How poison frogs keep from poisoning themselves
Butch Brodie, an evolutionary biologist at the University of Virginia in Charlottesville who wasn’t involved in the research, said, “While other studies have identified genetic changes that give frogs resistance to particular toxins, this study ‘lets you look under the hood’ to see the full effects of those changes and how the frogs are compensating.”
Many poison dart frogs carry cocktails of toxic alkaloid molecules in their skin as a defense against predators.
These toxins, picked up through the frogs’ diets, vary by species. Here, researchers protein building blocks, or amino acids, changes the shape of the protein, which can prevent toxins from latching on. But making that change could have unintended side effects, too.”
For example, the toxin epibatidine binds to proteins that are usually targeted by acetylcholine, a chemical messenger that’s necessary for normal brain function.
So Tarvin and her colleagues looked at how this acetylcholine receptor protein differed between poison frog species that are resistant to epibatidine and some of their close relatives that aren’t. amino acid ‘switch’ that would make the resulting receptor protein resistant to epibatidine.
But epibatidine resistance wasn’t a straightforward deal, it turned out.
Study coauthor Cecilia Borghese, a neuropharmacologist also at the University of Texas at Austin, said, “We noticed that replacing one of those amino acids in the human [protein] made it resistant to epibatidine, but also affected its interaction with acetylcholine.
“Both are binding in the exact same region of the protein. It’s a very delicate situation.”
That is, the amino acid latch on, but that still responds normally to acetylcholine.
Tarvin added, “The resistance-giving amino acid change appears to have evolved three separate times in poison frogs.”
Three different lineages of the frogs have resistance to the poison, and all of them got that immunity by flipping the same switch.
But the amino acid changes that bring back a normal acetylcholine response aren’t the same across those three groups.
Brodie added, “It’s a cool convergence that these other switches weren’t identical, but they all seem to recover that function.”