What hypothesis did the researchers test in this study? what hypothesis did the researchers test in this study? reproductive isolation increases with geographic distance between dusky salamander populations. dusky salamanders are undergoing sympatric speciation. dusky salamanders are in the process of speciation?

This question is incomplete. The answer is b: 'Reproductive isolation increases with geographic distance between dusky salamander populations'. Reproduction isolation is important for speciation. Through different mechanisms, reproductive isolation prevents different species from mating, thereby preventing gene flow between species. Geographic distance is one such mechanism of isolating different species from each other. This would be an example of a pre-zygotic mechanism as it prevents mating.