Toxic animals such as birds and frogs have evolved a strategy for avoiding harm, but not in the way scientists expected.
A tiny, drab bird with a terrible secret dwells in the jungles of New Guinea. The hooded pitohui is a poisonous bird whose orange and black feathers are loaded with poison.
Touching a pitohui’s feathers is enough to set your hands on fire. When you swallow a small amount of batrachotoxin, or BTX for short, the poison blocks your sodium channels, resulting in paralysis and even death.
“These toxins can be thought of as a natural drug. It’s something that animals use to protect themselves because it… either gives the thing that’s trying to eat them a very unpleasant feeling or in the worst case, kills the thing that’s trying to eat them,” according to Daniel Minor, a biophysicist at the University of California, San Francisco’s Cardiovascular Research Institute.
The pitohui, according to scientists, does not produce its own poisons and instead obtains them from its small beetle meal. The same process is thought to be at work in Central and South American poison dart frogs, which also have BTX in their brilliantly colored skin.
All of this raises an important question: how do toxic creatures like the pitohui save themselves from poisoning?
For decades, the best explanation has been that birds and frogs evolved particularly adapted sodium channels that are immune to BTX. Nerves, brain cells, and muscle cells all need sodium channels to function correctly. After all, animals like Egyptian mongooses, which can withstand cobra venom, are examples of creatures who use this strategy to avoid poisons.
But, according to a research published in the Journal of General Physiology, this is not the case.
The researchers show that pitohui and poison frogs contain “toxin sponges,” or proteins that scavenge deadly poisons before they cause harm.
Providing proof of a protein called a “toxin sponge”.
Minor and colleagues recreated the genes that control the sodium channels of pitohui and poison frogs in the lab and transferred them into live cells from diverse animals exposed to BTX. The toxin killed these cells, indicating that the deadly animals’ sodium channels aren’t resistant to BTX. When scientists injected BTX onto live frogs of several kinds, only the poison frogs survived.
Minor adds, “That provides us a clue that there’s something blocking the channels from perceiving this poison.”
His main idea is a sponge protein, which he has previously found. Minor’s lab discovered a toxin sponge in 2019 that protects bullfrogs against another strong poison known as saxitoxin. Though he has yet to discover something comparable in pitohui or poison frogs, he believes it is a goal.
The findings have intrigued Rebecca Tarvin, an evolutionary scientist at the University of California, Berkeley, who has studied how poison frogs tolerate another neurotoxic called epibatidine.
“Given my area of study, I was extremely shocked to see that [poison frogs’] sodium channels are not responsive to batrachotoxin, which was not what we had predicted,” adds Tarvin, who is also a National Geographic Explorer.
However, she cautioned against extrapolating the findings too far. She explains, “This is only one of the numerous poisons that the frogs carry.” “However, I am convinced in the instance they tested.”
Toxicology research might lead to medical advances.
Though faraway island birds and rainforest frogs may appear to be a niche issue to research, understanding their biological magic may benefit people all around the world.
“Toxins have traditionally played an essential role in assisting us in identifying individual proteins and discovering their functions, as well as serving as the foundation for drug design,” adds Tarvin.
One component of bullfrog poison, for example, has been proven to have anti-cancer properties in lab testing, while the tetrodotoxin found in a variety of animals, from pufferfish to newts, has been investigated as a potential source of new anesthetic medicines.
“The most intriguing thing for me is why the hell these creatures don’t kill themselves with this toxin,” Minor adds. “However, this will also reveal something essentially significant about biological processes.”
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