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Why some lizards have toxic lime-green blood

Lizards known as green-blooded skinks manage to remain healthy despite having levels of bile that are 40 times higher than the lethal concentration in humans.

Prasinohaema virens is a species of lizards in New Guinea that has high levels of a toxic green bile pigment called biliverdin, which makes the muscles, bones, and even the blood of these creatures appear bright, lime green.

Study lead author Zachary Rodriguez is a doctoral candidate in the Department of Biological Sciences at Louisiana State University.

“In addition to having the highest concentration of biliverdin recorded for any animal, these lizards have somehow evolved a resistance to bile pigment toxicity,” said Rodriguez.

“Understanding the underlying physiological changes that have allowed these lizards to remain jaundice-free may translate to non-traditional approaches to specific health problems.”

The researchers investigated the evolutionary history of green blood, which can be found in several groups of New Guinea lizards.

Working in the lab of Professor Chris Austin, the team examined 51 species of skinks. The experts found six species that had green blood, and discovered two species which were previously unknown.

“The green-blooded skinks of New Guinea are fascinating to me as a parasitologist because a similar liver product, bilirubin, is known to be toxic to human malaria parasites,” said study co-author Susan Perkins.

“Ongoing work with the Austin lab examines the potential effect of the green blood pigment on malaria and other parasites that infect these lizards.”

DNA analysis revealed four separate lineages of green-blooded lizards, and each of these lines evolved independently from a red-blooded ancestor.

“We were excited by the complex history of these animals and surprised by the breadth of green-blooded lineages across lizards,” said Rodriguez. The fact that green blood emerged repeatedly suggests that it has been naturally selected for some type of benefit.

Previous research has demonstrated that bile pigment can act as an antioxidant, terminating free radicals. Bile pigment is also linked to disease prevention during in vitro fertilization. As of now, however, the function of bile pigment in green-blooded lizards remains a mystery.

“Our next goal is to identify the genes responsible for green blood,” said Rodriguez.

The study is published in the journal Science Advances.

By Chrissy Sexton, Staff Writer

Image Credit: Chris Austin, LSU

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