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Evolusi racun ular berbisa yang cepat dalam pit viper  mungkin defensif ; Marsupial yang memangsa ular berbisa juga berkembang pesat

Penelitian memberikan wawasan baru tentang evolusi yang cepat di racun ular berbisa  . Penelitian molekul baru pada ular – eating  possum menunjukkan bahwa faktor  predator  ke evolusi cepat bisa ular ....read more

Rapid venom evolution in pit vipers may
be defensive; Marsupials that prey on venomous snakes also evolve rapidly

Date:

July 20, 2011

Source:

American Museum of Natural History

Summary:

Research delivers new insight about rapid toxin evolution in venomous
snakes. New molecular research on snake-eating opossums suggests that predators
factor into the rapid evolution of snake venom.

.........................

Research published recently in PLoS ONEdelivers new insight
about rapid toxin evolution in venomous snakes: pitvipers such as rattlesnakes
may be engaged in an arms race with opossums, a group of snake-eating American
marsupials.

Although some mammals have long been known to eat venomous snakes, this
fact has not been factored into previous explanations for the rapid evolution
of snake venom. Instead, snake venom is usually seen as a feeding, or trophic,
adaptation. But new molecular research on snake-eating opossums by researchers
affiliated with the American Museum of Natural History suggests that predators
factor into the rapid evolution of snake venom.

"Snake venom toxins evolve incredibly rapidly," says Robert Voss,
curator in the Department of Mammalogy at the American Museum of Natural
History. "Most herpetologists interpret this as evidence that venom in
snakes evolves because of interactions with their prey, but if that were true
you would see equally rapid evolution in toxin-targeted molecules of prey
species, which has not yet been seen. What we've found is that a venom-targeted
protein is evolving rapidly in mammals that eat snakes. That suggests that
venom has a defensive as well as a trophic role."

Several groups of mammals are known for their ability to eat venomous
snakes, including hedgehogs, mongooses, and some opossums. Opossums, which belong
to the marsupial family Didelphidae, consist of about one hundred known and
several dozen undescribed species. Most of these opossums live in Central and
South America, although there is one representative in the north that is
familiar to those who spend time outside at night: the Virginia opossum.

Some didelphids, including the Virginia opossum, are known to eat
rattlesnakes, copperheads, and some species of tropical pitvipers known as
lanceheads. All of these pitvipers have venom containing dozens of highly toxic
compounds, including many that attack blood proteins, causing massive internal
hemorrhaging in nonresistant warm-blooded prey species, mainly rodents and
birds.

The new research came out of a previous phylogenetic study of marsupials,
published as a Bulletin of the American Museum of Natural History, that
suggested unusually rapid evolution in one gene among a group of snake-eating
opossums. The rapidly evolving gene codes for von Willebrand's factor, an
important blood-clotting protein that is known to be the target of several
snake-venom toxins. The association of rapid evolution in a venom-targeted gene
among just those opossums known to eat pitvipers was the essential clue that
prompted further study.

"This finding took us by surprise," says Sharon Jansa, associate
professor in the Department of Ecology, Evolution and Behavior at the
University of Minnesota and a Museum research associate. "We sequenced
several genes -- including the one that codes for von Willebrand Factor (vWF)
-- to use in a study of opossum phylogeny. Once we started to analyze the data,
vWF was a real outlier. It was evolving much more rapidly than expected in a
group of opossums that also, as it turns out, are resistant to pitviper
venom."

The recently published research demonstrates that the rate of replacement
substitutions (nucleotide changes that result in amino-acid changes) is much
higher than the rate of silent substitutions (nucleotide changes that have no
effect on the protein) in the von Willebrand Factor gene among pitviper-eating
opossums. Typically, high rates of replacement substitutions means that the
gene is under strong, sustained natural selection. That only happens in a few
evolutionary circumstances.

"Most nucleotide substitutions have little or no effect on protein
function, but that doesn't seem to be the case with vWF in these
venom-resistant opossums," says Jansa. "The specific amino acids in
vWF that interact with toxin proteins show unexpectedly high rates of
replacement substitutions. These substitutions undoubtedly affect protein
function, suggesting that the vWF protein can no longer be attacked by these
snake toxins."

"It is so uncommon to find genes under strong positive selection, that
the exceptions are really interesting and often conform to one evolutionary
circumstance when two organisms are coevolving with each other," says
Voss. "We've known for years that venom genes evolve rapidly in snakes,
but the partner in this arms race was unknown until now. Opossums eat snakes
because they can."

The National Science Foundation funded this research.










Story Source:

The above story is based on materials provided
by American Museum of Natural History. Note:
Materials may be edited for content and length.










Journal Reference:

1.   
Sharon A. Jansa, Robert S. Voss. Adaptive Evolution of the
Venom-Targeted vWF Protein in Opossums that Eat Pitvipers. PLoS ONE,
2011; 6 (6): e20997 DOI:10.1371/journal.pone.0020997

http://www.sciencedaily.com/releases/2011/07/110718155618.htm

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