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Monitoring goanna venoms


 
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Dr Bryan Grieg Fry looks at the venomous side of Australia’s large lizards, which has been largely overlooked compared to snakes.    
The reptile anatomy books don't show it but all of Australia's goannas have large venom glands running the length of their jaws. The oversight was probably due to the fact that no one had died from a goanna bite. Apart from the venoms being less toxic than those of some of snakes, the venom delivery is also not as efficient as a snakebite which is like being injected by two hypodermic syringes. Goannas have large venom ducts near the base of their teeth, so the venom must be chewed into the prey, a far slower process. Why do such powerful predators as goannas even need to resort to venoms when they are well armed with large claws and teeth? Basically, it provides an added advantage in that helps incapacitate the prey for example by prolonging bleeding or causing intense pain.

 

 
Toxin ecology is part of a complex chemical arms race, with many being incredibly potent and incredibly specific. Complex venoms, such as those in goannas have lots of different toxin types being produced simultaneously, each more toxic to a different kind of prey item - for example birds, small mammals or fish. This means that these generalist predators have a smorgasbord of toxins that work on their wide range of prey. This contrasts with streamlined venoms, such as those of sea snakes, which are targeted towards their one kind of prey, fish.

 

 
But venom production has a high energy cost. Just joining one amino acid to another takes four molecules of adenosine triphosphate (ATP), the power molecule in all our biochemical processes, so making a long protein (such as in a venom) is an energy-sapping process. Since it is such an energy intensive process it must provide a survival advantage for a species since energy used to make venoms is not available for other 'survival of the fittest' functions such as rapid growth to sexual maturity and continuation of the species and for some species it has been a case of use it or lose it. Some species of sea snakes for example which gradually changed their prey from fish to fish eggs some 5000 years ago, have (in this short period in evolutionary terms) virtually lost their venom delivery system and potency is about one percent of related species of sea snakes that continue to prey on fish.

Photos from Bryan Grieg Fry and Tally Palmer
Text: V.B. October 2008


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Adding up the toxins Australian snakes - very venomous but so few deaths

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