Can negative cytonuclear interactions explain mtDNA patterns in Bombina hybrid zones?

Recently we analyzed pattern of mtDNA variation across several transects finding no evidence for free mtDNA movement, but at the same time only a weak cytonuclear disequilibria between mtDNA haplotypes and unlinked diagnostic allozymes. To back these studies we made a large phylogeographic survey of mtDNA variation in both species, again finding no evidence of mtDNA introgression between the species. mtDNA of B.bombina and B.variegata appear highly divergent and K2P distance of ~9% suggests pre-Pleistocene split of the species and an independent history. We have obtained complete sequences of mtDNA from distinct phylogeographic groups to infer patterns of nonsynonymous substitutions and identified several non-conservative substitutions which may be targets for selection. Although direct evidence is lacking, large phenotypic, ecological and molecular divergence of these parapatric species make a strong argument for inferred negative epistatic effects underlying hybrid zone dynamics.