Formation Of New Species Proves Gradual, Not Sudden

UniSci.com ^ | 28 May 2002

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Formation Of New Species Proves Gradual, Not Sudden The formation of new species is a gradual and not a sudden process, according to a team of biologists from the UK, France, Australia and the USA. Their findings, from a study of birds on Pacific islands, are reported in today's Proceedings of the National Academy of Sciences (PNAS). The "founder effect" theory, a controversial idea among biologists, says that speciation occurs suddenly due to a small influx of colonists founding new populations, in the process creating many new gene combinations and losing many others, in what is known as a "genetic revolution." But according to the team's new evidence from fieldwork and computer modeling, the theory doesn't apply to island birds, and the way in which populations change their genetic diversity is a result of successive colonization events and long-term genetic drift. "Our results indicate that speciation in island birds occurs gradually, not suddenly as a result of island colonization through founder effects," said Dr. Sonya Clegg of Imperial College London. In order to carry out the work, Dr. Clegg and her collaborators visited a series of islands through the southwest Pacific. Dr. Clegg said: "The result is exciting because this is the first time the theory has been tested using natural populations. Previous tests have used artificially introduced ones, which don't tell you much about how real biodiversity evolves. "It's obvious that genetic changes can occur if a single pair of individuals founds a population, but the question is whether that really happens. Our results suggest that it doesn't." The scientists tested the founder effect model in an unusual island bird species, the Silvereye (Zosterops lateralis), which has colonized a series of islands in the southwest Pacific from the Australian mainland during the last 200 years. The Silvereye's pattern of colonization there was originally used to support the founder effect model, first proposed by Ernst Mayr in 1954. Though subsequently tested in lab studies and artificial populations, up until now the theory had been untested in a natural population because of the need to know the colonization date for a series of island populations. The southwest Pacific islands benefit from a well-documented history of such events, and DNA samples were taken from birds captured on the islands to be compared with samples from Silvereye colonies on the Australian mainland and with samples from island populations of Silvereyes known to be founded over 3,000 years ago. This allowed the scientists to make the crucial contrast between genetic changes in recent and old island populations. Their computer models of evolution based on these data showed that single founder effects do not lead to strong genetic changes in the Silvereye population, contrary to the founder effect model. Instead, genetic changes build up gradually -- either as a result of long-term genetic drift or through multiple bottlenecks. The authors estimate that the average successful founding flock would number more than 100 birds. Laboratory-based studies have shown that founder effect models can work, but only under very restrictive circumstances, for example, with a very small number of colonists. A natural population with known colonization dates is very rare and most studies have been done on artificially introduced populations, which limit the value of subsequent results because humans have set the size of the colonizing group. The research team included scientists from the Department of Biological Sciences and Natural Environment Research Council Centre for Population Biology, Imperial College, London; the Department of Zoology and Entomology, University of Queensland, Australia; Centre de Biologie et de Gestion des Populations, Campus International de Baillarguet, Montferrier/Lez cedex, France, and the Museum of Vertebrate Zoology, University of California, Berkeley. The Australian Research Council and the Stuart Leslie Fund (Birds Australia) funded the work. (Reference: Genetic consequences of sequential founder events by an island-colonizing bird. Authors: Sonya M. Clegg, Sandie M. Degnan, Jiro Kikkawa, Craig Moritz, Arnaud Estoup and Ian P. F. Owens. Proceedings of the National Academy of Sciences. May 28, 2002.) Related websites: Proceedings of the National Academy of Sciences (PNAS) Imperial College of Science, Technology and Medicine [Contact: Dr. Sonya Clegg, Tom Miller] 28-May-2002

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[scripter]

Ping.

[Dimensio]

This is news?

[medved]

The formation of new species is a gradual and not a sudden process, according to a team of biologists from the UK, France, Australia and the USA.

In other words, they're claiming all the evidence of the fossil record is a bunch of BS??

[pabianice]

Now we know where Liberals come from: genetic saboutage.

