Answer:3. Fusion
Explanation:Fusion is a term used to describe the bringing together or the joining of two cells,species etc in order to mix certain characteristics or features for the creation of a single New Cell or a Single specia. It also Describes the weakening of reproductive barriers, or blockages allowing the two populations to combine to form a new specie.
The interbreeding which took place between both species of salamander through the weakened barriers is known as FUSION.