Biology

The correct answer is: D.Postzygotic isolation exists between the two frog species.

Explanation:

The key detail here is that while hybrids between Rana lessonae and Rana ridibunda are formed, they are rarely successful in producing offspring when they mate among themselves. This indicates a postzygotic isolation mechanism, which happens after fertilization. In postzygotic isolation, the hybrid offspring may be inviable (they don't survive) or sterile (they cannot reproduce). In this case, the hybrids are likely viable but have reduced fertility, as evidenced by the inability to produce successful offspring when they mate with each other.

1.Postzygotic isolation refers to barriers that affect the viability or fertility of offspr...