Worth watching.
Posted on 12/11/2004 11:50:10 PM PST by snarks_when_bored
The toads ( Bufo marinus ) were only introduced in the 1930s but have already overwhelmed the local wildlife in Queensland with their rapid reproduction and toxic flesh, which kills many predators foolish enough to make them a meal.
But for two species of snake, at least, natural selection has produced a defence: the snakes have developed relatively smaller heads and longer bodies.
In essence, the reduced gape of the animals limits their ability to eat the toads likely to do them the most damage.
| It's nice to see that Nature's looking after itself Dr. Ben Phillips, University of Sydney |
"We've got large lizards, such as monitor lizards, that seem to die after eating cane toads; a lot of our snakes after eating them will die," explained Dr Ben Phillips, of the University of Sydney.
"All the native frog-eating creatures in Australia, and the native cat that we have, are disappearing quite dramatically from areas where cane toads are turning up," he told the BBC World Service's Science In Action programme.
"Basically, large predators that would normally eat frogs are succumbing to cane toads quite dramatically."
Quick adaptation
The cane toad was introduced in 1935 to help control a crop pest, but has since become a nuisance itself.
Its range in Queensland has steadily expanded and the toad is now moving into New South Wales and the Northern Territory.
The way the two species of snake have adapted to cope with this challenge has been described as a classic example of "contemporary evolution".
The red-bellied black snake ( Pseudechis porphyriacus ) and the green tree snake ( Dendrelaphis punctulatus ) are highly susceptible to toad toxins.
And the presence of Bufo marinus has imposed an immense selection pressure on their populations.
"One of the ways the snakes seem to be fighting back is by changing their body shape. Basically, their heads have got smaller relative to their bodies (or their bodies have got bigger relative to their heads; whichever way you want to think about it)," said Dr Phillips.
"If a snake's got a small head, it's going to be able to eat a much smaller prey item."
"What that means is that because snakes eat their prey whole and the size of meal is entirely dependent on the size of its head; if a snake's got a small head, it's only going to be able to eat a small prey item.
"Thus, it's going to be able to poison itself a lot less effectively on a cane toad - which is probably a good thing, given that they seem to be a little bit silly about eating things that taste bad."
Natural selection ensures these are the snakes that prosper and reproduce; their head-body traits come to dominate populations.
Alien response
What seems remarkable is that this adaptation has occurred in just 70 years. But Dr Phillips says it should not be too surprising since snakes breed comparatively quickly.
"We need to remember that snakes have a generation time of two or three years; so basically that means a time of 20 to 25 generations has passed since the cane toads arrived in some areas," he said.
"That's a reasonable amount of time, evolutionarily speaking."
The University of Sydney researcher commented that it was encouraging to see that ecosystems could respond to problems imposed by invasive species.
"I think it's a bad idea to leave species around the place - it's almost impossible to know what kind of impact they will have," he said.
"But the upside of what we have found is that while it's all doom and gloom about the environment - we hear a lot of bad news - it's nice to see that Nature's looking after itself."
Dr Phillips and his colleague Dr Richard Shine published their work in a recent edition of the journal Proceedings of the National Academy of Sciences.
So, are the dead snakes reproducing?
Or, are other snakes watching and telling their babies not to grow such big mouths?
"evolution" my a$$!
LOL! Then why not just point to the allele frequencies of dog breeds as examples of evolution and be done with it?
Natural selection is not a synonym for evolution, it is a component of it, just as a tire is not a synonym for a car, but a component of it.
Demonstrating natural selection is an important part of demonstrating evolution, but showing me a tire is not the same as showing me a car.
The distribution of alleles is shifting dramatically in the overall population. Buy a clue, that's evolution is!
Your explanation sounds like 'survival of the fittest'. How is it different?
I won't touch that comment.
Worth watching.
Actually, the cane toads have killed off most of the red-bellies in the north. It's still found in northern Queensland, although its numbers are dwindling.
Exactly. Why is that even when people accept the facts, they can't accept the truth of the larger propositions which naturally derive from them? It's an attitude that reminds of the libs who concede, yeah, the Taliban and the Baathists were awful, and yeah, we have all the evidence that they did awful things, and yeah, they are a threat to world security, BUT THAT DOESN'T JUSTIFY STOPPING THEM!
Evolution has as much to do with the least fit organisms not reproducing as it does with the fittest surviving. The snakes which are dying before they can reproduce, or at least bear a large enough number of offspring to pass their genes on to, are those which are least fit to adapt to this intruder-species in their mist. Those which are surviving and are able to reproduce quickly enough are those who have features-be they smaller heads, greater resistance to poison, or whatnot-which allows them to better cope with the invaders.
Must have been asleep during that class.... ;^)
No, because the snakes aren't giving birth to frogs, as per creationist evolution.
I don't care what changes have happened to those snakes, they are STILL SNAKES.
Ah, new discovery.
"Extinction proof of evolution!"
Glad to hear we can quit wasting time and money protecting "endangered species".
It would be more accurate to say that extinction is explained by evolution.
Glad to hear we can quit wasting time and money protecting "endangered species".
On the contrary, understanding how species evolve and adapt has allowed for improved wildlife conservation, and a better understanding of which species are truly at risk. If more people on both side of the aisle actually took the time to understand evolution (and basic economics), the "land rights vs. the environment" debate would be considerably less acrimonious.
Cheers, Byron
I won't touch that comment.
Especially coming from 'Down Under' what is that #@$&%!! stuff called, marmite or vegemite or whatever? ;-)
Thanks for the ping!
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