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PytRons are stiTI a little^venomous NATIONAL GEOGRAPHIC^ashington, DC) 5/4/13 by Ed Yong, According to popular knowledge, venomous snakes are in the minority. Most kill their prey<brpugh other means. The pythons and boas, for example, squeeze their prey to death, constricting them in powerful coils until they can no longer breathe. But that doesn't mean they lack venom.
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Until then, everyone thought that there were only two venomous lizards—the Gila monster and the Mexican beaded lizard—which evolved their toxins independently from the hundreds of venomous snakes. Fry showed otherwise. While capturing monitor lizards in the field, he noticed that they had bulges in their heads at the same place as the Gila monster's venom glands. "It was a Captain Obvious moment," : he says.
• The Venom' glands of these constrictors .mostly pro• duce lubricating mucus, which helps the snakes to : Fry eventually isolated Venom proteins from many supposedly non-venomous species of lizard and swallow prey easily. But Bryan Fry from the University of Queensland has found that the glands still pro- snake, including all monitors and frequently kept pets duce small amounts of venom proteins. So do the . like bearded dragons and ratsnakes. He argued that » equivalent glands of iguanian lizards—the group that reptile venom evolved only once, in the common > includes iguanas, anoles and chameleons. ancestor of this reptile group, which he called Toxicofera. It covers all snakes and a significant proporThese snakes and lizards are unlikely to be using their tion of all lizards. venom to subdue prey or to defend themselves, but they clearly still make the stuff. Their toxins are the The Toxicoferan ancestor had two pairs of venom ! equivalent of a kiwi's wing or the sightless eyes of glands, one in the upper jaw and one in the lower, blind caveflsh—defunct remnants of a functional past. which secreted an already complicated set of venom proteins. Its descendents duplicated the genes that This is not the first time that Fry has shaken our un- produced these proteins, and tweaked them to proderstanding of animal toxins. In 2009, he showed that duce even more chemical weapons. They also the Komodo dragon kills its prey with venom, rather streamlined their venom glands—some venomous 10 than blood poisoning caused by a filthy bacteria-laden lizards, like the monitors and Gila monster, lost the bite. And earlier, in 2006, he showed that venom is a top pair, while the snakes downplayed the bottom set. far older and broader reptile invention than anyone had guessed. Continued on page 3
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