Not all blood is red. Some species of squid, mollusks and crustaceans have clear blood that turns blue in the presence of oxygen. Seaworms and brachiopods bleed purple. Some segmented worms have blood with a greenish hue. But for most vertebrates – a group that includes all animals with a backbone, such as mammals, fish, birds, reptiles, and amphibians – their blood turns red due to the hemoglobin used to transport oxygen.
But that's not the case For all Backbonbon creatures: A group of skinks living in New Guinea and the Solomon Islands have lime-green blood. Now the researchers are starting to figure out how and why the small reptiles developed such a vital and vital vital fluid, Ed Yong reports The Atlantic.
The lizards, which are all classified in the genus . Prasinohaema (meaning "green blood" in Greek) was discovered in 1
As Austin NPR's Nell tells Greenfieldboyce, the green color of lizards is not limited to their blood. "The bones are green, the muscles are green, the tissues green, the tongue and the mucosa green," he says.
This is because they are stewed in a green pigment called biliverdin. "There is so much green pigment in the blood that it overshadows the bright red color of the red blood cells," says Austin.
For most animals, Yong explains, the hemoglobin cells die after about four months. The liver collects them and removes the iron, creating the green waste product biliverdin, which is later processed into yellow bilirubin. If too much of these toxins build up in the blood, it can cause a yellowing of the skin called jaundice. If excess amounts of the pigments accumulate, this can be fatal.
But not for Prasinohaema Lizards
They can go on despite the 20-fold higher concentration of biliverdin ever found on a human. And for the person the level was deadly.
By looking at the genetic relationships of these lizards, researchers determined how this strange adaptation developed. The team studied the genomes of 51 Skink species, including 27 individuals from six species of Greenbloods and 92 Redbloods.
Surprisingly, the greenbloods were not closely related. Instead, they were more closely related to Redblood, and the analysis suggests that the Greenblood feature has evolved at least four times. The study appears in the journal Science Advances.
Overall, the study suggests that there is an evolutionary benefit of having green blood from different habitats, all evolved over time . "There is a fundamental purpose to this feature," says co-author Susan Perkins of the American Museum of Natural History, Greenfieldboyce. "We just do not know exactly what it is."
The team hypothesized that biliverdin could make the lizards uncomfortable for predators, but the birds are not deterred by the stuff. And as Greenfieldboyce reports, Austin has eaten both red-blooded and green-blooded skinks. He says they both taste the same – disgusting.
The researchers also thought that the green could give the lizards an extra camouflage. But not all skinks with green innards are green on the outside.
Her current, admittedly speculative, hypothesis is that biliverdin-rich blood protects against parasites. People with elevated bilirubin, Greenfieldboyce reports, have added protection against malarial parasites. Lizards, it turns out, are susceptible to hundreds of malaria species and the green blood could protect against some of them.
But it's a tricky idea to test. "The naive view is that if green blood were developed to prevent malaria, there would be no malaria in green-lipped lizards," explains Austin Yong. But the lizards get malaria. One explanation for this could be that a strain of parasites has also developed to overcome defenses and infect lizards with malaria in a constant evolutionary arms race.
Whatever the reason is that the skinks have green blood, the fact that they can survive so much biliverdin is interesting and could provide biomedical findings, says Adriana Briscoe of the University of California in Irvine, who does not the study was involved, Yong. Briscoe points out that studying the creatures could lead to new treatments for diseases such as jaundice and malaria.
The researchers are now trying to find out which of the genes of the lizards produces all the green through their veins.
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