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Species Concepts and Reproductive Isolating Barriers

Author(s): Tadzia GrandPré, PhD, Nancy Moreno, PhD, and Lisa Marie Meffert, PhD

Mechanical Isolation

Even if there are no temporal or behavioral cues to keep individuals of two species from hybridizing, it may simply be physically impossible for mating to take place. Mechanical isolation occurs when two species have significant anatomical differences that prevent them from mating.

For example, many species of the fly genus Drosophila are virtually indistinguishable except for differences in the male and female genitalia. Similar to the workings of a lock and key, males cannot copulate successfully with females from the wrong species. 

Mechanical isolation is a premating isolating barrier as well as a prezygotic isolating barrier.