title: Comparative analysis of complete mitochondrial genomes suggests that relaxed purifying selection is driving high nonsynonymous evolutionary rate of the NADH2 gene in whitefish (Coregonus ssp.).
abstract: Several studies have recently reported evidence for positive selection acting on the mitochondrial genome (mitogenome), emphasizing its potential role in adaptive divergence and speciation. In this study we searched 107 full mitogenomes of recently diverged species and lineages of whitefish (Coregonus ssp.) for signals of positive selection. These salmonids show several distinct morphological and ecological differences that may be associated with energetics and therefore potentially positive selection at the mitogenome level. We found that purifying selection and genetic drift were the predominant evolutionary forces acting on the analyzed mitogenomes. However, the NADH dehydrogenase 2 gene (ND2) showed a highly elevated dN/dS ratio compared to the other mitochondrial genes, which was significantly higher in whitefish compared to other salmonids. We therefore further examined nonsynonymous evolution in ND2 by (i) mapping amino acid changes to a protein model structure which showed that they were located away from key functional residues of the protein, (ii) locating them in the sequences of other species of fish (Salmonidae, Anguillidae, Scombridae and Percidae) only to find pronounced overlap of nonsynonymous regions. We thus conclude that relaxed purifying selection is driving the evolution of ND2 by affecting mostly regions that have lower functional relevance.
authors.affiliation: Department of Bioscience, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark. Electronic address: magnus.jacobsen@bios.au.dk.
authors.forename: Magnus W
authors.initials: MW
authors.lastname: Jacobsen
authors.affiliation: Department of Bioinformatics and RNA Biology, University of Copenhagen, Ole Maaløesvej 5, 2200 København N, Denmark.
authors.forename: Rute R
authors.initials: RR
authors.lastname: da Fonseca
authors.affiliation: Département de Biologie, Institut de Biologie Intégrative et des Systèmes (IBIS), Pavillon Charles-Eugène-Marchand, 1030, Avenue de la Médecine, Université Laval, Québec, Québec, Canada G1V 0A6.
authors.forename: Louis
authors.initials: L
authors.lastname: Bernatchez
authors.affiliation: Department of Bioscience, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Hansen
mesh_terms: D000818:Animals; D004463:Ecology; D019143:Evolution, Molecular; D050259:Genes, Mitochondrial; D040961:Genetic Drift; D054629:Genome, Mitochondrial; D059645:Mutation Rate; D009245:NADH Dehydrogenase / Q000235:genetics*; D010802:Phylogeny; D020641:Polymorphism, Single Nucleotide; D012487:Salmonidae / Q000145:classification / Q000235:genetics*; D012641:Selection, Genetic
chemical_list: D009245:NADH Dehydrogenase
keywords: Coregonus ssp.; Mitogenome; ND2; Positive selection; Relaxed purifying selection; dN/dS