Evolution of extensively fragmented mitochondrial genomes in the lice of humans

Bilateral animals are featured by an extremely compactmitochondrial (mt) genomewith 37 genes on a single circular chromosome. The human body louse, Pediculus humanus, however, has itsmt genes on 20 minichromosomes.Wesequenced the mt genomes of two otherhumanlice: the head louse, P. capitis, and the pubic louse, Pthirus pubis.Comparison amongthe threehumanlice revealed the presence of fragmentedmt genomes in theirmost recent common ancestor, which lived∼7Ma. The head louse has exactly the same set of mt minichromosomes as the body louse, indicating that the number of minichromosomes, and the gene content and gene arrangement in eachminichromosome have remained unchanged since the body louse evolved from the head louse∼107,000 years ago. The pubic louse has the same pattern of one protein-coding or rRNA gene perminichromosome(except one minichromosome with two protein-coding genes, atp6 and atp8) as the head louse and the body louse. This pattern is apparently ancestral to all human lice and has been stable for at least 7 Myr. Most tRNA genes of the pubic louse, however, are on different minichromosomes whencompared with their counterparts in the head louse and the body louse. It is evident that rearrangement of four tRNA genes (for leucine, arginine and glycine) was due to gene-identity switch by point mutation at the third anticodon position or by homologous recombination, whereas rearrangement ofother tRNAgeneswas bygene translocation betweenminichromosomes, likely causedby minichromosome split via gene degeneration and deletion