Magazine article Science News

It's Not Easy Being Green-Blooded

Magazine article Science News

It's Not Easy Being Green-Blooded

Article excerpt

"Dark lime green" is how biologist Zachary Rodriguez describes the blood of the Prasinohaema lizards of New Guinea and surrounding islands. "Vivid," he adds.

With green blood comes Granny Smith-colored muscles and bones and a bluegreen mouth, exposed during defensive posturing. But the strangest thing about the five species of Prasinohaema lizard is that they can live like that.

Lime, apple and avocado can be risky blood colors. They indicate that these lizard species build up a toxic substance called biliverdin. The lizards' red blood cells still depend on hemoglobin, the stuff that ferries oxygen and makes most animal blood red, but any lizard-blood redness is overwhelmed by massive concentrations of the green biliverdin. A breakdown product of hemoglobin, biliverdin gives the greenish edge to bruised human flesh. Most animal bodies quickly whisk it away.

High concentrations of biliverdin, say over 50 micromoles per liter, make humans sick with jaundice. The lizards, however, do just fine with 714 to 1,020 [micro]M/L.

It's tempting to wonder if evolution has favored green blood because toxic biliverdin might make predators spit out any lizard they start to bite. Not so, based on current evidence, Rodriguez says. An old test found that a predatory bird and a snake relished green-blooded lizards; he's heard that cats love them, too.

Plenty of other ideas are still in play, among them: The biliverdin may reduce susceptibility to malaria or to cell damage from the sun's ultraviolet rays, or even add some extra camouflage for life in trees. …

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