Poisons in nature are part of the natural defense of an organism, whether it is a plant or an animal---these toxins act as protection against predators. However, the discovery of these natural toxins by humans has led to their unique use by some cultures. For example, deep in the rain forests of western Colombia, the Emberá Chocó Indians practiced the custom of tipping darts with frog toxins for use with their blowguns in their hunt for big game. The dart tip is rubbed multiple times along the frog’s back, where the poison is secreted from glands within the skin. Blowguns, made from hollowed-out palm wood, are loaded with darts inscribed with spiral grooves to hold the poison.
The poison used by the Chocó is obtained from Phyllobates terribilis, a brightly colored golden yellow frog well-hidden in the jungles of the Pacific versant of Colombia. Although small—about 47 mm in length—this frog is about twentyfold more toxic than its relatives. If poison were to enter through a small wound during handling, the results could be fatal to man.
These dendrobatid frogs are the origin of the toxic steroidal alkaloids batrachotoxins (BTXs)—batrachotoxin, homobatrachotoxin, and batrachotoxin-A. Batrachotoxin blocks neuromuscular transmission irreversibly through ion channels found in heart and skeletal muscle and in nerve cells. Thus, the toxin prevents the conductance of the body’s electrical signals—think heart arrhythmias, fibrillation, and death.
The name batrachotoxin is derived from the Greek “batrachos,” meaning frog. The history of the discovery of batrachotoxin is an interesting one. Initially reported in isolated species of the frog genus Phyllobates (Latin for leaf climber in the family Dendrobatidae) in the 1960s, subsequent research in the 1990s showed that certain passerine birds from Papua New Guinea (e.g., the hooded pitohui and the blue-capped ifrit) contained feathers and skin from which batrachotoxin could also be isolated. To add to the mystery, poison-dart frogs raised in captivity on alkaloid-free diets have no detectable BTXs in their skin. Thus, the putative source of BTXs is from the diet of these frogs or birds—insects. It is thought that the dendrobatid poison frogs do not produce the toxin de novo, but most likely sequester the alkaloid from their diet.
What is most fascinating about poison-dart frogs is that they are resistant to the toxin. This allows the frogs to eat BTX containing beetles without harm and to sequester the toxin within its own body without any ill effects! This is attributed to a genetic modification of the very ion channels where the toxin produces its ill effects.
So, the saying, you are what you eat is undoubtedly true if you’re a poison dart frog.
Abstracted with permission from Lily Robinson and the Art of Secret Poisoning, nVision Publishing, 2011