Molecular studies on two variant repeat types of the common cetacean DNA satellite of the sperm whale, and the relationship between Physeteridae (sperm whales) and Ziphiidae (beaked whales)

In the sperm whale (Physeter macrocephalus) two different repeat types (A and B) of the common cetacean DNA satellite were identified. The evolution of each group of repeats appears to be independent from that of the other. The sequence similarity between the two groups is less than the similarity between group A and repeats of the satellite in related whale species. The systematic relationship within and between the families Physeteridae (sperm whales) and Ziphiidae (beaked whales) was addressed by both sequence analysis of the satellite and comparisons with the families Delphinidae and Phocoenidae. The mysticete blue whale (Balaenoptera musculus) was used as an outgroup in the comparisons. The molecular phylogeny, when maximum-parsimony analysis and the neighbor-joining method were used, grouped together species of each family. At the family level the ziphiids grouped closet to the families Phocoenidae and Delphinidae. The similarities between the common cetacean satellite of the blue whale and the sperm whale were greater than those between the blue whale and the other odontocetes included, suggesting that the evolution of the satellite is slower in the sperm whale than in the other odontocetes.