Molecular phylogenetic relationship of Tetraodon pufferfish based on mitochondrial DNA analysis

Pufferfishes belonging to the genus Tetraodon form one of the largest groups in the family Tetraodontidae. This group consists of more than 20 species distributed across freshwater, as well as brackish and coastal waters, of Africa and Southeast Asia. However, their phylogenetic and evolutionary relationships are still ambiguous. In the present study, mitochondrial genes encoding 16S rRNA and cytochrome b were sequenced for 17 Tetraodon species collected from various areas mentioned above. Supermatrix analysis based on the complete sequences of the two genes from Tetraodon species was performed using a tree with 50 tetraodontid species (including 7 Tetraodon species) as a backbone. The obtained phylogenetic tree classified Tetraodon species into three groups, correlating well with their habitats, such as Asian freshwater, Asian brackish water, and African freshwater. We also showed that salinity tolerance of Asian freshwater species T. cochinchinensis was apparently lower than that of Asian brackish water species T. nigroviridis, suggesting that the speciation of Tetraodon species in the Asian freshwater group was caused by the molecular evolution associated with osmotic regulation.