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Does gene flow really support Darwinian speciation?


Apparently not:

Spatial isolation is known to promote speciation — but researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich have now shown that, at least in yeast, the opposite is also true. New ecological variants can also evolve within thoroughly mixed populations.

The idea that speciation is based on the selection of variants that are better adapted to the local environmental conditions is at the heart of Charles Darwin’s theory of the origin of species — and it is now known to be a central component of biological evolution, and thus of biodiversity. Geographic isolation of populations is often regarded as a necessary condition for ecotypes to diverge and eventually form new species. When populations of a given species are separated by geographic barriers, favorable mutations that emerge in either can become fixed locally, as mating between the two populations is precluded. Whether or not speciation can occur under conditions in which gene flow between two populations is possible — such that genetic mixing can still occur — remains controversial. In order to resolve the issue, LMU evolutionary biologist Jochen Wolf and his group in cooperation with Simone Immler (University of East Anglia, UK) have used baker’s yeast as a model system to experimentally explore what happens when the degree of gene flow between genetically differentiated populations is gradually increased.

Ludwig-Maximilians-Universität München, “Evolution: Speciation in the presence of gene flow” at ScienceDaily

Their results don’t seem to have supported classical Darwinism but they have a really hard time explaining that.

The paper is paywalled.

See also: A physicist looks at biology’s problem of “speciation” in humans

I just noticed a thread here that picks up the tenor of my comments above. "News" has titled it: "Now, Organisms Engineer Their Own Evolution." Solutions to common problems are built into the genome. The genome then "uses" nature (NS+RM, if you will) to work out a quick solution to the presenting problem and then it settles back into what it usually does. But this is essentially "Darwinian Evolution" on the time-scale of hours and days, not millions of years. This means that NS+RM applies "locally," but not "globally," and the problems about evolutionary trees that's taking place elsewhere confirms this "local, but not global" aspect of NS+RM. This renders Darwinian evolution trivial. From the thread: Evolving populations are less like zombie mountaineers mindlessly climbing adaptive peaks, and more like industrious landscape designers, equipped with digging and building apparatuses, remodelling the topography to their own ends. PaV
More to the point, what was the nature of those many mutations? Did any of them add information to the genome? Or were they all degraded or deleted genetic code? As was shown about Lenski's long-term evolution experiment, the E-coli that "evolved" to grow faster did so by jettisoning genetic info they did not need in that experimental environment. This is just as Michael Behe says in his book "Darwn Devolves". It would be interesting for someone to examine the changes in the "specialist" population, compare them with the known functions of the genes in the "generalist" or wild population and see if some of those functions are shut off or no longer work. You can be certain that, had they found an actual new function, based on added new genetic code, they would be publishing everywhere their "proof" of Darwinian evolution, and every science magazine would be lining up to interview them, for front page stories. The fact this has not happened suggests that nothing new was found - only the same old broken or disable genes that always occur. Fasteddious
A little discussion of this PR may be of interest to some: "But to our surprise, when the populations had been thoroughly mixed over time, we found very marked differences in phenotype," says Wolf. "When the tap is turned on fully, so to speak, one suddenly finds that mixtures contain two distinct variants, a generalist and a specialist." The generalist can survive equally well in the top or bottom compartment. This is not true of the specialist. But it divides at a faster rate than the generalist, and can therefore compensate for its lack of versatility. In Wolf's view, the emergence of these two classes can be regarded as the first step in a speciation process which takes place in the presence of maximal gene flow. Notice here that what allows the "specialist" variant to survive is that it's reproductive rate has changed. But why didn't the "generalist's" rate change? It seems this yeast knows that this should be happening. But, how does it "know." Let's go on. In addition to these phenotypic results, the team characterized the full genetic inventory of all populations. These genetic experiments show that adaptation to top and bottom compartments in the absence of gene flow is accompanied by the selection of genetic variants from among those that were already present in the progenitor population. In contrast, the emergence of specialist lineages in 50:50 mixtures is attributable to newly acquired mutations. And such mutations are obviously not in short supply: "The mutations seen in our replicates are completely independent. We very seldom see the same mutation in different samples -- yet the phenotypic division between generalists and specialists in completely mixed populations has been observed repeatedly," Wolf says. Notice that this time it's NOT the "reproduction rate" that's changed, but the "mutation rate." But why? It seems like the organism again "knows" that it needs to mutate rapidly if it is going to find the 'right' mutation to adapt to the new niche. But what is telling it to do this? Well, isn't it obvious that the organism (and one would suspect all eukaryotes along with it) has a "program" designed to deal with these kinds of situations. But who "wrote" the "program"? How does this yeast population know that these "specialist" cells should make completely 'random' mutations? I think it is reasonable to understand what we're seeing as the organism (yeast, here) changing its character and changing its reproduction rate and mutation rate in order to "adapt" to the niches that exist in its environment. Which leads to the following conclusion of the PR: These results are of significance in the context of how populations react to alterations in the character and distribution of variable niches. "It has always been assumed that interruption of gene flow is a prerequisite for adaptive divergence," says Wolf. "But our study shows that, even when populations are highly connected, diverse adaptations can nevertheless emerge, such that all available niches can be filled." So, think here of "punctuated equilibria," or "neutral theory." We're seeing that gene flow interruption doesn't necessarily lay the foundation for mutation to arise and become fixed in the population. Here, despite high gene flow (50:50 mixing of populations) between these separate populations, i.e., 'generalist' and 'specialist,' an abundance of mutations arose. That's not what the theory expects. It looks like the organism has all the "information" it needs to 'adapt' to the new 'niches.' Where did this information come from? How COULD it evolve since evolutionary theory expects the OPPOSITE of what we see? PaV

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