An unusual source of apparent mitochondrial heteroplasmy: duplicate mitochondrial control regions in Thalassarche albatrosses

Abstract

Molecular ecologists, in search of suitable molecular markers, frequently PCR-amplify regions of mitochondrial DNA from total DNA extracts. This approach, although common, is prone to the co-amplification of nuclear copies of transposed DNA sequences (numts), which can then generate apparent mitochondrial sequence heteroplasmy. In this study we describe the discovery of apparent mitochondrial sequence heteroplasmy in Thalassarche albatrosses but eliminate the possibility of true sequence heteroplasmy and numts and instead reveal the source of the apparent heteroplasmy to be a duplicated control region. The two control regions align easily but are not identical in sequence or in length. Comparisons of functionally significant conserved sequence blocks do not provide evidence of degeneration in either duplicate. Phylogenetic analyses of domain I of both control region copies in five Thalassarche species indicate that they are largely evolving in concert; however, a short section within them is clearly evolving independently. To our knowledge this is the first time contrasting evolutionary patterns have been reported for duplicate control regions. Available evidence suggests that this duplication may be taxonomically widespread, so the results presented here should be considered in future evolutionary studies targeting the control region of all Procellariiformes and potentially other closely related avian groups.