Percent identity and phylogenetic relationships of Caspian Sea sturgeon species based on mitochondrial genome sequences

Mitochondrial genome is an ideal model to study evolution and phylogenetic relationships. In this study, complete mitochondrial genomes of six species of Caspian sea sturgeon including Persian sturgeon, Russian sturgeon, Ship sturgeon, Sterlet sturgeon, Starry sturgeon and Beluga sturgeon along with separate nucleotide and amino acid sequences of 13 PCGs per each genome including ND1, ND2, ND3, ND4, ND5, ND6, ATP6, ATP8, COX1, COX2, COX3, ND4L and CYTB were retrieved from NCBI database and compared. The results obtained from sequence distance analysis by DNAStar software based on complete mitochondrion genome showed high genetic similarity (99 %) between Persian and Russian sturgeon. Also, the lowest similarity (95 %) was observed between Sterlet and Starry sturgeon. In phylogenetic analysis by MEGA7 software, two main clusters with two sub-clusters for one of the main clusters were identified. Persian and Russian sturgeon species were grouped in first sub-cluster, Ship and Sterlet species fall in the other sub-cluster and Starry sturgeon with Beluga formed a different distinct cluster. The results obtained from the comparison of the 13 PCGs sequences were similar to the sequences of the complete mitochondrial genomes. The most difference in nucleotide sequences were observed in CYTB, ATP6, ND2, ND5 and ND6 genes and the lowest difference for ND4L gene. The results obtained from the comparison of the 13 genes amino acid sequences were different as the order of the species was changed and 100 % genetic similarity were observed for some genes such as COX3 and ND4L genes. Based on the results of the present study, mitochondrial genome sequences could be used for phylogenetic analysis and clustering of different species of sturgeons. However, the accuracy of investigations by complete mitochondrial genomes is higher than the nucleotide sequences of the genes, and using the amino acid sequences is not suggested due to their codon nature.