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

The arrangement of tRNA Penes 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 r earrangements represent evolutionarily independent events. Approximately eq ual proportions of local rearrangements, inversions, and translocations wer e observed, in contrast to vertebrate mitochondria, in which local rearrang ements 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 t ranslocated to this locus on two separate occasions. Phylogenetic analysis indicates that this gene translocation is real and is not an artifactual tr anslocation resulting from the duplication of a resident tRNA gene followed by mutation of the anticodon. The nature of the intergenic sequences surro unding this region does not indicate that it should be especially prone to rearrangement, it does not generally have the tandem or inverted repeats th at might facilitate this plasticity. Intriguingly, these findings are consi stent with the view that during the evolution of the Hymenoptera, rearrange ments increased at the same time that the rate of point mutations and compo sitional bias also increased. This association may direct investigations in to mitochondrial genome plasticity in other invertebrate lineages.