by John Tidwell
Until recently, any biochemist who studies natural toxins would tell you that the only organisms that can create their own alkaloid poisons are plants and lower animals—nothing with a backbone, certainly. (Snake venom, an exception to the rule, is actually modified saliva protein). Toxic stars like the poison-dart frogs of South America, the pitohui (Pitohui dichrous) and blue-capped ifrita birds (Ifrita kowaldi) of New Guinea use tetrodotoxin, which they get from more primitive creatures announced at the annual meeting of the American Chemical Society last April that his team had discovered an animal that really did make its own “witch’s brew” of alkaloids.
In the alpine and semi-arid forests of southwestern Australia lives a brightly colored family of toadlets that belongs to the genus Pseudophryne. Long known to be poisonous, these toadlets are often emblazoned with black-orange or black-yellow patterns. It has been assumed that the chemical cocktail that oozed from their skin when they felt threatened was, like all others, sequestered from their crawly dinner.
In the 1980s, Daly and his team had identified the chemical structure of the toadlet’s unique alkaloids, which he dubbed pseudophyrnamines. “What puzzled us was that we never found this compound in any of the other hundreds of species of Australian frogs Working with biologists at Australia’s Adelaide University, Daly compared the skin toxins of eight wild toadlets with those of 18 that had been born in captivity and fed an alkaloid-free diet. He found that wild frogs had high levels of the same pumiliotoxin found in many Australian frog species, but only trace amounts of its own particular pseudophyrnamine alkaloids. The captive frogs, by contrast, had high levels of pseudophyrnamines, but no pumiliotoxins. This could only mean that the toadlets got their pumiliotoxins from something they ate in the wild, but they made their own pseudophyrnamines! Now Daly is studying how these pseudophyrnamines are able to block certain nerve receptors in the hope that the toxin might be useful against chronic pain and heart arrhythmias.
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ZooGoer 31(5) 2002.
Copyright 2002 Friends of the National Zoo.
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