9707145 Naylor Galeomorph sharks are the most taxonomically-diverse and dominant group of living sharks, and include many of the large and well known species such as the great white, tiger, hammerhead, and whale sharks. The galeomorphs have an extensive fossil record that extends to the Jurassic, demonstrating that sharks represent an early offshoot in the vertebrate genealogical tree. In this research, Gavin Naylor of Iowa State University will employ DNA sequences acquired from both the mitochondrial and nuclear genomes to study phylogenetic relationships among well over 100 species of sharks, including representatives of seven different orders. Naylor will test whether each of the four orders of galeomorph sharks were derived from a common ancestor, and also will examine relationships among species in several lineages within each galeomorph order. The phylogenetic hypothesis will be used (i) in conjunction with the rich galeomorph fossil record to assess the time or origin of many morphological adaptations unique to sharks, and (ii) as a framework for interpreting the rich, existing database on shark parasite diversity. Naylor also will investigate the extent to which DNA sequence form different genes and from different regions of the same gene converge on the same genealogical tree. This analysis will provide information as to how DNA changes over time and how estimation of genealogical trees from DNA sequence data can be improved.
