The Mitochondrial Genome of the Screamer Louse Bothriometopus (Phthiraptera: Ischnocera): Effects of ExtensiveGene Rearrangements on the Evolution of the Genome

Mitochondrial (mt) genome rearrangement has generally been studied with respect to the phenomenon itself, focusing on their phylogenetic distribution and causal mechanisms. Rearrangements have additional significance through effects on substitution, transcription, and mRNA processing. Lice are an ideal group in which to study the interactions between rearrangements and these factors due to the heightened rearrangement rate within this group. The entire mt genome of the screamer louse Bothriometopus was sequenced and compared to previously sequenced louse genomes. The mt genome is 15,564 bp, circular, and all genes are encoded on the same strand. The gene arrangement differs radically from both other louse species and the ancestral insect. Nucleotide composition is A+T biased, but there is no skew which may be due to reversal of replication direction or a transcriptional effect. Bothriometopus has both tRNA duplication and concerted evolution which has not been observed previously. Eleven of the 13 protein-coding genes have 3' end stem-loop structures which may allow mRNA processing without flanking tRNAs and so facilitate gene rearrangements. There are five candidate control regions capable of forming stem-loop structures. Two are structurally more similar to the control regions of other insect species than those of other lice. Analyses of Bothriometopus demonstrate that louse mt genomes, in addition to being extensively rearranged, differ significantly from most insect species in nucleotide composition biases, tRNA evolution, protein-coding gene structures and putative signaling sites such as the control region. These may be either a cause or a consequence of gene rearrangements.