Evolutionary dynamics of a mitochondrial rearrangement "hot spot" in the Hymenoptera

The arrangement of tRNA genes at the junction of the cytochrome oxidase II and ATPase 8 genes was examined across a broad range of Hymenoptera. Seven distinct arrangements of tRNA genes were identified among a group of wasps that have diverged over the last 180 Myr (suborder Apocrita); many of the rearrangements represent evolutionarily independent events. Approximately equal proportions of local rearrangements, inversions, and translocations were observed, in contrast to vertebrate mitochondria, in which local rearrangements predominate. Surprisingly, homoplasy was evident among certain types of rearrangement; a reversal of the plesiomorphic gene order has arisen on three separate occasions in the Insecta, while the tRNA(H) gene has been translocated to this locus on two separate occasions. Phylogenetic analysis indicates that this gene translocation is real and is not an artifactual translocation resulting from the duplication of a resident tRNA gene followed by mutation of the anticodon. The nature of the intergenic sequences surrounding this region does not indicate that it should be especially prone to rearrangement; it does not generally have the tandem or inverted repeats that might facilitate this plasticity. Intriguingly, these findings are consistent with the view that during the evolution of the Hymenoptera, rearrangements increased at the same time that the rate of point mutations and compositional bias also increased. This association may direct investigations into mitochondrial genome plasticity in other invertebrate lineages.