Author(s)

Kenji Sorimachi, Teiji Okayasu, Shuji Ohhira, Nobuhide Masawa, Ichio Fukasawa

Center of Medical Informatics, Dokkyo Medical University, Tochigi, Japan.
Department of Anatomic Diagnostic Pathology, Dokkyo Medical University, Tochigi, Japan.
Department of Obstetrics and Gynecology, Dokkyo Medical University, Tochigi, Japan;.
Laboratory for International Environmental Health, Dokkyo Medical University, Tochigi, Japan.

Cluster analyses using the amino acid content predicted from the coding regions (13 genes) of complete vertebrate mitochondrial genomes as traits grouped selected vertebrates into two clusters, terrestrial and aquatic vertebrates. Exceptions were the hagfish (Eptatretus burgeri), thought to be an early ancestor of vertebrates, and the black spotted frog (Rana nigromaculata), which is terrestrial as an adult and aquatic as a larva. These two species fall into the terrestrial and aquatic clusters, respectively. Using the nucleotide (G, C, T and A) content in the coding and non-coding regions, and in the complete genome as traits, similar results were obtained but with some additional exceptions. In addition, phylogenetic analyses of 16S rRNA sequences produced a consistent result. The results of this study indicated that vertebrate evolution is controlled by natural selection under both an internal bias as a result of nucleotide replacement genomic rules, and an external bias caused by environmental biospheric conditions.

Natural Selection; Vertebrate Evolution; Complete Mitochondrial Genome; Amino Acid Composition; 16S rRNA; Hagfish (Eptatretus burgeri)

Sorimachi, K. , Okayasu, T. , Ohhira, S. , Masawa, N. and Fukasawa, I. (2013) Natural selection in vertebrate evolution under genomic and biosphere biases based on amino acid content: Primitive vertebrate hagfish (Eptatretus burgeri). Natural Science, 5, 221-227. doi: 10.4236/ns.2013.52033.