Abstract

Fragmented mitochondrial (mt) genomes have been reported in 11 species/subspecies of sucking lice (suborder Anoplura) that infest humans, chimpanzees, pigs, horses and rodents. There is substantial variation among these lice in mt karyotype: the number of minichromosomes of a species/subspecies ranges from 9 to 20; the number of genes in a minichromosome ranges from 1 to 8; gene arrangement in a minichromosome differs between species, even in the same genus. We sequenced the mt genome of the guanaco louse, Microthoracius praelongiceps, to help establish the ancestral mt karyotype for sucking lice and understand how fragmented mt genomes evolved. The guanaco louse has 12 mt minichromosomes; each minichromosome has 2–5 genes and a non-coding region. The guanaco louse shares many features with rodent lice in mt karyotype, more than with other sucking lice. The guanaco louse, however, is more closely related phylogenetically to human lice, chimpanzee lice, pig lice and horse lice than to rodent lice. By analysis of shared features in mt karyotype, we infer that the most recent common ancestor of sucking lice, which lived ~75 MYA , had 11 minichromosomes; each minichromosome had 1–6 genes and a non-coding region. As sucking lice diverged, splitting of mt minichromosomes occurred many times in the lineages leading to the lice of humans, chimpanzees and rodents whereas merging of minichromosomes occurred in the lineage leading to the lice of pigs and horses. Together, splits and mergers of minichromosomes created the most complex and dynamic mt genome organization seen in animals.