A certain species of salamander was split into two populations by a wide, dry valley, and the populations began to diverge from each other. After a period of time, some members of the two populations began to interbreed in a hybrid zone at the southern end of the valley. Only weak reproductive barriers existed by this time, so the two populations could freely interbreed and re-establish gene flow. This outcome in a hybrid zone is known as .

The correct answer is: Fusion.

Explanation:

In the course of speciation in salamander the following events occurred:Two populations of a particular species of salamander got geographically isolated from each other by a dry valley.Each of the populations developed independently of each other according to the environment each of them were exposed to. This caused them to develop and accumulate mutations that made them genetically diverged from each other. Ultimately, a reproductive barrier was established between them, hence they lost the capability of interbreeding with each other and producing viable offspring.But, at the junction zone or hybrid zone (the region of the habitat where individuals of both the populations lived) the reproductive barrier was weak and reproduction by interbreeding, hence, gene flow was possible.In evolutionary science, this hybrid zone is referred to as the zone of Fusion.