Goanna venom rocks the reptile record
[ UniNews Vol. 14, No. 22
28 November - 12 December 2005 ]
Goannas and iguanas are venomous – sharing a common venomous ancestor with snakes – according to a University of Melbourne-led discovery which effectively rewrites the history of reptile evolution.
The research describes for the first time the existence of oral venom glands in goannas and iguanas and proves that venom systems in snakes and lizards evolved before the two species went on different evolutionary pathways.
Led by Dr Bryan Fry of the University’s Australian Venom Research Unit, the research was published recently in the science journal Nature.
Dr Fry says the discovery provides new insights into the evolution of the venom system in reptiles and presents a major paradigm shift in the understanding of reptile evolution.
“It not only has profound theoretical implications but also has enormous potential for drug design and development since these are venoms that have been separated for up to 200 million years from anything previously studied.”
He says it was previously believed that venom systems appeared relatively late in evolution and were restricted to the “front-fanged” snakes.
However, earlier research by Dr Fry and his colleagues revealed that venom systems were a shared trait of all advanced snakes.
Only two types of lizards, the Gila monster and Mexican bearded lizard, were known to have venom systems, but because their venom glands have a different structure to that of snakes it was assumed they evolved independently.
Dr Fry says it was thought toxic bacteria in the mouths of monitor lizards, such as the Komodo Dragon, gave them the ability to kill their prey. He and his colleagues have proved this is not the case – the lizards use venom.
Using new DNA sequence data, the researchers found nine venom toxin types that were shared between lizards and snakes. Seven of these were previously only known from snake venoms, including one that had only previously been reported in rattlesnake venom but was sequenced by the team from the Bearded Dragon, one of the most popular pet lizards in the world.
Some of the toxins had potent systemic effects, such as hypotension leading to rapid loss of consciousness or coagulation disorders which can result in prolonged bleeding.
Other non-lethal but harmful toxins dramatically increased sensitivity to pain and caused strong cramping.
“These findings force a fundamental re-thinking of the very concept of ‘non-venomous’ reptile and provides evidence regarding the role of venom in the effects produced by lizard bites,” Dr Fry says.
“We now believe that venomous function arose a single time in reptile evolution about 200 million years ago. This considerably revises previous estimates of 100 million years, when the origin of venom systems in snakes and lizards was thought to have evolved independently.”
He says the discovery of new lizard venom toxins opens additional new avenues for biomedical research and drug design.
“These molecules represent a tremendous hitherto unexplored resource not only for understanding reptile evolution but also for utilisation in drug design and development.”
The research team – already inves-tigating the medicinal potentials of some venom compounds – received an Australian Research Council Discovery Project grant worth $145,000 over three years in the latest round of ARC funding.
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