River Drainage Reorganization and Reticulate Evolution in the Two-Lined Salamander (Eurycea bislineata) Species Complex.

This article focuses on the complex reticulate evolutionary history of the two-lined salamander (Eurycea bislineata) species complex in the eastern United States, highlighting how river drainage reorganization has influenced patterns of vicariance, dispersal, secondary contact, and introgression. Using genome-scale triple-enzyme restriction site-associated DNA sequencing (3RAD) data from over 100 individuals across major mitochondrial DNA (mtDNA) lineages, the study reveals discordance among morphological, mitochondrial, and nuclear datasets is best explained by hybridization and gene flow rather than a strictly bifurcating evolutionary tree. The findings emphasize that current taxonomy inadequately reflects species boundaries due to reticulate evolution, and future systematic revisions should incorporate genomic data, phenotypic reassessment, and focus on contact zones and reproductive isolation. Additionally, the study situates these evolutionary patterns within the dynamic and sometimes contentious paleodrainage history of the Appalachian region, underscoring the broader significance of accounting for introgression in phylogeographic and taxonomic research.