Which of the following is an example of a postzygotic reproductive barrier?
a. One Ceanothus shrub lives on acid soil, another on alkaline soil.
b. Mallard and pintail ducks mate at different times of year.
c. Two species of leopard frogs have different mating calls.
d. Hybrid offspring of two species of jimsonweeds always die before reproducing.

Verified step by step guidance

1. Step 1: Understand the concept of postzygotic reproductive barriers. These barriers occur after fertilization and prevent the resulting hybrid offspring from surviving, reproducing, or being viable.
2. Step 2: Analyze each option to determine if it describes a postzygotic barrier. For example, options a, b, and c describe prezygotic barriers, which prevent fertilization from occurring due to factors like habitat, timing, or behavioral differences.
3. Step 3: Focus on option d, which mentions hybrid offspring dying before reproducing. This is a clear example of a postzygotic barrier because it occurs after fertilization and affects the viability or reproductive success of the hybrid.
4. Step 4: Compare option d to the definition of postzygotic barriers to confirm that it fits the criteria. The death of hybrid offspring before reproduction prevents gene flow between the parent species.
5. Step 5: Conclude that option d is the correct example of a postzygotic reproductive barrier, as it directly involves the failure of hybrid offspring to survive or reproduce.

Key Concepts

Reproductive Barriers

Reproductive barriers are mechanisms that prevent species from interbreeding, thus maintaining species integrity. They can be classified into prezygotic barriers, which occur before fertilization, and postzygotic barriers, which occur after fertilization. Understanding these barriers is crucial for studying speciation and biodiversity.

Postzygotic Barriers

Postzygotic barriers are reproductive isolating mechanisms that occur after the formation of a zygote. These barriers can lead to hybrid inviability, where hybrid offspring do not survive to maturity, or hybrid sterility, where hybrids are unable to reproduce. An example is when hybrid offspring are inviable or die before reaching reproductive age.

Speciation

Speciation is the evolutionary process by which populations evolve to become distinct species. It often involves the development of reproductive barriers that prevent gene flow between populations. Understanding speciation is essential for grasping how biodiversity arises and is maintained in ecosystems.