Phylogenetic analyses in cetacean species of the family Delphinidae using a short wavelength sensitive opsin gene sequence

The short wavelength sensitive (SWS) opsin gene is expected to contain informative sites for understanding the speciation of the family Delphinidae, because it is not functional in cetaceans. We determined partial SWS gene sequences from 15 delphinid species of 12 genera and from harbor porpoise for comparison. We found a 39-bp insertion that was shared by six species (the insertion group: Delphinus delphis, Delphinus capensis, Stenella longirostris, Stenella coeruleoalba, Lagenodelphis hosei, and Sousa chinensis) and common base substitutions shared by eight species (Stenella frontalis, Tursiops truncatus, and six species of the insertion group). As these insertions and substitutions are not found in the other seven delphinids or in the cloven-hoofed mammals (which are close to cetaceans), it is suggested that these eight species are more closely related to each other than to the other species. This hypothesis is supported by phylogenetic analyses. The eight species with the substitutions formed a clade containing two sister clades, one consisting of the insertion group and the other consisting of the two other species, in both neighbor-joining and Bayes analyses. Phylogenetic analyses also showed that Lissodelphis borealis and Lagenorhynchus obliquidens are closely related and that their common ancestor diverged from the others at an early stage of delphinid evolution.