Scientists Find Four Lineages of Green-Blooded Lizards in New Guinea

Several species of skinks (a type of lizard) from the island of New Guinea have lime-green colored blood — which in turn results in bright green muscles, bones, tongue, and mucous membranes, according to a team of researchers from Louisiana State University and the American Museum of Natural History.

Prasinohaema prehensicauda, a green-blooded lizard with high concentrations of biliverdin, a toxic green bile pigment. Image credit: Chris Austin, Louisiana State University.

Prasinohaema prehensicauda, a green-blooded lizard with high concentrations of biliverdin, a toxic green bile pigment. Image credit: Chris Austin, Louisiana State University.

New Guinean skinks with green blood are currently grouped into the same genus, Prasinohaema, based solely on blood coloration.

The rare coloration comes from exceptionally high concentrations of biliverdin, or green bile pigment. In mammals, it’s converted to the toxic bilirubin, which causes jaundice in human newborns.

Surprisingly, green-blooded lizards remain healthy with levels of green bile that are 40 times higher than the lethal concentration in humans.

“In addition to having the highest concentration of biliverdin recorded for any animal, these lizards have somehow evolved a resistance to bile pigment toxicity,” said Zachary Rodriguez, a doctoral candidate at Louisiana State University.

“Understanding the underlying physiological changes that have allowed these lizards to remain jaundice-free may translate to non-traditional approaches to specific health problems.”

To investigate the evolutionary history of green blood, Rodriguez and co-authors examined 51 species of Australasian skinks, including six species with green blood, two of which are undescribed new species.

The researchers analyzed DNA from a total of 119 individuals (27 green-blooded Prasinohaema skinks and 92 closely related red-blooded lizards).

They discovered that there are four separate lineages of green-blooded lizards, and each likely shared a red-blooded ancestor.

“We were excited by the complex history of these animals and surprised by the breadth of green-blooded lineages across lizards,” Rodriguez said.

Green blood likely emerged independently in various lizards, which suggests that green blood may have an adaptive value.

Slightly elevated levels of bile pigments in other animals, including insects, fish and frogs, have played potentially positive roles in these animals.

Previous studies have shown that bile pigment can act as an antioxidant scavenging free radicals as well as preventing disease during in vitro fertilization. However, the function of green bile pigment in these lizards is still uncertain.

“The green-blooded skinks of New Guinea are fascinating to me as a parasitologist because a similar liver product, bilirubin, is known to be toxic to human malaria parasites,” said Professor Susan Perkins, from the Sackler Institute for Comparative Genomics and the Division of Invertebrate Zoology at the American Museum of Natural History.

“Ongoing work examines the potential effect of the green blood pigment on malaria and other parasites that infect these lizards.”

The team’s results were published in the May 16, 2018 issue of the journal Science Advances.

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Zachary B. Rodriguez et al. 2018. Multiple origins of green blood in New Guinea lizards. Science Advances 4 (5); doi: 10.1126/sciadv.aao5017

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