Large geographic range size reflects a patchwork of divergent lineages in the long-toed salamander (Ambystoma macrodactylum).

For northern taxa, persistence in multiple vs. single Pleistocene refugia may have been an important determinant of contemporary range size, with larger ranges achieved by species that colonized the north from several glacial refugia. Under this hypothesis, widespread species are expected to demonstrate marked phylogeographic structure in previously glaciated regions. We use a genome-wide survey to characterize genetic structure and evaluate this hypothesis in the most widely distributed salamander in the Pacific Northwest, the long-toed salamander (Ambystoma macrodactylum). Patterns of variation based on 751 amplified fragment length polymorphism (AFLP) loci and mitochondrial sequence data were concordant and support the recognition of at least four distinct lineages of long-toed salamander. The distributions of these lineages indicate that multiple refugia contributed to the species' large contemporary range. At the same time, with up to 133 AFLP bands differing between lineages and levels of sequence divergence ranging from 2.5 to 5.8%, these lineages would be considered separate species by some definitions. Such splitting would partition the large geographic range of the long-toed salamander into several relatively restricted ranges. Our results thus also underscore the potential for estimates of geographic range size to vary considerably depending on the taxonomic treatment of cryptic lineages.