Which of the following is an example of a prezygotic isolating mechanism?

Behavioral isolation is a prezygotic isolating mechanism because it prevents mating between different species by differences in their mating behaviors or rituals. For instance, if two species have distinct mating calls or specific courtship behaviors, individuals from one species may not recognize or be attracted to the mating signals of another species. This isolation occurs before fertilization can take place, thereby preventing the formation of hybrids.

In contrast, the other options describe postzygotic isolating mechanisms. Hybrid viability refers to the ability of hybrid offspring to develop and survive to maturity, while hybrid sterility refers to the inability of hybrids to reproduce, such as mules, which are sterile offspring of horses and donkeys. Developmental isolation, while it may seem like a prezygotic mechanism, typically involves genetic differences that manifest after fertilization has occurred, affecting the viability of the developing embryo. Thus, these mechanisms occur after mating has taken place, making them postzygotic rather than prezygotic.