Published: Thu, May 17, 2018
Research | By Jody Lindsey

Why Do These Lizards Have Toxic Lime-green Blood?

Why Do These Lizards Have Toxic Lime-green Blood?

A odd genus of skink belonging to the species Prasinohaema has unusual green blood that has incredibly toxic properties.

"In addition to having the highest concentration of biliverdin recorded for any animal, these lizards have somehow evolved a resistance to bile pigment toxicity", Zachary Rodriguez, a biologist from Louisiana State University (LSU), said in a statement.

Biliverdin appears whenever hemoglobin, the particle that transports oxygen, breaks down to produce bilirubin, another bile pigment. In humans, and, indeed, all other vertebrates, chronic accumulation of these pigments in the blood causes jaundice. Puncture a member of the Prasinohaema, a genus of skinks, and you'll get a flow of green blood instead. Yet they suffer no ill effects. The answer could provide new insights into human illnesses like jaundice and malaria.

"I find it just absolutely remarkable that you've got this group of vertebrates, these lizards, that have a level of biliverdin that would kill a human being, and yet they're out catching insects and living lizard lives", says Susan Perkins, a researcher at the American Museum of Natural History in NY. How the lizards avoid developing the condition unknown. But in a new Science Advances study, a team of biologists reveal that they've uncovered the evolutionary history of the skinks' green blood, which may offer some clues into how we can use it too.

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In the past, scientists had assumed that lizards with this green blood must belong to one closely related group. Until now, their evolutionary relationship has been unclear. They examined 51 species of skinks, which included six species with green blood, two of which are species new to science. They all evolved separately but had a common ancestor with red blood.

Scientists are now trying to understand how these lizards might benefit from blood that's green.

Now that a thorough analysis of the has been done, the stage is set, as it were, for further analysis into the role natural selection may have played in shaping this curious trait, as well as understanding the genetic and biochemical basis for the lizards' remarkable lack of jaundice. "The problem is that there's green-blooded lizards that aren't green, and there's red-blooded lizards that are green", he explains. The fact that green blood emerged independently four times in separate lineages suggests that it must have had an adaptive value, but the team isn't quite sure what that value is yet.

Lately the scientists have been wondering if the lizards' green blood might protect them from parasites like malaria - although Austin admits that this is "pretty speculative".

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