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Snakes and lizards share venom, evolutionary history,
study finds
Nov. 16, 2005
Courtesy Nature
and World Science staff
Conventional wisdom has it that, among reptiles, venom delivery is
mainly associated with snakes, and that it underlies their dramatic evolutionary success:
2,500 out of 3,000 snake species are poisonous.
In contrast, venom delivery is found in just two lizard species, in which it is
thought to have evolved independently from snakes.
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The Gila Monster, one of two species of
lizards known to be poisonous. It is not aggressive and must actually chew on its victim to inject its poison,
which is seldom fatal to humans. (Artist's impression, courtesy U.S. Dept.
of the Interior Bureau of Land Management)
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But a new study by Bryan Fry of the University of Melbourne, Australia, and
colleagues has found that that venom delivery among lizards
may be much more widespread.
The researchers said they showed that members of two additional lizard lineages
also produce and can deliver venom toxins. The lineages
include Monitor Lizards and Eastern Bearded Dragons, a popular pet.
The new work suggests the side-effects of nasty lizard bites may actually be due to venom rather than incidental bacterial infection,
as was previously thought, Fry and colleagues asserted.
Also, they said, the findings suggest snakes and lizards are much more closely related than has been previously
believed. Snakes evolved from relatively advanced lizards, they
suggested, rather than being a separate branch on the evolutionary tree.
The study is to be published online by
the research journal Nature this week.
Among living reptile species, only the Gila Monster and Beaded Lizard were
previously known to be poisonous, the researchers wrote. They claimed to have
found toxins in four Monitor species and the Eastern Bearded Dragon.
A new genetic analysis shows that all lineages that can deliver toxins share a common ancestor, they
claimed. This demonstrates “a single early origin of the venom system in lizards and
snakes,” probably about 200 million years ago, they said, during the dinosaur era.
The research opens new avenues for drug development based on still unknown molecules found in lizard venom, they added.
“These molecules represent a tremendous hitherto unexplored resource not only for understanding reptile evolution but also for use in drug design and
development,” they wrote.
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