Hammerhead Sharks (Family Sphyrnidae)
Our research focuses on inferring the evolution of the unique head, referred to as a cephalofoil. In particular, we are using a phylogenetic framework to test alternative hypotheses about head shape evolution. This work is a collaborative effort funded by the National Science Foundation: Motta, P, S. Kajuira, and A. P. Martin. National Science Foundation Collaborative Research Proposal, "Functional Morphology, Sensory Physiology and Evolution of the Cephalofoil". In addition, we are interested in the phylogeography of widespread species.
Recent discoveries
The Evolution of the Cephalofoil
The first phylogenetic study of hammerheads was based on relatively short fragments of mtDNA. Although the results of the study were published (Martin, A. 1993. Hammerhead shark origins. Nature 364: 494), the data were not available on GenBank; however, the data are available here.
A more exhaustive phylogenetic of the group was accomplished by Doug Lim, and undergraduate student in my lab. Doug sequenced 4 mitochondrial genes and 3 nuclear genes and used a combination of Bayesian and likelihood methods to show that all previously published hypotheses for the group can be refuted in favor of a new hypothesis. This work will be submitted for publication soon.
Population Genetics of Widespread Species
Using mtDNA sequences from individuals collected across the globe, we showed that there is strong trans-oceanic genetic structure but little or not genetic structure along continental shelves. Our study suggests that although hammerheads are widely distributed, individuals do not undergone long-distance movement across ocean basins, although rare trans-oceanic dispersal occurs. For more information, see Duncan, K. M., A. P. Martin, B. Bowen, G. DeCouet. 2006. Global phylogeography and population structure in the scalloped hammerhead shark (Sphyrna lewini). Molecular Ecology 15L 2239-2251.
Links
There are several groups with an active interest in hammerhead sharks.