Poison frogs produce toxins that plow down a nervous system. Get a tiny amount of the poison in your system, and you’re in for trouble. They manage this by storing up toxins ingested from their prey. And yet the frogs themselves are totally immune. How does a frog that stores and dispenses poison manage to avoid negative effects from its own lethal toxins? It’s actually a complex evolution of amino acid replacements, according to a recent study in the journal Science.
The frog neurotoxin epibatidine binds to acetylcholine receptors, which makes it difficult for frogs to gain a resistance to epibatidine. But one amino acid replacement that has evolved in three clades of poison frogs allows the amphibians a lower sensitivity to epibatidine, while still maintaining receptor functionality.
The study’s authors “found that the single amino acid change common to all the poison frogs made the receptor less sensitive to the toxin, yet also rendered it less responsive to acetylcholine, its endogenous ligand,” the Scientist magazine notes. “But the different combinations of additional amino acid substitutions observed in two of the groups of poison frogs recovered the receptor’s function, suggesting that these mutations compensate for the cost associated with avoiding self-poisoning.”
In other words, poison frogs are immune to the toxins because they have been able to reorganize how their nervous system works using amino acid replacements.