Cuban brown anoles have the highest blood lead levels of any vertebrate known
Cuban Brown Anole Lizards Show Record-Breaking Tolerance to Lead Pollution
Some city-dwelling lizards are carrying a shocking biological secret: they may be the most lead-tolerant vertebrates ever documented.
Researchers at Tulane University discovered that Cuban brown anole lizards (Anolis sagrei) living in New Orleans not only survive but thrive with massive concentrations of lead coursing through their bloodstream. The findings, published August 6 in Environmental Research, highlight an unexpected case of wildlife resilience in one of the most polluted environments in the United States.
Lead Levels That Break Records
The study revealed that the brown anoles in New Orleans carry average blood lead levels of 955 micrograms per deciliter (µg/dl) — more than triple the levels previously recorded in Nile crocodiles, which until now held the record for the most lead-tolerant vertebrates.
What’s more astonishing is that while crocodiles showed clear symptoms of lead poisoning — including blackened teeth and signs of poor health — the anoles appeared outwardly healthy and unaffected.
“They’re doing just fine with levels that, frankly, in other organisms, would be killing them,” said evolutionary ecologist Alex Gunderson, the study’s senior author. One particularly shocking case recorded a lizard with a blood lead concentration of 3,192 µg/dl, levels so high that biologist Annelise Blanchette initially assumed her equipment was malfunctioning. But repeated testing confirmed the results.
For comparison, in humans, blood lead levels above 45 µg/dl typically require medical intervention. In children, no amount of lead is considered safe, as exposure can cause brain damage, developmental delays, and stunted growth.
Extraordinary Tolerance
Despite their staggering blood lead levels, the brown anoles did not show declines in basic physical performance. In treadmill tests, balance challenges, and endurance trials, the lizards matched the speed, agility, and stamina of non-contaminated reptiles.
When researchers exposed the anoles to even higher concentrations, they tolerated up to 10,000 µg/dl of lead before showing physical symptoms such as lethargy, loss of appetite, and reduced endurance.
This remarkable tolerance prompted genetic analyses, which revealed potential adaptations. The anoles appear to increase production of oxygen-carrying molecules, a possible countermeasure against lead’s interference with red blood cells’ ability to transport oxygen. By flooding their systems with more oxygen carriers, the lizards may be able to offset the toxic effects.
From Curiosity to Discovery
The breakthrough came almost by accident. Blanchette, then a graduate student at Tulane, had become curious about the Cuban brown anoles that dart across New Orleans neighborhoods. Previous research from Tulane scientists had shown that local mockingbirds carried measurable amounts of lead in their blood and feathers, reflecting the city’s legacy of industrial pollution and old lead-based paints.
But few expected the humble brown anoles — a species commonly found perched on fences, trees, and walls — to be record-breaking lead-resistance champions.
“It required some nerds who are interested in lizards to go out there and start measuring it,” Gunderson joked.
Implications for Science and the Environment
The discovery opens the door to new avenues of research in environmental biology, toxicology, and evolutionary adaptation. Understanding how Cuban brown anoles cope with extreme lead exposure could shed light on natural resistance mechanisms in vertebrates, with possible implications for human health studies.
It also underscores how urban wildlife is often forced to adapt to polluted environments in ways that scientists are only beginning to understand. While many species suffer population declines from exposure to heavy metals and other toxins, others may evolve surprising strategies to survive.
As Blanchette, now working at the U.S. Environmental Protection Agency, explains, the study could help guide future research on the long-term ecological impacts of pollution and how animals respond at the genetic and physiological level.
A Resilient Survivor in the City
For now, the Cuban brown anole remains an emblem of resilience, scuttling across New Orleans backyards with blood lead levels that would be fatal to almost any other animal. Their ability to adapt to one of the most toxic metals known to science highlights the complex relationship between urban wildlife and human-made pollution — and raises deeper questions about the hidden survival strategies of animals living in our cities.