A genetic takeover on a scale never seen before among vertebrates is taking place in the western US.
An alien fish is not only hybridising with the locals, but also breaking down the genetic barriers between once-distinct species. Such multi-way hybridisation could turn out to be much more common than we thought.
Dave McDonald, an evolutionary biologist at the University of Wyoming in Laramie, and his colleagues sampled DNA from three species of fish in the Colorado river basin in the south-western US - two native species, the flannelmouth and bluehead suckers, and one introduced species, the white sucker - as well as hybrids between them.
They found that white and flannelmouth suckers breed so extensively with each other that all sorts of genetic intermediates exist; white suckers also occasionally breed with bluehead suckers.
The muttsucker proxy
The team also found another sort of fish, which they dubbed the "muttsucker" - a hybrid containing genetic material from all three original species. Since bluehead and flannelmouth suckers have never been reported to cross-breed on their own, it seems that introducing the white sucker acts as a genetic bridge to break down the barriers between these two native species
If this process continues, the gene pools of the three species could eventually merge into a single, indistinct "hybrid swarm", which may eventually pull in other native suckers as well. If so, says McDonald, "this introduced species isn't going to wipe out just one native. It's taking out a whole assemblage of native species."
McDonald's is the first published study to report solid evidence of three-way hybrids in vertebrates, says Ole Seehausen, an evolutionary ecologist at the Swiss Federal Institute for Aquatic Science and Technology in Kastanienbaum, although Seehausen says he has unpublished evidence that the many species of cichlid fish in Lake Victoria in Africa arose from a three or even four-way hybridisation in the distant past.
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Tue Jul 22 00:18:40 BST 2008 by Alan Crouch
Not ruling out coencidence?
Tue Jul 22 00:58:40 BST 2008 by Joe Lalonde
WOW...Is this not what our species is doing on this planet? Turning into one mixed hominoid.
Tue Jul 22 01:07:06 BST 2008 by Peter M
No, because we are all part of one species to begin with. There has not been enough separation for enough time between different groups of people for separate species to form.
Tue Jul 22 02:31:05 BST 2008 by Alex
If these tribrids end up being more successful, what's the big deal? Isn't that the point of evolution?
Tue Jul 22 04:05:47 BST 2008 by Dann
Exactly. If the resulting tribrids are better adapted to their environment, then they 'deserve' to prevail. It not even like the original species are becoming extinct. Their genes will continue being passed down through the generations, just with slightly different 'packaging'.
It would seem that one big omni-species with a huge amout of genetic variation would also be more likely to survive environmental change than a few individual species that are more genetically restricted. Tribridisation might actually save them in the long run.
Then again, humans can get rather fond of their abstract classification methods (and the whole notion of a 'species' is about as abstract as you can get). Some people like things to be black and white, rather than these pesky shades of grey you'll find in the 'real' world.
Tue Jul 22 08:24:50 BST 2008 by Mike
You need to see the larger picture.
The point is, what are these changes doing to the ecosystem?
Here in the UK the American signal crayfish is certainly better adapted and 'deserves to prevail', and is taking over our rivers-the problem is that it's doing it to well and the knock on effect is doing in everything from other aquatic inverts to fish fry. Even kingfisher numbers are down because they have nothing to eat.
Wed Jul 23 04:24:03 BST 2008 by Dann
Natural selection works mostly at the species level (depending on how you define 'species' of course). If there are knock-on effects of one species evolving, then that creates selective pressure on the other species that are affected, who then either adapt or die in their own right.
Ecosystems are always performing a delicate balancing act, so you can't really 'destroy' an ecosystem; you really just alter the balance in some way. Some species might become extinct in the short term, but life in general tends to find new balances. It's a pity for those species that can't adapt quickly enough, but those that manage to survive become better for it.
The only constant in life is change. Sometimes that change is of the catastrophic type, but life in general has already proven robust enough to survive for several billion years.
Or am I now looking at *too large* a picture? :)
Tue Jul 22 19:27:59 BST 2008 by Christopher Wininger
Its all just nature unless you want to survive. Youre right, this is just evolution in action and nature doesnt care. The only problem is that this affects our food supply and the balance of our ecosystem. Of course we can just stand back and watch it happen and that would be fine for nature. Its just that all the changes are taking place so fast that it may not be fine for us. Despite being so prevalent it is my belief that we are a relatively delicate species. We sit high on the food change and depend on other animals to pre-process our food. We are relatively large and consume a lot of food and without the help of other large life forms (fur, wood, etc...) we do not fair well outside of a narrow temperature range. All it takes are a series of small changes and we could be wiped out. During past extinctions it has been the large dominant species that get knocked off. The dinosaurs were toast but small mammals and insects survived. Lets get it straight we are not trying to preserver species diversity, global temperatures, and coral reefs to save the planet. The planet will be here. It is us we are trying to save.
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