Can Domestic Selection cause Macroevolution?

Hey Cookie.I've argued before, so I might as well argue now, that dog breeds are a ring species. That is, certain breeds are reproductively isolated from one another (in a pre-mating sense), except for the fact that genetic flow could occur between them using other breeds.If all domestic dogs except for dachsunds and saint-bernards were wiped off the face of the planet, the remaining dachsunds and saint-bernards would represent two species because of pre-mating reproductive isolation. In absence of human intervention, I don't see the two breeds as being reproductively compatible.So... this doesn't mean "dog breed speciation" has happened as a result of artificial selection, but I think it shows artificial selection could produce such distinct creatures from a common ancestor as to be morphologically/behaviorally incompatible for reproduction.Another example that comes to mind is mice that are selected for karyotype abnormalities by genetics laboratories. Mice bred to homozygosity for the novel, "abnormal" karyotype, even though happy, healthy, and fertile, are no longer interfertile with mice with the original "normal" karyotype. It is important to note that these karyotype-level mutational changes do occur naturally, (though they have also been induced). This is an example of artificial selection producing two populations of mice that are post-mating reproductively isolated (speciated) from one ancestor population.

Some points on this:- I would consider the previously mentioned example as a case of human intervention. The really small and really large dogs were raised by humans to tolerate one another. Those same dogs, if feral, would likely avoid one another, perhaps be in a predator-prey relationship; but overall, I doubt a large feral female would let a tiny feral guy get up in her business. (But who really knows - there's a lot of if and hypotheticals I'm throwing around...)- I'm not sure of the breeds involved in your example, but there may be two breeds that simply could not mate based on morphology - there may be no position that allows for successful copulation. I looked a bit on-line to see if anyone had identified two breeds that could not mate, but didn't find anything.- Species designations allow rare hybridization events. Some species of the Galapagos finches, for example, produce hybrids. The species barrier will only break down if the hybrids are equally or more fit than the parent species (which may likely be the case for dachsunds and saint-bernards).Again, the dog argument is obviously hypothetical - but like you mention, it does demonstrate the variety that can be produced by natural selection. It may be that if dog breeders select for reproductive incompatibility, it could be achieved, though it doesn't seem like a very desirable trait. (For example, if a tiny breed was selectively bred for small penis size, it may be able to continue to copulate successfully with its own breed, but have issues with a much larger breed). Not sure what you mean, but these are naturally occurring mutations (though a process that can be accelerated in the lab). Speciation events have occurred in the wild in mice based on chromosomal rearrangements/translocations. The source of the mutation isn't necessarily different, though the means of selection is.In the case of those occurring in the lab (sometimes naturally, sometimes induced), when such a rearrangement is found, it is humans that selectively fix the new "mutant" karyotype to insure that it is maintained. In nature, fixation of the new karyotype relies on natural selection, or simply chance assortment to fixation in small populations. Either way, in some cases, mice with the new and original karyotypes are no longer interfertile.Actually, similar translocations occur in humans more often than you might think. In a mad-scientist scenario involving incestuous eugenics, a new species of humans could be selectively bred that was no longer interfertile with humans with the old-school karyotype.At the level of fixing chromosomal rearrangements to produce inter-population sterility, it would seem artificial selection is more powerful that natural selection in creating a speciation event.

Selection still appears to be the key, especially since there's been a few cases of sympatric speciation reported.Really, in the majority of cases, both are likely necessary. Separation of one population into two is generally not going to result in divergence to speciation unless the two populations face different selective pressures following isolation.

Scientists aren't aiming for anything. They are maintaining naturally-occurring mutations for various reasons. A few thousand mice is nothing, though, in the world of mass-production and highthroughput mouse genetics. The Jackson Lab, for example, has a few thousand different lines of mice actively breeding - I'm guessing at least a few thousand mice are born every day in their facility.Besides, many mutations are found because they produce abnormal phenotypes, which are particularly obvious in homogeneous inbred mouse strains. No detailed genetic testing needed. Not sure of the ratio of induced to natural. But, that doesn't really matter for the question that serves as the topic title. What does matter is that humans selectively bred natural variation within one population to produce two populations that are no longer interfertile. Thus, artificial selection can produce speciation.

Yes, drift could potentially result in speciation, which is why I said "generally" different selective pressures would be required. The accruement of intergroup variation is going to be stochastic and relatively much slower in the absence of selection. If both groups stay under strong normalizing selection, variation will be kept at a minimum (selection would maintain them as a single species).There is at least one example of a species with populations that have been isolated since Pangea split into continents (some sort of lettuce-like plant?), but remain one species - despite an enormous time of isolation (and drift). On the other hand, there are cases of explosive sympatric speciation of hundreds of fish species occurring in the past million years or so in the African rift lakes - I would argue under very strong selection, and largely without isolation events.I guess my overall point is that I don't see the point in trying to rank processes like isolation, selection, and drift when it comes to their contribution to speciation.

Absolutely, sorry if I misread you. It had seemed to me that you were trying to rank them in a general sense that would apply to all speciation events; now I see you are referring to understanding specific instances - which I take no issue with.

It doesn't have to be direct, and I didn't mean to imply such. Selection for other phenotypes can indirectly, and readily, cause reproductive isolation. Doesn't follow for me from your previous statement.Selection that indirectly alters reproductive compatibility is still selection, not drift. Selective forces that differ between the two niches that the two isolated populations inhabit will cause divergent evolution between those populations.And, as in my comments to Cookie above, I think it is a mistake to make generalized comments about the processes involved during speciation.