Why These Poison Frogs Don’t Poison Themselves
With support from the National Geographic Society, National Geographic Explorer Rebecca Tarvin’s team revealed a complex, evolutionary trend in Neotropical poison frogs.
What permits a small genus of Neotropical poison frogs to cover themselves in toxins that are lethal to other animals, and, in some cases, are 200 times more potent than morphine, yet not succumb to the toxins themselves?
In a paper published online yesterday in Science, National Geographic Explorer Rebecca Tarvin and her team describe the evolutionary history and mechanism of resistance to the toxin epibatidine in a subgroup of poison frogs. To keep predators from eating them, the frogs use the toxin, which binds to receptors in an animal’s nervous system and can cause hypertension, seizures, and even death.
Epibatidine has been the subject of intense medical research since its discovery in Ecuador in 1974, yet no drugs based on epibatidine have been successfully developed because of the extreme potency of this chemical. Thus, Tarvin and team aimed to discover how these poison frogs use this chemical without poisoning themselves.
The researchers discovered that a small genetic mutation in the frogs — a change in just three of the 2,500 amino acids that make up the receptor — prevents the toxin from acting on the frogs’ own receptors, making them resistant to its lethal effects. Not only that, but precisely the same change appeared independently three times in the evolution of these frogs.
“Being toxic can be good for your survival — it gives you an edge over predators. So why aren’t more animals toxic? Our work is showing that a big constraint is whether organisms can evolve resistance to their own toxins. We found evolution has hit upon this same exact change in three different groups of frogs, and that, to me, is quite beautiful.”
Given that the receptor that epibatidine acts on is also involved in pain and addiction, this discovery could help scientists looking for better pain relievers or anti-smoking drugs.
Funding for this project was provided by the National Geographic Society, the National Science Foundation, the UT Waggoner Center for Alcohol and Addiction Research, the National Institutes of Health and seven academic societies.