A joint report alleging that a poison dart frog toxin has beenlinked to the death of Russian opposition leader Alexei Navalnyrippled quickly around the globe among scientists.
The allegations raised fresh questions about the circumstances of Navalny's 2024 death and about the origin of a highly unusual toxin.
Poison dart frog species have long fascinated researchers and the public, partly because of their diminutive size and striking color patterns and also because of the myths surrounding the deadly toxins found on their bodies.
But the toxin reportedly identified in this case – epibatidine – isn't known to have been used to kill anyone, Kyle Summers, an emeritus biology professor at East Carolina University, told USA TODAY.
Thereport released Saturday by the United Kingdom,Germany, France, Sweden and The Netherlands stated the governments were "confident" Navalny was poisoned, based on the traces of epibatidine found in his body. Navalny, an attorney,had been imprisoned in Siberia when he died. The report noted the toxin is only found naturally in poison dart frogs in South America, not Russia. The governments didn't release toxicology reports and the Russian government denied the allegation.
Epibatidine intrigued researchers for decades and was once highly sought after as a potential analgesic many times more powerful than morphine. It may be possible a chemical laboratory thousands of miles from a tropical rain forest could have artificially reproduced the toxin, but many questions remain, Summers said.
Daily diets of poison dart frogs in the wild cause deadly toxins
How did we learn about toxins in poison dart frogs?
John Daly, a biological chemist at the National Institutes of Health, pioneered the study of the dart frog toxins species during decades of research, tracing the origin of the poisons to the frogs' diets, according to Joe Schwarcz, director ofthe McGill University Office for Science and Society. He traced the origin of the poisons to the frogs' diets.
Enzymes in the frogs' bodies turn the alkaloids in ants, small beetles, millipedes and mites into toxins, Schwarcz wrote in an article first published in the Montreal Gazette. Daly identified epibatidine in a poison frog in Ecuador calledEpidedobates tricolor.
At first, researchers had high hopes for the poison. Although it's extremely toxic, they found it had a painkilling effect 200 times more potent than morphine and might not be linked to addiction.
The idea that epibatidine could be "a potentially useful pharmacological tool as a painkiller really stimulated a lot of interest and motivation," Summers said. "Ultimately it could be incredibly profitable if they could make it work as a painkiller."
Scientists were able to decode the toxin and chemically reproduce it, but they found the difference between a beneficial dose and a deadly dose was too narrow to be viable.
Could the epibatidine reportedly found in Navalny's body be manmade?
Although some Indigenous tribes in the rainforests were known to use batrachotoxin from dart frogs for hunting, scientist haven't found any evidence that epibatidine was ever used for that purpose.
Summers noted the statement from the governments does not make clear Navalny's cause of death, but it's remarkable if they were able to identify the epibatidine in samples from his body.
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It would be "very surprising" if anyone tried to use the product as an experimental chemical to poison someone, Summers said.
The statement from the UK and other governments said they informed the Organisation for the Prohibition of Chemical Weapons of their findings that could indicate violation of the Biological and Toxin Weapons Convention. It also stated the findings raise concerns that Russia had not destroyed all of its chemical weapons.
What to know about poison dart frogs
Found in tropical rain forests in South America, the frogs face risks from habitat destruction and the exotic pet trade. More than 175 species have been identified. Dart frogs in captivity aren't generally toxic because they aren't fed the same diet as frogs in the wild, the researchers found.
Colorful patterns on the frog warn predators of danger, said Summers. They advertise the toxins so that predators know to avoid them, he added. The frogs have evolved to be resistant to the toxins.
The bright colors are sometimes mimicked by non-poisonous frogs to convince predators they're deadly and by other poisonous frogs to join forces in warning predators away, said Summers, one of a number of scientists who have studied coloration among dart frogs for years.
Color also is used in mate choice and competition, Yusan Yang, an assistant professor at the University of South Florida, told USA TODAY.
Females usually prefer males that have the same color as their own as well as brighter colors. And males are more aggressive when the opponent is the same color, and brighter.
Many of the poison frog species are different from other frogs, who abandon their eggs to hatch on their own, Summers said. He and Yang described how the adults cooperate to transport their tadpoles to small pools.
"The tadpoles will wriggle on to the male's back and the male will go to a small pool," Summers said. "Over a period of months they will go back and visit the pool."
Females lay eggs for the tadpoles to eat and survive, the scientists said. That kind of monogamous pairing is "very unusual for frogs," Summers said.
The behaviors for mating are likely acquired when tadpoles remember the mom's color when she is feeding them, Yang said, and when they grow up they show bias toward the color that they remember.
Dinah Voyles Pulver, a national correspondent for USA TODAY, covers climate change, wildlife and the environment. Reach her at dpulver@usatoday.com or @dinahvp on Bluesky or X or dinahvp.77 on Signal.
This article originally appeared on USA TODAY:Assassination by frog? Scientists ponder a Navalny report.
