Green-blooded lizards pose evolutionary puzzle

SETH BORENSTEIN
Washington, US | May 16

For some lizards it’s easy being green. It’s in their blood. Six species of lizards in New Guinea bleed lime green thanks to evolution gone weird. It’s unusual, but there are critters that bleed different colors of the rainbow besides red.

The New Guinea lizards’ blood — along with their tongues, muscles and bones — appear green because of incredibly large doses of a green bile pigment.

The bile levels are higher than other animals, including people, could survive. Scientists still don’t know why this happened, but evolution is providing some hints into this nearly 50-year mystery.

By mapping the evolutionary family tree of New Guinea lizards, researchers found that green blood developed inside the amphibians at four independent points in history, likely from a red-blooded ancestor, according to a study in Wednesday’s journal Science Advances. T

his isn’t a random accident of nature but suggests this trait of green blood gives the lizards an evolutionary advantage of some kind, said Christopher Austin of Louisiana State University.

“Evolution can do amazing things given enough time,” Austin said. “The natural world is a fascinating place.” Austin first thought that maybe being green and full of bile would make New Guinea lizards taste bad to potential predators.

“I actually ate several lizards myself and they didn’t taste bad,” Austin said. He also fed plenty of them to a paradise kingfisher bird with no ill effects except maybe a fatter bird.

Understanding bile is probably key. Blood cells don’t last forever. After they break down, the iron is recycled for new red blood cells, but toxins are also produced, which is essentially bile.

In the New Guinea lizards, levels of a green bile pigment are 40 times higher than what would be toxic in humans. It’s green enough to overwhelm the color of the red blood cells and turn everything green, Austin said.