[Maceman]

Why does it have to be one or the other? Can't both mechanisms be acting at the same time. Is it necessary that there be only one way for species to arise?

[Cleburne]

Does it hold any portents for puncuated equilibrium? It wouldn't sound that this bit of evidence is a good boding for the late Mr. Gould's idea- if formation of species is slow, imagine the massive leap it would take for a genus or family!

[Junior]

This is news?

Dr. Clegg said: "The result is exciting because this is the first time the theory has been tested using natural populations. Previous tests have used artificially introduced ones, which don't tell you much about how real biodiversity evolves.

Now the anti-Es cannot claim that the theory has never been tested.

[Junior]

In other words, they're claiming all the evidence of the fossil record is a bunch of BS??

Huh?  The fossil record never said that speciation occurred rapidly -- that is a conclusion that some paleontologists drew from the evidence, but with which other paleontologists disagreed.  You've glommed onto part of the story and extrapolated wildly from there.

[LarryLied]

the formation of new species is a gradual and not a sudden process

Don't believe it. James Carville doesn't look like his parents at all.

[Dimensio]

No, the anti-Es will simply ignore it like they do everything else that utterly obliterates their arguments. They'll either read it and never acknowledge it, read it and point out "flaws" in the study that make it incomplete or inconclusive (flaws, mind you, that don't really exist) or they'll refuse to seek it out and thus will be able to honestly claim that they never heard of it.

The gradual nature of speciation is what I personally would expect given the nature of mutation. Now "what I expect" is certainly not a proper basis for a theory but I'd consider evidence pointing to the contrary to be a bit more newsworthy.

[Heartlander]

Formation Of New Species Proves Gradual, Not Sudden

Is there a new species?
or have they just given us the bird again...

[Dimensio]

Huh? Are you suggesting that speciation has never been observed or just asking if it hasn't been observed in this case?

[r9etb]

Now the anti-Es cannot claim that the theory has never been tested.

Well, first off one has to wonder whether even a 3000-year baseline can truly be written off as "gradual," given the time scales involved. To be perfectly honest, the article really doesn't answer the question of whether the theory of evolution has been tested, especially in the Macro sense.

All we see is a story about how they've observed "genetic changes," but we are not told their extent. We are not told if the observed changes are equivalent to the formation of races, or to the formation of entirely new, island-specific species of bird. The article's silence on the matter leads me to conclude that the differences are racial at best.

Also, what I read here tells us only about the effects of natural genetic drift and mutation for birds residing in places where conditions are probably pretty nearly identical from one island to the next. In other words, if this is evidence, it's evidence of micro-evolution.

It is not a test of the macro side of the theory, whereby entirely different kinds of animals are supposed to evolve in response to environmental pressures of one kind or another.

[Heartlander]

Speciation is indeed a real process, but speciation only means that two populations of a particular species can no longer interbreed. The two populations get separated by a geographical barrier such as a mountain range, and after a time they are no longer able to interbreed or to reproduce between themselves.
But all we have really done is split up the gene pool into two different, separate populations; if you want to call them different species, that's fine. But even Darwin's finches, although there are some changes in the shape and size of the bill, are clearly related to one another. Drosophila fruit flies on the Hawaiian Islands-- there are over 300 species--probably originated from one initial species. But they look very much the same. The primary way to distinguish them is by their mating behavior.

You say speciation, I say speculation. Let’s call the whole thing off…

[Junior]

What would be the result of accumulated genetic changes within one population, but not shared with another? If X amount of genetic changes occur in 3000 years, then how many more changes would occur in 3 million or 300 million years?

[Dimensio]

That you don't like the definition of speciation is irrelevant.

[txzman]

Man is it gonna be fun watchin' them explain their papers and thesis' to God. "Well, ya see Lord, there's no way a Supreme Being -er ....."

[PatrickHenry]

Thanks for the ping.

[Heartlander]

A Pygmy and an Eskimo… Different species?