The ubiquitous brown anoles that you’ve probably seen skirting around the nearest bush or tree are not only quick little roach killers, a recent study reveals that they are unaffected when exposed to levels of toxic lead that would hurt humans and other animals.
In fact, the tiny lizards have the highest lead tolerance of any vertebrate known to science.
Their ability to withstand the dangerous heavy metal — a common pollutant in urban environments — just might prove useful to human health down the line.
Lead exposure in humans, pets and wildlife can reduce cognition, harm reproduction, induce anemia, kidney, liver and heart disease. It also damages brain development in children.
A study of the lizards in New Orleans, conducted by biologists at Tulane University, showed that the invasive species is essentially not affected by lead levels in their blood and bones that would harm other animals.
In fact, lizards tested from a high-lead site in New Orleans had lead levels 10 times higher than those in the California condor, the largest bird in North America, which nearly went extinct due to lead exposure. Yet the New Orleans lizards where unfazed by the toxic heavy metal.
“We found that brown anoles in New Orleans have extreme blood lead levels and lead tolerance,” said the study.
New Orleans was an ideal location for the study because of decades of research into soil lead contamination across the city, said biologist Annelise Blanchette, the study’s lead biologist.
Neighborhood lizards
She and other researchers first captured anoles from different neighborhoods in New Orleans, some with high soil lead levels and some with low levels. The lizards, which measure 5 to 9 inches long and weigh about a quarter ounce, had corresponding high or low lead levels in their blood and bones.
A brown anole perches on a branch near the ground, where it can easily dart into the leaf litter below to hunt insects. (Courtesy Wayne Wang, Tulane University)
The neighborhoods had striking differences. The high-lead site produced lizards with blood lead levels more than 23 times higher than the lizards from the low-lead site.
Researchers then put the lizards through a series of physical challenges to test their balance, sprint speed, and endurance — skills known to be degraded by lead.
For balance they had the lizards run across a narrow 3.5-foot-long dowel and counted how many times the lizard slipped; for speed, they ran them up a steep 6-foot plank and for endurance they put them on a gentle treadmill until they faltered.
Researchers were surprised to find that the lizards that had “extreme field lead exposure” performed just as well as those with low lead exposure.
They then did genetic analysis of the anoles, knowing that lead impairs cells’ ability to transport and process oxygen, and found something unexpected. The lizards exposed to higher levels of lead seemed to express more genes that would increase a cell’s oxygen-carrying capacity.
“If lead is impairing the ability of cells to transport oxygen to all of the places it needs to be, maybe one way these lizards mitigate that is by expressing these genes that increase the oxygen-carrying capacity of cells,” said Blanchette.
Blanchette also ran a parallel experiment where she exposed anoles from a low-lead neighborhood to various intensities of lead over time in a lab, and then ran them through the physical challenges. The results were the same — the lead had little effect.
Human connection
Any human health benefit gleaned from the anole’s lead resistance would be a long way off, said Blanchette, but it’s possible researchers in the future would figure out how anoles are genetically coping with extremely high lead levels. Is that ability unique to anole or reptiles? How do mammals differ?
“If researchers can figure out what that difference is, what makes them unique and able to cope, we might be able to then turn and look at mammal genomes, genetics, and say, ‘Okay, this is where the difference is.’ That could be eventually useful in medicine for humans.”
Future medicines might interact directly with the genome and prevent lead from binding to cells, said Blanchette.
Where does the lead come from?
Though high lead levels are common in many urban areas, New Orleans is unique. It’s an old city, which allows lead to accumulate in the soil.
“Unfortunately, a lot of the old houses are still painted with lead-based paint, and hurricanes like Hurricane Katrina, anytime a hurricane comes through, paint is taken off. It gets incorporated into the soil, and it just stays there,” said Blanchette.
Heavy industry along the Mississippi also has contributed to lead levels, as has leaded gasoline. The EPA banned leaded gas for on-road vehicles in 1996, but, said Blanchette, “Those isotopes that were released from its use settled into the soil, and they don’t break down and and so it just stays there, where now humans and wildlife can be exposed to it.”
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She and other researchers suspect the lizards both inhale contaminated dust and likely ingest lead in their diet.
Brown anoles tend to perch close to the ground and dart into leaf litter to nab insects. Those bugs are likely covered in lead-contaminated dust.
Brown anoles are actually native to Cuba and invasive in the U.S.
They first showed up stateside in the 1880s, in the Florida Keys. Since then they’ve thrived in Florida, claiming underbrush as their territory, pushing native green anoles into the treetops, and expanding their range from South Carolina to Texas.
The next phase of research at Tulane is to see if the tree-top dwelling green anoles have lower lead levels than the more terrestrial brown anoles.
Bill Kearney covers the environment, the outdoors and tropical weather. He can be reached at bkearney@sunsentinel.com. Follow him on Instagram @billkearney or on X @billkearney6.
