Biogeography of the southeastern United States: A comparison of salamanderphylogeographic studies

Most phylogeographic studies of species from the southeastern United States have shown a simple east-west division of mtDNA variation. However, a stud y of the salamander Ambystoma maculatum resulted in a more complex pattern that includes a close affinity between populations from the Central Highlan ds of Missouri and Arkansas and the Coastal Plain separated by a geneticall y distinct central group of populations. We test the generality of this obs ervation by surveying mitochondrial DNA (mtDNA) variation in the closely re lated species A. talpoideum. An Ambystoma-specific intergenic spacer was am plified and sequenced. The 26 resulting haplotypes varied from 380 to 800 b ase pairs, and alignments, including the outgroup, required 101 insertions/ deletions Sequence divergence among haplotypes ranged from 0.001 to 0.758. Population subdivision was extensive (theta = 0.64). Phylogenetic analysis of A. talpoideum mtDNA sequence reveals a close relationship between the po pulations from the Central Highlands and the Coastal Plain. This result is similar to that obtained for A. marulatum, although the A. talpoideum clade is not as well differentiated from its sister clades. We discuss the diffe rences and similarities between the two Ambystoma species and previous stud ies and call for increased focus on multiple species with similar ecologies as a way to detect subtle biogeographic events.