Oral Presentation Society for Molecular Biology and Evolution Conference 2016

Resolving the Phylogenetic Position of Coelacanth: The Closest Relative Is Not Always the Most Appropriate Outgroup (#32)

Naoko Takezaki 1 , Hidenori Nishihara 2
  1. Kagawa University, Kitagun, KAGAWA, Japan
  2. Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan

Determining the phylogenetic relationship of two extant lineages of lobe-finned fish, coelacanths and lungfishes, and tetrapods is important for understanding the origin of tetrapods. We analyzed datasets from two previous studies along with a newly collected dataset, each of which had varying numbers of species and genes and varying extent of missing sites. We found that in all the datasets the sister relationship of lungfish and tetrapods was constructed with the use of cartilaginous fish as the outgroup with a high degree of statistical support. In contrast, when ray-finned fish were used as the outgroup, which is taxonomically an immediate outgroup of lobe-finned fish and tetrapods, the sister relationship of coelacanth and tetrapods was supported most strongly, although the statistical support was weaker. Even though it is generally accepted that the closest relative is an appropriate outgroup, our analysis suggested that the large divergence of the ray-finned fish as indicated by their long branch lengths and different amino acid frequencies made them less suitable as an outgroup than cartilaginous fish.