Experts seek secrets of green-blooded lizards

High concentration of green bile pigment in their blood results in a striking lime-green colouration

Agroup of lizards inhabiting the island of New Guinea boasts one of the most exotic traits of any animal: green blood.

And scientists have been trying hard to figure out what benefit this characteristic — caused by high levels of an ordinarily toxic green bile pigment — may give them.

But these lizards are beginning to give up some of their secrets, including their evolutionary history. Researchers said on Wednesday a DNA study resolved their family tree, finding that green-bloodedness evolved four different times among lizards called skinks on New Guinea.

“Our key finding was that green-blooded lizards are not each other’s closest relatives, and they all likely evolved from an ancestor that had red blood. This means that green blood likely emerged independently in different lizards, suggesting that green blood has beneficial properties,” said evolutionary biologist Zachary Rodriguez of Louisiana State University’s Museum of Natural Science.

The high blood concentration of the green bile pigment biliverdin overwhelms the intense crimson colour of red blood cells, resulting in a striking lime-green colouration of their blood, muscles, bones and mucosal tissues, said LSU biologist Christopher Austin, a curator at the museum.

High levels of biliverdin cause jaundice in most animals. But these lizards thrive despite biliverdin levels many times greater than the lethal concentration in people.

Scientists remain uncertain about the advantage green blood may provide the lizards. Several fish, frog and insect species also are green-blooded.