too deep for the reef-dwelling *Cirrhilabrus* to cross—it separated populations that previously shared gene flow. These isolated groups, situated on different reef patches or continental shelves, were forced to evolve independently. Over multiple cycles of the seas rising and falling, these separate populations developed reproductive isolation from each other. This classic pattern of speciation, where geographic separation is the primary mechanism leading to the formation of distinct species, is known specifically as allopatric speciation. The genetic differences, including color variations, established during this isolation persist even if the populations later reunite.