We Still Don't Know Why These Lizards Have Lime-Green Blood

Postado Mai 17, 2018

This is the only species of green-blooded skink that lays eggs.

A study published Tuesday suggests seems that this lime-green blood has evolved independently several times in lizards.

Prasinohaema prehensicauda, a green-blooded skinkCHRISTOPHER AUSTINSeveral species of New Guinea skinks, a type of lizard, are just as colorful inside as they are outside-bright green blood runs through their veins, an oddity among animals. "The lizards should be dead", says Christopher Austin at Louisiana State University in Baton Rouge, who has studied them for decades. "The bones are green, the muscles are green, the tissues are green, the tongue and mucosal lining is green". The green comes from biliverdin, a byproduct of dying red blood cells.

"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. It turned out that numerous species with green blood aren't closely related to one another, and have more in common phylogenetically with red-blooded skinks. The other species that sport green blood give birth to live young.

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. Researchers report in Science Advances today (May 16) that green blood likely arose in lizard lineages four different times. This particular group of lizards might somehow be predisposed to evolving green blood, says Austin.

"There really is a fundamental goal of this trait", says Perkins.

We already know the broad mechanism.

Austin initially thought that the buildup of biliverdin might deter predators by making the lizards distasteful.

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.

Another possible benefit the researchers considered was that all the extra green made for better camouflage in green leaves.

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".

The team's leading hypothesis is that the toxic green blood provides some protection against malaria, as higher than normal levels of biliverdin in human blood are known to kill malaria parasites.