head & pubic lice split ~7 Ma?
- Genome Biol Evol 4(11):1088-1101 doi 10.1093/gbe/evs088 open access
Evolution of extensively fragmented mitochondrial genomes in the lice of
Shao R, Zhu XQ, Barker SC & Herd K 2012
Bilateral animals are featured by an extremely compact mitochondrial (mt)
genome with 37 genes on a single circular chromosome.
The human body louse Pediculus humanus, however, has its mt genes on 20
We sequenced the mt genomes of 2 other human lice:
- the head louse Pediculus capitis &
- the pubic louse Pthirus pubis.
Comparison among the 3 human lice revealed the presence of fragmented mt
genomes in their LCA ~7 Ma.
The head louse has exactly the same set of mt mini-chromosomes as the body
the number of mini-chromosomes & the gene content & gene arrangement in
each mini-chromosome have remained unchanged since the body louse evolved
from the head louse ~107 ka.
The pubic louse has the same pattern of one protein-coding or rRNA gene
per mini-chromosome (except 1 mini-chromosome with 2 protein-coding genes,
atp6 & atp8) as the head louse & the body louse.
This pattern is apparently ancestral to all human lice, and has been
stable for at least 7 Ma.
Most tRNA genes of the pubic louse, however, are on different
mini-chromosomes when compared with their counterparts in the head louse &
the body louse.
It is evident that re-arrangement of 4 tRNA genes (for leucine, arginine,
glycine) was due to gene-identity switch by point mutation at the 3d
anti-codon position or by homologous recombination ;
re-arrangement of other tRNA genes was by gene translocation between
mini-chromosomes, likely caused by mini-chromosome split via gene
degeneration & deletion.
This might suggest that the hominid LCA (Gorilla-Homo-Pan) ~7 Ma had head
separate hairs & pubic hairs, IOW, had a naked body.