Mitochondrial genome sequences of representatives of three families of scorpionflies (Order Mecoptera) and evolution in a major duplication of coding sequence

Abstract

The complete mitochondrial DNA sequences of a hangingfly, Bittacus pilicornis (Mecoptera: Bittacidae), a snow scorpion fly, Boreus elegans (Mecoptera: Boreidae), and a nearly complete sequence from another scorpionfly species, Microchorista philpotti (Mecoptera: Nannochoristidae) were determined. The coding sequence of all three genomes includes the 37 genes normally found in insect mtDNAs, in the same gene order as first described in Drosophila. In addition to the standard set of genes, the Microchorista sequence includes a large duplication of the coding region. The duplication is at least 4 kb (and may be much larger) and includes the remnants of three protein-coding genes and seven tRNA genes. The duplication evidently arose as a single event, and the duplicated region can be aligned in its entirety with the corresponding region of the functional genome. Although most of the genes contain defects that render them nonfunctional, analysis shows that the protein-coding genes in the duplicated region evolved for a considerable period under constraints expected of functional protein-coding genes. It is evident, therefore, that for a period two copies of some of the mitochondrial genes were functional in this species, including genes coding for proteins.