Green Blood Paper in Science Advances is out!
Green blood likely evolved multiple times in lizards
Our paper in Science Advances is out: "Multiple origins of green blood in New Guinea lizards". Thanks to Vivien Chua for the beautiful digitized Prasinohaema prehensicauda
Super excited to announce that our green blood paper is out in Science Advances. Check it out here: http://advances.sciencemag.org/content/4/5/eaao5017
Summary
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. This means that green blood likely emerged independently in different lizards, suggesting that green blood has beneficial properties. This and the isolated occurrence of green blood in several unrelated species of fish, frogs, and insects, supports the idea that green blood may have adaptive value (beneficial properties). Understanding how and why these lizards have evolved biliverdin retention and resistance to bile pigment toxicity will ultimately lead to non-traditional approaches to common health problems.
Press Releases
Our paper was picked up by several news outlets. Check them out for a non-scientific take on our lizards!
LSU Media Center by Alison Satake
LSU College of Science | The Pursuit Blogpost
I Fucking Love Science (IFLS) by Josh Davis
Reuters by Will Dunham
NPR Science by Nell Greenfieldboyce. Also check out our radio piece that will air on NPR's All Things Considered
Associated Press (AP) by Seth Borenstein; see also FoxNews
The Atlantic Science Column by Ed Yong
Science News by Susan Milius; see her previous article featuring our skinks here
ZMR Science by Tibi Puiu
The Independent by Josh Gabbatiss
Why Study Green Blood?
Biliverdin Toxicity
The top tube shows a blood sample from a red-blooded lizard from New Guinea (Lamprolepis smaragdina). The bottom tube reveals the bright green blood of Prasinohaema. The bile pigments in this blood is toxic to other species, but Prasinohaema handles it just fine. Credit: Chris Austin, LSU.
Green blood is one of the most unusual traits in the animal kingdom, yet it is the diagnostic trait of Prasinohaema, a genus of lizards only found in New Guinea. The muscles, bones, blood, tongues, and other tissues are stained bright lime green due to high levels of a bile pigment called biliverdin. However, this is a dangerous trait to have, because bile pigments are toxic to most vertebrates and cause jaundice. Surprisingly, these lizards remain perfectly healthy with levels of green bile pigments that are 10-20 times higher than the lethal concentration in humans.
Significance
In addition to having the highest concentration of biliverdin recorded for any animal, these lizards have somehow evolved a resistance to bile pigment toxicity. Understanding how and why these lizards have evolved biliverdin retention and resistance to bile pigment toxicity will ultimately lead to non-traditional approaches to common health problems. I think our research will lay the foundation for an integrative way to think about bile pigments tolerance and in doing so contribute to biomedicine and improve human health and economic development.
Basic Science
Prasinohaema virens, a low elevation species of green blooded lizard. Photo credit: Christopher Austin.
I think an important point deals with how basic research can reap great unintended rewards. Research on lizards from halfway around the world has implications for human health, thus our research shows how basic discovery science is important. Jaundice is a common problem for newborns, affecting half of all newborns, and anyone with liver/kidney issues. Importantly, our research will lay the foundation for an integrative way to think about bile pigments and jaundice and in doing so contribute to biomedicine and potentially improve human health down the road. This research was funded by the National Science Foundation that funds basic discovery science.
Why have green blood?
Prasinohaema semoni is a gray green blooded lizard that hangs out on tree trunks. The diverse ecology of Prasinohaema lizards makes it difficult to pinpoint the ecological pressures that shaped this unusual physiology. Photo credit: Christopher Austin.
That is the question of the day! The physiological and/or ecological importance of biliverdin accumulation is unknown. This enigmatic trait may or may not be an adaptation. It is, however, plausible that small increases in biliverdin conferred some selective advantage, and that over evolutionary time even greater concentrations of biliverdin conferred an even greater advantage. A closely related bile pigment (bilirubin) has been shown to be toxic to human malarial parasites. Our leading hypothesis is that excess biliverdin might create a toxic environment for blood parasites and deter harmful infections like malaria. We are working with Susan Perkins at the American Museum of Natural History to investigate this possibility.
What's Next?
We are currently looking into the genes responsible for the evolution of this unusual physiological trait. We think that understanding the genomic proteomic changes responsible for green blood will lead to a better understanding of jaundice and how to cure it.
Zach Rodriguez | LSU PhD Student
I am a PhD candidate at Louisiana State University's Museum of Natural Science. I consider myself an evolutionary biologist and herpetologist. I created this site to promote my research and interests.