Genetic Analysis of Great White Shark Reveals Surprises

The first large-scale exploration of the genetic code of the great white shark has revealed some unexpected insights into what makes the iconic apex predator so distinctive.

Researchers from Cornell University and Nova Southeastern University's Save Our Seas Shark Research Center published their surprise finds in the journal BMC Genomics.

Seeking genetic similarities and differences that might explain the characteristics of the white shark, the researchers compared the genetic makeup of the great white to that of zebrafish and human genes, focusing on the RNA sequences expressed by organism's genes (known as the transcriptome). Zebrafish are, genetically, one of the best understood fish, and human genes have long been a point of important research.

All three species have gene products common among them, so the researchers were able to focus on those and establish a common comparative base.

Although the researchers expected to the proportion of the white shark's gene products associated with metabolism to be greater than humans' or zebrafishes', it turns out there are fewer differences than they expected, which the researchers said was a surprise considering boney fish like the zebrafish are much more closely related to the white shark than humans.

Researchers were also surprised to find that the transcriptomes in the white shark's heart showed greater genetic similarity to humans than zebrafish.

The results raised more questions than provided answers.

"It's intriguing why there are these fewer differences in the proportion of gene products between white sharks and humans, than white sharks and zebrafish, when the complete opposite was expected based on evolutionary affinities," said study co-author Mahmood Shivji. "One possibility for the apparent greater similarity between white sharks and humans in the proportion of gene products associated with metabolism might be due partly to the fact that the white shark has a higher metabolism because it is not a true cold-blooded fish like bony fishes; however this explanation remains a hypothesis to be further tested."

White sharks, notably, are regionally warm-blooded, meaning parts of their body are kept at higher temperatures than the watery environment where it lives. This characteristically associated the white shark with elevated metabolic rates when compared to other pure cold-blooded boney fish.

"Additional comparative data from other white shark tissues and/or from other endothermic shark species such as makos would be required to see if this general similarity in gene products holds," said Michael Stanhope of Cornell, who co-led the study with Shivji. "Nevertheless, this preliminary finding opens the possibility that some aspects of white shark metabolism, as well as other aspects of its overall biochemistry, might be more similar to that of a mammal than to that of a bony fish."

Shivji suggested that upon further genetic exploration of the white shark, there will be more surprises ahead.

"We've just scratched the surface in terms of investigating what makes these evolutionary marvels, and in many cases threatened species, tick," he said.