Blood-sucking lice are common. Genetically, they are also unusual, say Renfu Shao at the University of Queensland, Australia, and his colleagues. Using information from the Human Body Louse Genome Project, the team found that the mitochondrial genome of the human body louse (Pediculus humanus) is splintered into 18 mini-chromosomes.
Chromosome fragmentation seems to have evolved along with blood sucking: the authors found it in human head and pubic lice, as well as in blood-sucking lice of other primates, but not in related lice that feed on other material. The chromosomal break-up may have been advantageous by increasing recombination between mini-chromosomes and introducing genetic variation that helped lice adapt to a bloody mammalian diet.