Lizards' Green Blood Evolved Four Times

Modesto Morganelli
Mag 17, 2018

Kermit the Frog used to sing that it wasn't easy being green, but that isn't the case for some real-life lizards. This is the only species of green-blooded skink that lays eggs. To their surprise, the results show that green blood evolved independently on at least four separate occasions.

A few lizards have a unusual secret: they have lime-green blood pumping through their arteries. The answer could provide new insights into human illnesses like jaundice and malaria. This green blood makes their muscles, bones, tongues and the insides of their mouths green. The green comes from biliverdin, a byproduct of dying red blood cells.

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.

In the past, scientists had assumed that lizards with this green blood must belong to one closely related group.

"They have other cool traits such as giving birth to live young and adhesive toe pads", Rodriguez added.

Prasinohaema virens, a green-blooded skinkCHRISTOPHER AUSTINTo find out how the trait arose in lizards, Austin and his colleagues examined the genomes of 51 species of skinks, including six with green blood.

It turns out that the green-blooded lizards are not each other's closest relatives, according to a report in the journal Science Advances. 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.

"There really is a fundamental objective of this trait", says Perkins. "We just don't necessarily know exactly what it is right now".

Austin tells NPR that the biliverdin likely didn't give the animals an advantage in deterring predators, as animals are able to eat the skinks without untoward GI troubles (he himself ate them, saying it was like "bad sushi").

Another possible benefit the researchers considered was that all the extra green made for better camouflage in green leaves. There are hundreds of species of malarial parasites that infect lizards, Austin says, so they need any help they can get.

If the green blood is protective against malaria, it's not perfectly so, because they've found a malarial parasite living inside a green-blooded lizard, says Perkins. Still, they're continuing to explore what kind of relationship there might be between malaria and green blood.

"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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