High prevalence of non-synonymous substitutions in mtDNA of cichlid fishes from Lake Victoria |
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Authors: | Kazumasa Shirai Nobuyuki Inomata Shinji Mizoiri Mitsuto Aibara Yohey Terai Norihiro Okada Hidenori Tachida |
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Institution: | 1. Graduate School of Systems Life Sciences, Kyushu University, Fukuoka, Japan;2. International College of Arts and Sciences, Fukuoka Women''s University, Fukuoka, Japan;3. Sekisui Chemical Tanzania Ltd., Dar es Salaam, Tanzania;4. Foundation for Advancement of International Science, Tsukuba, Japan;5. The Graduate University for Advanced Studies, Kanagawa, Japan;6. Department of Life Sciences, National Cheng Kung University, Tainan 701, Taiwan;g Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka, Japan |
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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. |
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Keywords: | LM Lake Malawi LT Lake Tanganyika LV Lake Victoria mtDNA mitochondrial DNA |
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