Evolutionary basis of mitonuclear discordance between sister species of mole salamanders (Ambystoma sp.)

Distinct genetic markers should show similar patterns of differentiation between species reflecting their common evolutionary histories yet there are increasing examples of differences in the biogeographic distribution of species-specific nuclear (nuDNA) and mitochondrial DNA (mtDNA) variants within and between species. Identifying the evolutionary processes that underlie these anomalous patterns of genetic differentiation is an important goal. Here we analyze the putative mitonuclear discordance observed between sister species of mole salamanders (Ambystoma barbouri and A. texanum) in which A. barbouri-specific mtDNA is found in animals located in the range of A. texanum. We test three hypotheses for this discordance (undetected range expansion, mtDNA introgression and hybridization) using nuDNA and mtDNA data analyzed with methods that varied in the parameters estimated and the timescales measured. Results from a Bayesian clustering technique (structure), bi-directional estimates of g...