The sequence arrangement of mitochondrial genes is highly conserved in metazoans. Exceptionally, the sequence arrangement of genes in the ring mitochondrial DNA strand of hard ticks underwent at least three segment transpositions after diverging from the prostriate ancestor. The shuffle in the arrangement was driven or at least permitted by the duplication of the transcriptional control region in the ancestral lineage. Following its duplication the CR2 was transposed to a new neighbor, the tRNA-Leucine. The second translocation moved this short segment, CR2+tRNA-Leucine to the other side of NAD1. The third translocation involved the repositioning of an 8 gene segment from NAD1-CR1 to a new site between NAD3 and NAD5. This last arrangement is found in all Metastriate ticks sequenced except the genus Africaniella. The arrangment in Africaniella is derived from step 2 in the sequence and thus resolves this unique Old World genus as an early branch from the proto-Metastriate stem, which is supported by the branching sequence found in the COXI based phylogeny. These lineages are also aligned as haplotypes of the nuclear 18S ribosomal gene. The duplication of the CR originated in the austral clade of the prostriate ticks. The step 1 transposition of CR2 from a tandem repeat to neighbor tRNA-Leucine is synaopomorphic for the austral clade of Ixodes and all Metastriates.
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