University of Queensland, Australia, UQ NEWS, 8/22/17
Tiger snakes are part of a group that has existed for 10
million years. Credit: Stewart Macdonald
Australian tiger snakes have “hit the jackpot” because prey
cannot evolve resistance to their venom.
While that may sound foreboding, University of Queensland School of Biological Sciences expert Associate Professor Bryan
Fry said this
discovery had medical benefit for humans.
That’s because tiger snake antivenom has an extraordinary
level of cross reactivity against other snake species, and can therefore
neutralise the lethal effects on humans in snakebite cases.
“The level of conservation in the toxin sequences is not only
really unusual, but this is why the corresponding tiger snake antivenom is so
useful in treatments against bites from many Australian snakes that affect the
blood in the same way,” Dr Fry said.
“No other antivenom in the world is so spectacularly
effective against such a wide range of snakes this way and now we know why.”
Dr Fry said the research had overturned a central paradigm of
venom evolution.
“A long-held belief is that snake venom varies with diet -
that is, as the snakes evolve into new species and specialise on new prey, the
venom changes along with it,” he said.
“Our research has shown that tiger snakes and their close
relatives have toxins that are almost identical, despite this group of snakes
being almost 10 million years old.
“We worked out the reason was that the toxins target a part
of the blood clotting cascade that is almost identical across all animals.
“So we have a new addition to the theory of venom evolution;
that when the target itself is under extreme negative selection pressure
against change, then the toxins themselves are under similar such pressure.
“This is a novel twist to the chemical arms race which most
snake venoms evolve under. But it is one with direct human benefit since this
is why tiger snake antivenom is so effective against treating the effects on
the blood by quite a few other Australian snakes. No other antivenom is so
widely useful.”
Dr Fry said normally, snake venom placed pressure on the
target so that animals with some variance were more resistant to the venom,
which in turn put pressure back onto the venom for change.
“In this case, if the animals had variation in their blood
clotting proteins, they would die because they would not be able to stop
bleeding,” he said.
Dr Fry’s team studied the venom of 16 tiger snake populations
from across Australia including five island populations in the Bass Strait, and
venoms from 11 other snakes in related genera.
“This is the most comprehensive examination of this clade of
medically important snakes ever undertaken, including the first examination of
the venom of the enigmatic Lake Cronin snake from Western Australia,” he said.
“This study is a great example of the human medical benefits
that can come from studying evolution.”
The study involving researchers from UQ’s Venom Evolution
Lab, Swansea University, UK, University of Melbourne, Venom Supplies South
Australia, Snakes Harmful & Harmless, Western Australia, and the Fauna Vet
Wildlife Veterinary Consultancy, Beerwah, is published in Comparative Biochemistry
and Physiology, Part C (doi: 10.1016/j.cbpc.2017.07.005).
Media: Associate Professor Bryan Fry, bgfry@uq.edu.au, 0400 193 182 (Australia),
+61 400 193 182. Twitter: @BryanGFry
Secondary photo: Lake Cronin Snake. All photos by Stewart
Macdonald, stewart@ugmedia.com.au
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