Fine-scale ecological segregation between plethodontid salamanders in replicated contact zones

Contact zones present unique opportunities to investigate ecological divergence, reproductive barriers, and gene flow between species. The two-lined salamander (Eurycea bislineata) species complex is a group of morphologically conserved taxa sharing a most recent common ancestor in the Miocene. Most species have allopatric distributions, and the phylogeographic history of the E. bislineata species complex suggests isolation and divergence in paleodrainage basins, with opportunities for secondary contact following drainage reorganize events. Here, we used RADcap data to investigate gene flow and ecological divergence in replicated contact zones between two species in the Appalachian foothills. Our results demonstrate that gene flow between these species is absent or rare, and larvae show strong, fine-scale ecological segregation among riffles, runs, and pools in streams. These results reinforce the conclusions of previous studies suggesting the evolutionary distinctiveness of these two species and underscore the importance of ecological factors in shaping local distributions.