What hypothesis did the researchers test in this study?

A. Reproductive isolation increases with geographic distance between dusky salamander populations.

B. Dusky salamanders are in the process of speciation.

C. Dusky salamanders are undergoing sympatric speciation.

A. Reproductive isolation increases with geographic distance between dusky salamander populations.

Explanation:

The researchers tested the reproductive isolation of pairs of salamander population by leaving one male and one female together and later check the females for the presence of sperm. They think that when populations become geographically isolated, preventing mating between individuals in different populations and thus stopping gene flow. They studied different populations on different mountains.