Which of the following is a prezygotic reproductive isolation mechanism?

• A. Temporal isolation
• B. Hybrid inviability
• C. Hybrid sterility
• D. Zygote inviability after fertilization

Answer: (A)

Prezygotic reproductive isolation prevents mating or fertilization from happening in the first place. Temporal isolation fits here because species breed at different times, so even if they occupy the same area, they don’t mate together. This stops the formation of a zygote before fertilization can occur. The other options are postzygotic barriers that act after mating or fertilization: hybrid inviability means the hybrid zygote doesn’t develop, hybrid sterility means the hybrids survive but cannot reproduce, and zygote inviability after fertilization means fertilization occurs but the zygote fails to develop. So temporal isolation is the prezygotic mechanism.