Under which of the following conditions can we conclude that speciation has occurred in *Uta stansburiana*?

• A. Two populations of *Uta stansburiana* can no longer interbreed to produce fertile offspring.
• B. Two populations of *Uta stansburiana* occupy different habitats but still interbreed occasionally.
• C. Two populations of *Uta stansburiana* migrate at different times of the year but share the same gene pool.
• D. Two populations of *Uta stansburiana* show different coloration but have no reproductive barriers.

Answer: (A)

Verified step by step guidance

1. Understand the concept of speciation: Speciation occurs when populations of the same species become reproductively isolated, meaning they can no longer interbreed to produce fertile offspring. This is a key criterion for defining separate species under the biological species concept.
2. Analyze the first condition: If two populations of *Uta stansburiana* can no longer interbreed to produce fertile offspring, this indicates reproductive isolation, which is a definitive sign of speciation.
3. Evaluate the second condition: If two populations occupy different habitats but still interbreed occasionally, they are not reproductively isolated. Occasional interbreeding means they still share a gene pool, so speciation has not occurred.
4. Evaluate the third condition: If two populations migrate at different times of the year but share the same gene pool, this suggests temporal isolation might be developing. However, as long as they share a gene pool and can interbreed, speciation has not yet occurred.
5. Evaluate the fourth condition: If two populations show different coloration but have no reproductive barriers, this is an example of phenotypic variation within the same species. Without reproductive isolation, speciation has not occurred.