This story was originally published by the Louisiana Illuminator.

Something remarkable is happening with the little brown lizards that have taken over the urban landscape of New Orleans. They’re living – and even thriving – with levels of lead in their blood that scientists say should be lethal to creatures that are far bigger, both two- and four-legged. 

A new Tulane University study on brown anoles could offer a better understanding of lead poisoning, how doctors can treat it and how wildlife evolves to live within an increasingly urban world, according to the researchers behind the findings. 

Doctors say there is no safe level of lead in blood for humans. When children are tested, the safe threshold is less than 3.5 micrograms per deciliter of blood. Lead levels above 45 micrograms require urgent medical attention and treatment. 

The average per-deciliter lead level in the lizards Tulane tested was 955 micrograms, according to the new research. 

“I was shocked,” said Annelise Blanchette, a U.S. Environmental Protection Agency biologist who spearheaded the study for her doctoral thesis in evolutionary biology at Tulane University. 

Older cities such as New Orleans deal with a long legacy of lead pollution from abandoned storage sites for leaded gasoline and lead-based pipes and paint that permeates its way into the soil. Lead doesn’t decompose over time, meaning its contamination risk remains indefinitely.

Children who are exposed to even low levels of lead face a risk of developmental delays, behavioral issues and damage to the brain, heart and kidneys.

Blanchette originally set out to discover how pollutants such as lead affect wildlife and focused on brown anoles out of convenience. Scientists say the anoles breathe in lead from the air and ingest it through the contaminated insects and water they consume.

“With the lizards being everywhere, so commonplace and being really great models in the lab, easy to keep in the lab, they were just kind of the natural next step,” she said. 

Brown anoles have spread across the eastern United States over the past 150 years, migrating aboard ships from Cuba and the Bahamas. They were first recorded in the Florida Keys in the 1880s and expanded rapidly throughout America in the 1940s. They’re believed to have established a foothold in New Orleans during the 1990s and have become the dominant low-level lizard since then, according to the Tulane study. 

The species thrives in suburban settings, where they have forced their cousins, the green anole, higher up into the treetops while the brown variety lives and hunts on the ground. Brown anoles have been mapped in 13 Louisiana parishes, concentrated in the southeastern part of the state. 

Blanchette said she had no idea she would find the anoles to be so hearty with such high amounts of lead in their bodies. Lizards collected in the field had the highest average and individual blood-lead concentration levels ever recorded in a wild mammal, bird, fish, amphibian or reptile, she said, making them the most lead-tolerant vertebrate currently known to science. 

“Everything else would be dead,” said Tulane assistant professor Alex Gunderson, who’s Blanchette’s adviser and co-author of the study. 

Beyond just surviving with such extreme levels of lead in their blood, the anoles showed no sign of typical lead poisoning— measured in loss of balance, speed and endurance when moving — until exposed to a level of lead in their blood nearly 10 times higher than scientists recorded in the wild. 

“I was absolutely shocked, but it was also very exciting because I knew then that the questions that we were interested in asking would be really interesting to answer,” said Blanchette. “These lizards could really potentially give us a lot of insight into lead tolerance and exposure.”

Beyond even a better understanding of the toxin itself, lead-resistant lizards could also offer hints as to how and why some creatures are better at adapting to a more polluted, human-heavy environment. 

“Clearly, they’re capable of handling toxic conditions that tend to be prevalent in human environments,” said Yoel Stuart, an evolutionary biologist and associate professor at Loyola University in Chicago. He has studied another type of anole to understand how the lizards evolve and just how quickly they are changing. 

To verify that the lizards are indeed adapting to higher levels of lead, Stuart said replicating the Tulane study in other locales could help answer unknown questions and inform efforts to prevent extinction for more vulnerable species as the world faces a critical loss of biodiversity. 

“I would love to know: If you feed a bunch of lead to a brown anole from a place where there’s as little lead as you can find, how do they do?” Stuart said. “If [New Orleans anoles] die at way lower levels than these lizards, that suggests that the New Orleans lizards have adapted. If the brown anoles [in another location] happen to be more resistant, then it could be that they’ve always had the right tools to deal with lead.”

Blanchette said researchers have some theories as to how brown anoles can handle such extreme levels of lead, such as producing more red blood cells to counteract the effect lead has on carrying oxygen throughout the body. But it’s also possible brown anoles deal with lead in a way that has nothing to do with oxygen, she said.

Either way, the findings could be big. 

“Is it something that we can expect lots of species to be able to do, or a subset of species to be able to do? That can inform conservation strategies,” Stuart said. “It might help us target places where we need to mitigate lead in the environment.”

Gunderson said finding an animal so tolerant to such a potent toxin indicates their bodies are doing something humans don’t fully understand — and need to study. He spoke to the importance of broad exploration in research, adding that unexpected findings such as this uncover secrets that might have otherwise remained hidden.

“I don’t think anyone would have expected lizards to be this lead-tolerant,” he said. “It’s important to study everything … you don’t know what you don’t know, right?”