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Amphibians


Frogs acquire the toxins needed for chemical defense by either producing them through glands on their skin or through their diet. The source of toxins in their diet are primarily arthropods, ranging from beetles to millipedes. When the required dietary components are absent, such as in captivity, the frog is no longer able to produce the toxins, making them nonpoisonous. The profile of toxins may even change with the season, as is the case for the Climbing Mantella, whose diet and feeding behavior differ between wet and dry seasons.

The evolutionary advantage of producing such toxins is the deterrence of predators. There is evidence to suggest that the ability to produce toxins evolved along with aposematic coloration, acting as a visual cue to predators to remember which species are not palatable.

While the toxins produced by frogs are frequently referred to as poisonous, the doses of toxins are low enough that they are more noxious than poisonous. However, components of the toxins, namely the alkaloids, are very active in ion channels. Therefore, they disrupt the victim's nervous system, making them much more effective. Within the frogs themselves, the toxins are accumulated and delivered through small, specialized transport proteins.

Besides providing defense from predators, the toxins that poison frogs secrete interest medical researchers. Golden frogs, of the Bufonidae family, secrete batrachotoxin. This toxin has the potential to act as a muscle relaxant, heart stimulant, or anesthetic. Multiple species of frogs secrete epibatidine, whose study has yielded several important results. It was discovered that the frogs resist poisoning themselves through a single amino acid replacement that desensitizes the targeted receptors to the toxin, but still maintains the function of the receptor. This finding gives insight to the roles of proteins, the nervous system, and the mechanics of chemical defense, all of which promote future biomedical research and innovation.