Crocodylian Genomics: Unraveling Evolution, Development and Traditional Medicine.

Crocodylians have a long held a place in human mythology and history, with the first written record of crocodiles appearing as early as the 5^th century BC. Crocodiles and alligators have been farmed since the early 20^th century for tourism and, more recently, their skins and meat. Moreover, crocodile products are also valued in traditional medicine and several research groups are investigating the anti-microbial properties of crocodile sera. We report on an international effort to sequence three representative crocodilian species (Crocodylus porosus, Alligator mississippiensis and Gavialis gangeticus). We have produced a completed genome sequence for each species, predicted genes and proteins and provided preliminary gene names and predicted functions for these gene products. Alligator (the species with the best assembly and annotation) has 23,323 predicted genes, comparably with other vertebrate species. Phylogenetic analysis of crocodylian genes with other vertebrate genes identified 337 core gene families present in all vertebrates analyzed and 5,000 predicted genes were restricted to the three crocodylian species. Crocodylians have a slow rate of morphological and karyotype evolution. This slow rate of evolution is recapitulated at the nucleotide level. Moreover, our sequence data indicates that each of the three crocodilian species suffered a reduction in population size through the Pleistocene epoch. The slow rate of karyotypic and molecular evolution within the two extant orders of archosaurs has the potential to illuminate key features of the biology of their common ancestor, a subject of intense interest.