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

• Published in: Molecular ecology 2014-06, Vol.23 (11), p.2811-2824
• Main Authors: Denton, Robert D, Kenyon, Laura J, Greenwald, Katherine R, Gibbs, H.Lisle
• Format: Article
• Language: English
• Subjects: Ambystoma; Ambystoma - classification; Ambystoma - genetics; Ambystoma barbouri; Ambystoma talpoideum; Animals; Bayes Theorem; Caudata; Cell Nucleus - genetics; DNA, Mitochondrial - genetics; environmental factors; Evolution, Molecular; Evolutionary biology; Gene Flow; Genetic markers; genetic variation; Haplotypes; introgression; Mitochondrial DNA; mitonuclear discordance; mole salamanders; Molecular Sequence Data; nuclear DNA; Ohio; Phylogeny; Reptiles & amphibians; Sequence Analysis, DNA
• ISSN: 0962-1083; 1365-294X
• DOI: 10.1111/mec.12775

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 analyse 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 within the range of A. texanum. We test three hypotheses for this discordance (undetected range expansion, mtDNA introgression, and hybridization) using nuDNA and mtDNA data analysed with methods that varied in the parameters estimated and the timescales measured. Results from a Bayesian clustering technique (structure), bidirectional estimates of gene flow (migrate‐n and IMa2) and phylogeny‐based methods (*beast, bucky) all support the conclusion that the discordance is due to geographically restricted mtDNA introgression from A. barbouri into A. texanum. Limited data on species‐specific tooth morphology match this conclusion. Significant differences in environmental conditions exist between sites where A. texanum with and without A. barbouri‐like mtDNA occur, suggesting a possible role for selection in the process of introgression. Overall, our study provides a general example of the value of using complimentary analyses to make inferences of the directionality, timescale, and source of mtDNA introgression in animals.