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.
Ping (just in case you hadn't seen this)
lol
Not quite evolution. The red-bellied black snake and the green tree snake with larger heads have killed themselves off through eating cane toads; therefore, the snakes with the smaller heads, that can't eat the toads, are going to be the ones left to reproduce. The snakes aren't evolving. The individuals with certain characteristics are just be handed a reproductive advantage....
That's evolution. The populations of the two snake species are experiencing selective pressure from the cane toad population. As that pressure continues, the morphology of the snake populations is changing. After 20-25 generations, that change is already noticeable.
This isn't 'evolution' at all--it's patently pro-evolution lies put forth as 'science.' Bigheaded snakes can eat big poisonous things and die. Smaller specimens of the same species then survive--the 'fittest' paradoxically being the smallest and presumably weakest...although presumably also the toads are smaller when young and could be swallowed by smaller snakes. (Read "The Andromeda Strain" ...) Breeders have made miniature horses, miniature pinschers, poodles etc. by similar selective breeding. You show me a snake that can type Othello or sing Sorrento--or a dolphin that's built an underwater hospital--and I'll give a little credence to the hypothesis of evolution.
LOL
I just have to laugh at the Evotards...sorry...BWAHAHAHAHAHAHAHAHAAAAAAAAA!
Right on all counts.
Red-bellied black snakes live in the southern part of Australia. Cane toads live in the north. Regards, Byron
On another subject (not evolution):
Doesn't Australia have a long history of bringing in outside species to "solve problems", and then the outsiders themselves end up becoming a new problem?
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No more than a tendency for large busted, pretty girls to be among the first to pass on their genetics.
Cool. :-)
Yep.
http://rubens.anu.edu.au/student.projects/rabbits/wildanim.html
There are now many animals living in Australia that have been deliberately introduced to the wild. Some came by accident, others were escapees from aviaries, aquaria and zoos. They were introduced for a number of reasons that now may sound quaint or impractical. It is a good history lesson to examine past introductions so that the same mistakes are not repeated in the future.
When populations of domestic animals such as livestock or household pets become established in the wild they are called feral animals. These include the feral cats, feral pigs, the hare, feral goats, and feral horse or brumby. However, the introduced species that did not originate from domestic livestock are referred to as exotics, exotic wild animals or introduced wild animals. Here are some reasons why these wild animals from other countries were introduced into Australia and just a few example of the species involved:
Biological control - cane toad, English starling, sparrow, mosquitofish
Sport hunting - rabbit, fox, deer
Fishing - trout, carp
Practical use - ostrich, camel, buffalo
Ornamental - blackbird, song thrush
Accidental - two species of rat, house mouse, European wasp, cattle tick
Escapees - Indian Palm squirrel, goldfinch.
No, natural selection is currently taking place in the snake population of Australia.
Not insignificant, but not evolution, unless there is evidence new genes or a new species.
One also has to chuckle at the anthropomorphic "nature is taking care of itself" commentary, which sound like declarations of faith. "Nature is happening" is closer to the mark.
I wonder, what animals indigenous to Queensland that were subject to the predation of larger headed snakes might now have their populations not so efficiently controlled?
Not true. Evolution is simply the change in allele frequencies from one generation to the next. Obviously, natural selection is guiding the change, which is evolution by definition!
That's a mighty low bar. Dog breeds are examples of evolution by that definition.
Natural selection is a component of evolution, not a synonym for it.
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