Bony Vertebrate Evolution: Elephant Sharks Closer To Humans Than Teleost Fish
Survey sequencing of its genome identified four Hox clusters, suggesting that, unlike for teleost fishes, no additional whole-genome duplication has occurred.
They are also an important outgroup for understanding the evolution of bony vertebrates such as human and teleost fishes.
In a new study published online this week in the open access journal PLoS Biology, Byrappa Venkatesh, Sydney Brenner, and colleagues performed survey sequencing (1.4× coverage) of a chimaera, the elephant shark (Callorhinchus milii).
The elephant shark genome, estimated to be about 910 Mb long, comprises about 28% repetitive elements.
Comparative analysis of approximately 15,000 elephant shark gene fragments revealed examples of several ancient genes that have been lost differentially during the evolution of human and teleost fish lineages.
Interestingly, the human and elephant shark genomes exhibit a higher degree of synteny and sequence conservation than human and teleost fish (zebrafish and fugu) genomes, even though humans are more closely related to teleost fishes than to the elephant shark.
Unlike teleost fish genomes, the elephant shark genome does not seem to have experienced an additional round of whole-genome duplication.
These findings underscore the importance of the elephant shark as a useful “model” cartilaginous fish genome for understanding vertebrate genome evolution.
Citation: Venkatesh B, Kirkness EF, Loh YH, Halpern AL, Lee AP, et al. (2007) Survey sequencing and comparative analysis of the elephant shark (Callorhinchus milii) genome.
PLoS Biol 5(4): e101. doi:10.1371/journal.pbio.0050101. (http://www.plosbiology.org)
Note: This story has been adapted from a news release issued by Public Library of Science.
The elephant shark (Callorhinchus milii) is an uncommon animal model. Known by several names, such as ghost shark, elephant fish and silver trumpeter, the species is found in waters off southern Australia. The smooth-skinned fish grow to a maximum size of four feet and pose no threat to humans. Their distinctive hoe-shaped, proboscis-like snout is used to detect prey, primarily shellfish and bottom-dwelling invertebrates, through movement and weak electrical fields: here.