What makes this dragon fierce

The world’s largest lizard – the Komodo dragon (Varanus komodoensis) – is no lazybones. Adults grow up to three metres in length and can track down and ambush prey they have sniffed from kilometres away.

Now, after a years-long effort to sequence the giant monitor’s genome, researchers have been given a glimpse of what’s behind these feats of endurance.

Komodo dragons are native to their namesake island of Komodo, in Indonesia, and a handful of others.

However, for this study an international team led by researchers from Gladstone Institutes, US, used blood collected from Slasher and Rinca, two Komodo dragons from Zoo Atlanta, to obtain DNA that was then sequenced. 

It’s the first time a member of the varanid lizard branch of reptiles has had its genome decoded. 

Unlike other members of their cold-blooded reptilian clan, varanid lizards are masters of endurance thanks to their mammal-like hearts and higher aerobic metabolic rates. Where other lizards tire easily, Komodo dragons can track prey over long distances and engage in vicious male-on-male contests.

The team found numerous chemical receptors, known as vomeronasal receptors, in the genome. One class of these receptors – which can sense hormones and pheromones – had 150 members throughout the genome, often in clusters.

“It will be interesting to determine whether this explains Komodo dragons’ ability to detect prey over such large distances,” says lead researcher Benoit Bruneau, from Gladstone Institutes.

Two hundred Komodo genes appeared to have undergone positive selection, which is to say that they have stood the test of evolutionary time because they are useful.

Of these, a handful pump out proteins that improve the output of mitochondria, the cellular powerhouses essential to aerobic fitness.

Other cardiac function genes, such as angiotensinogen genes that encode precursors of angiotensin cardiac regulators, were also under positive selection.

“Our analysis showed that in Komodo dragons, many of the genes involved in how cells make and use energy had changed rapidly in ways that increase the lizard’s aerobic capacity,” says biologist Abigail Lind from the Gladstone Institutes.

“These changes are likely key to the Komodo’s ability to achieve near-mammalian metabolism.”

Another class of genes that stood the test of time were genes that control blood clotting. The authors speculate that this might be to counteract their own anti-coagulant-laced saliva, which they are exposed to during combat.

The study was published in the journal Nature Ecology & Evolution.

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