Green-blooded lizards living on New Guinea were thought to all have descended from one ancestor, but according to Reuters, a new genetic analysis suggests the trait arose independently four times.
The lizards, called skinks, have green blood due to high levels of the green bile pigment biliverdin, which also turns their muscles, bones, and mucosal tissues a green hue, Reuters adds.
A team from Louisiana State University and the American Museum of Natural History performed phylogenetic analysis of 24 green-blooded skinks and 95 closely related species, as they report this week in Science Advances. To their surprise, the researchers found some green-blooded lizards were more closely related to red-blood lizards. "Our key finding was that green-blooded lizards are not each other's closest relatives, and they all likely evolved from an ancestor that had red blood," LSU's Zachary Rodriguez tells Reuters. "This means that green blood likely emerged independently in different lizards, suggesting that green blood has beneficial properties."
But what that advantage is isn't yet clear, according to New Scientist. These lizards harbor biliverdin levels that are 40 times the lethal dose for humans, it adds, and while it the researchers suspect that it might offer some protection from malaria, some lizards still contract the disease. "We don't know the answer yet," LSU's Christopher Austin tells New Scientist. "There must be some selective advantage."