Mitochondrial genome deletions and minicircles are common in lice (Insecta: Phthiraptera)
1 Discipline of Biogeosciences, Faculty of Science & Technology, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, Australia
2 Australian National Insect Collection & CSIRO Ecosystem Sciences, Black Mountain Laboratories, PO Box 1700, Canberra, ACT 2601, Australia
3 Systematic Entomology, Graduate School of Agriculture, Hokkaido University, Sapporo, 060-8589, Japan
4 Department of Biology, Brigham Young University, Provo, UT, 84602, USA
5 Illinois Natural History Survey, University of Illinois, 1816 South Oak St., Champaign, IL, 61820, USA
BMC Genomics 2011, 12:394 doi:10.1186/1471-2164-12-394Published: 4 August 2011
The gene composition, gene order and structure of the mitochondrial genome are remarkably stable across bilaterian animals. Lice (Insecta: Phthiraptera) are a major exception to this genomic stability in that the canonical single chromosome with 37 genes found in almost all other bilaterians has been lost in multiple lineages in favour of multiple, minicircular chromosomes with less than 37 genes on each chromosome.
Minicircular mt genomes are found in six of the ten louse species examined to date and three types of minicircles were identified: heteroplasmic minicircles which coexist with full sized mt genomes (type 1); multigene chromosomes with short, simple control regions, we infer that the genome consists of several such chromosomes (type 2); and multiple, single to three gene chromosomes with large, complex control regions (type 3). Mapping minicircle types onto a phylogenetic tree of lice fails to show a pattern of their occurrence consistent with an evolutionary series of minicircle types. Analysis of the nuclear-encoded, mitochondrially-targetted genes inferred from the body louse, Pediculus, suggests that the loss of mitochondrial single-stranded binding protein (mtSSB) may be responsible for the presence of minicircles in at least species with the most derived type 3 minicircles (Pediculus, Damalinia).
Minicircular mt genomes are common in lice and appear to have arisen multiple times within the group. Life history adaptive explanations which attribute minicircular mt genomes in lice to the adoption of blood-feeding in the Anoplura are not supported by this expanded data set as minicircles are found in multiple non-blood feeding louse groups but are not found in the blood-feeding genus Heterodoxus. In contrast, a mechanist explanation based on the loss of mtSSB suggests that minicircles may be selectively favoured due to the incapacity of the mt replisome to synthesize long replicative products without mtSSB and thus the loss of this gene lead to the formation of minicircles in lice.