The Lizards With Lime-Green Blood

Mindy Sparks
May 17, 2018

In the latest study, a team led by Zachary Rodriguez from Louisiana State University, US, has brought us a step closer to unpacking the mystery, with research revealing that green blood evolved independently in the Prasinohaema genus four times.

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 coloration of their blood, muscles, bones and mucosal tissues, said LSU biologist Christopher Austin, a curator at the museum.

"We were excited by the complex history of these animals and surprised by the breadth of green-blooded lineages across lizards", Rodriguez said. The team is hoping that by continuing to study the elevated biliverdin levels in the lizards they can better understand the benefits of having green blood in the first place - and whether there's anything humans can learn from it. However, the function of green bile pigment in these lizards is still uncertain.

Rodriguez and colleagues analysed the genome data and conducted a phylogenetic and ancestral state character reconstruction in 24 individual lizards from six species in the genus, along with 95 related Australasian lizards with normal red blood.

Another green skink (Prasinohaema virens) that has green blood and lives in the lowlands of New Guinea.

A group of lizards inhabiting the island of New Guinea boasts one of the most exotic traits of any animal: green blood. In humans, high levels of a similar bile pigment called bilirubin make people sick with jaundice, but the lizards seem unaffected. But these lizard species don't look alike and have different lifestyles, with some laying eggs and others giving birth to live young. They discovered that there are four separate lineages of green-blooded lizards, and each likely shared a red-blooded ancestor. The study was published in the American journal, Science Advances on May 16.

The researchers figured that the greens in these lizards does not arise as a single cluster but are scattered among reds. "Evolution can do fantastic things given enough time", Austin said. Multiple origins of green blood in New Guinea lizards.

He notes that test tube experiments have shown that moderately elevated levels of bilirubin seem to protect against human malaria infection - and hundreds of malaria species are known to infect lizards. Several fish, frog and insect species also are green-blooded.

A blood that is so toxic, these reptiles are perfectly healthy.

"It's rare in the animal kingdom", says Rodriguez, "but because it does appear, this suggests there has to be some beneficial properties to green blood".

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