title: High prevalence of non-synonymous substitutions in mtDNA of cichlid fishes from Lake Victoria.
abstract: When a population size is reduced, genetic drift may fix slightly deleterious mutations, and an increase in nonsynonymous substitution is expected. It has been suggested that past aridity has seriously affected and decreased the populations of cichlid fishes in Lake Victoria, while geographical studies have shown that the water levels in Lake Tanganyika and Lake Malawi have remained fairly constant. The comparably stable environments in the latter two lakes might have kept the populations of cichlid fishes large enough to remove slightly deleterious mutations. The difference in the stability of cichlid fish population sizes between Lake Victoria and the Lakes Tanganyika and Malawi is expected to have caused differences in the nonsynonymous/synonymous ratio, ω (=dN/dS), of the evolutionary rate. Here, we estimated ω and compared it between the cichlids of the three lakes for 13 mitochondrial protein-coding genes using maximum likelihood methods. We found that the lineages of the cichlids in Lake Victoria had a significantly higher ω for several mitochondrial loci. Moreover, positive selection was indicated for several codons in the mtDNA of the Lake Victoria cichlid lineage. Our results indicate that both adaptive and slightly deleterious molecular evolution has taken place in the Lake Victoria cichlids' mtDNA genes, whose nonsynonymous sites are generally conserved.
authors.affiliation: Graduate School of Systems Life Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Shirai
authors.affiliation: International College of Arts and Sciences, Fukuoka Women's University, Fukuoka, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Inomata
authors.affiliation: Sekisui Chemical Tanzania Ltd., Dar es Salaam, Tanzania.
authors.forename: Shinji
authors.initials: S
authors.lastname: Mizoiri
authors.affiliation: Foundation for Advancement of International Science, Tsukuba, Japan.
authors.forename: Mitsuto
authors.initials: M
authors.lastname: Aibara
authors.affiliation: The Graduate University for Advanced Studies, Kanagawa, Japan.
authors.forename: Yohey
authors.initials: Y
authors.lastname: Terai
authors.affiliation: Foundation for Advancement of International Science, Tsukuba, Japan; Department of Life Sciences, National Cheng Kung University, Tainan 701, Taiwan.
authors.forename: Norihiro
authors.initials: N
authors.lastname: Okada
authors.affiliation: Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka, Japan. Electronic address: htachida@kyudai.jp.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Tachida
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D023681:Cichlids / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D029941:Fish Proteins / Q000235:genetics*; D005828:Genetics, Population; D060106:Lakes; D016013:Likelihood Functions; D009154:Mutation; D010802:Phylogeny
chemical_list: D004272:DNA, Mitochondrial; D029941:Fish Proteins
keywords: Adaptive substitution; Branch model; Branch-site model; Cichlids; Population size; Slightly deleterious mutation