Many tree frog populations are threatened due to habitat loss. In an effort to promote conservation, tree frogs may be bred in captivity. A zoo acquired male and female tree frogs from two different populations. In the zoo, the tree frogs were able to successfully mate within their own population, but breeding attempts between the two populations were unsuccessful.
Based on this information, which statement correctly describes the relationship between the two populations of tree frogs?

A. They are in the same species but different kingdoms.

B. They are in the same class but different phyla.

C. They are in the same family but different orders.

D. They are in the same genus but different species.