Malaria and Green-Blooded Lizards

When scientists discovered six species of lizard on Papua New Guinea that evolved to have toxic, lime green blood, they were puzzled. The lizards' blood appears green as a result of extremely large doses of a green bile biliverdin[1]. These high concentrations of biliverdin in the blood overwhelms the crimson colour of red blood cells resulting in a lime-green coloration of the muscles, bones, and even their tongue.
After mapping the evolutionary family tree of New Guinea lizards the scientists found that green blood developed at four different points in history.

'These green-blooded lizards are not each other's closest relatives, and they all likely evolved from a different ancestor that had red blood', explains said evolutionary biologist Zachary Rodriguez. 'This means that green blood likely emerged independently in different lizards, suggesting that green blood has beneficial properties.'

The green blood probably gives the lizards an evolutionary advantage of some kind, said Christopher Austin of Louisiana State University[2].

Dr Austin thinks this could be why lizards evolved to be green-blooded, as malaria is an issue for lizards in New Guinea. It is possible the threat posed by malaria was so severe to past lizards that evolution heavily favoured animals with high levels of this toxic compound, which meant green blood became common in the animals.

Michael Oellermann, a researcher at the University of Tasmania in Australia, wondered what the evolutionary cost of having green blood may be. He believes there must be a price to pay, otherwise more critters would bleed green.

In humans, having elevated levels of biliverdin has been linked to reducing the growth of malaria parasites[3].

[1] Rodriguez et al: Multiple origins of green blood in New Guinea lizards in Science Advances – 2018 
[2] Austin, Perkins: Parasites in a biodiversity hotspot: a survey of hematozoa and a molecular phylogenetic analysis of Plasmodium in New Guinea skinks in Journal of Parasitology – 2006 
[3] Alves et al: Biliverdin targets enolase and eukaryotic initiation factor 2 (eIF2α) to reduce the growth of intraerythrocytic development of the malaria parasite Plasmodium falciparum in Science Reports – 2016

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