Incorporation of mitochondrial fragments in the nuclear genome (Numts) of the longhorned beetle Monochamus galloprovincialis (Coleoptera, Cerambycidae)

A mitochondrial DNA (mtDNA) study, based on 43 European populations (33 of them sampled in France) of Monochamus galloprovincialis , vector of the pinewood nematode, and 14 populations of its sister species Monochamus sutor was realized. Sequencing of 792 bp of the cytochrome oxidase I (COI) and 521 bp of the COII genes revealed numerous ambiguities on multiple nucleotide sites for half of M. galloprovincialis specimens studied (44.8%). Hypotheses of heteroplasmy and pseudogenes ( Numts ) were examined. The mtDNA isolation by alkaline lysis and cloning (for three successfully used individuals) both support the hypothesis that the ambiguous sequences amplified were not of mtDNA nature and validate the presence of Numts in the nuclear genome of M. galloprovincialis . Multiple copies of mtDNA-like sequences were found paralogous to COI, tRNA leucin and COII regions. Phenetic analysis placed different recently diverged mtDNA-like sequences as a close relative of mtDNA sequences, and grouped 10 closely related mtDNA-like sequences as a more basal clade, closer to ancestral states and to M. sutor . This result supports that this nuclear family of pseudogenes arose independently of the other events and may represent mitochondrial haplotypes sampled from M. galloprovincialis ancestral populations. This is the first time that Numts are proved for a longhorned beetle, whereas no Numts were found within its sister species M. sutor. The incorporation mechanism of Numts in unknown for M. galloprovincialis , however, excess of ambiguous sites corresponding to synonymous mutations placed on third codon position as well as the absence of Numts in M. sutor , conducted to the hypothesis of a recent transfer of these Numts in the nuclear genome of M. galloprovincialis .