"There's so much green pigment in the blood that it overshadows the brilliant crimson coloration of red blood cells", coauthor Chris Austin, a biologist at Louisiana State University, tells NPR. The excess of green bile pigment essentially eclipses the normal ruddy hue of their red blood cells.
But how did these lizards evolve to have all this green bile - which is usually toxic at high concentrations - in their systems?
If you ever examine the innards of a green-blooded skink, you might take a second (or even a third) look: The muscles, bones and even the tongues of these lizards have a bright, lime-green color - not from their diet, but because of the copious amount of green bile that's in their blood.
In the past, scientists had assumed that lizards with this green blood must belong to one closely related group.
"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. This happens as their entire bodies have high concentrations of biliverdin.
Ongoing work at LSU is examining the potential effect of the pigment responsible for green blood on the malaria parasite and others that infect the lizards, Perkins added.
Researchers in the study believe that understanding the physiological changes that have let the skinks be jaundice-free could lead to a better understanding of health problems caused by biliverdin. Two of the green-blooded species were newly discovered. The other species that sport green blood give birth to live young. 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.
The fact that green blood emerged independently on numerous occasions suggests it may be evolutionarily beneficial, according to the researchers.
What's more, he's personally eaten raw red-blooded skinks and green-blooded skinks, and found that both tasted about the same-kind of like "bad sushi", says Austin. They think that this means that the green blood may be a valuable adaptation. It's possible the green blood protects the animals from malaria, as in vitro studies have shown that human blood with high levels of bilirubin, a close relative, can stave off infection. Scientists have previously documented insect, fish and frog species that benefit from slightly elevated levels of biliverdin.