Can Domestic Selection cause Macroevolution?

Twas a mistype that's all. I meant to type 'parasitism is symbiotic'. The rest of the post is consistent with this.

Well not to split hairs, but as an ecologist and biologist myself I prefer to see the term 'symbiosis' reserved for obligate mutualisms, like the bacteria inhabiting cockroach guts that enable them to digest cellulose.I would also take issue with terming 'parasitism' any sort of mutualism or symbiosis - the benefit and flow of resources is clearly in one direction only and and there is highly negative impact in the other.

Crash and Kuresu,I want you two to have the opportunity to work through to a clear understanding, but it would be nice if you could be economical while doing it and not use up too many of the thread's 300 messages. I'll avoid putting myself in the middle by not offering any interpretations of my own, but I think if you actually put the text from Crash's Message 64 (where I think this started) in front of you that it might help:

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--	Percy
	EvC Forum Director

The only issue I might have with your example of skin color in your family is that much of it could be explained by stochastic process during development that does not have a genetic basis per se..i.e. by chance, a promoter for a specific color determining gene was turned on or off a bit earlier or later during development.But your principles are right. However, it then makes a greater case that DS is not representative of NS with respect to macroevolution. If you have to select so hard that you essentially force additive traits to become uniform, then you are effectively bottlenecking constantly to a single breeding pair in effect (which is sort of what the kennel clubs do). The selection is overwhelming. This is not a very likely scenario for most naturally occurring speciation events (calculations show much larger founder populations) and if corn is any example, then it is not likely even for many domestication scenarios..i.e. one can select for a single trait while letting others vary...or at least until breeders select for mutual incompatibility of breeds as the desired trait..then one should quickly be able to force apart two populations...seems to be what the mammal reference I cited was getting at..though I could be wrong.

But it can't. Mutualism and parasitism are two different relationships. They're very different. Right. Two different words with two different meanings. Not the same thing; just as "doctor" and "dentist" aren't the same thing. Dentists are doctors, but that doesn't mean that if you're not a dentist, you're not a doctor.Do you understand the relationship, yet? This is pretty simple logic. But that's not the statement you made, or that I told you was wrong. What you said was that if we didn't consider the relationship parasitic, we couldn't say that it was symbiosis.That's wrong. The relationship isn't parasitic, it's mutualistic; because of that the relationship is still a kind of symbiosis, even though it isn't parasitic. To tell you that there are more kinds of symbiosis than parasitism, and that when someone says "symbiosis", they don't necessarily mean to say "parasitism", as you indicated in your post. I mean let's get back to your statement:

quote:

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There's nothing symbiotic about this relationship. Unless you want to call mankind a bunch of parasites.

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In other words "the only way this relationship can be symbiotic is if we mean to say that humans are parasites."But that's not true. We can consider the relationship mutualistic, and therefore symbiotic, and therefore we have no need to refer to humans as parasites.Clear, yet? No, we didn't. I said that the relationship was mutualistic and therefore symbiotic. You said that the relationship could not be said to be symbiotic unless it was parasitic. Those aren't the same thing at all. Your statement is wrong and mine is correct.

Hi EZ,As an ecologist (but not a biologist although I play one on TV ), I also tend to separate parasitism from the other types of symbiosis when talking to other ecologists. However, the fact remains that in almost all textbooks (at least at the undergrad level) with which I'm vaguely familiar, parasitism is included under symbiosis. I think its reasonable to do so. Consider: it's often very difficult to tell whether a relationship is mutualistic or comensal - or parasitic. Think of the Acacia/Pseudomyrmex complex. Not all Acacia acacia have a mutualistic relationship with the ants. Indeed, some Pseudomyrmex species actually "take advantage" of Acacia's pro-ant adaptations without providing any reciprocal benefit. Hence the latter could be considered "parasitic" on the tree, even tho' most Pseudomyrmex species ARE obligate mutualists with them.One of the reasons I love field ecology is that things are often really complicated, and simple generalizations don't always work.ABE: Also look at the Cecropia/Azteca complex. Another example where how you define ant-plant symbiosis is dependent on the particular species - some Azteca are obligate mutualists, some are more on the lines of comensalists or even "parasites" if you figure in the energy expenditures of the tree used to provide the ants with everything from internodes for nesting sites to trichilia and mullerian bodies for food while the ants don't defend the tree at all. Just take advantage of the goodies the tree produces. Parasite, mutualist or do we need a new term?This message has been edited by Quetzal, 04-07-2006 09:22 AM

That's interesting. So, i'm guessing this is due to some sort of epistatic or maybe epigenetic effect? This is pretty much what i'm trying to get at. Its not that DS can't cause macroevolution, but that one should not use a lack of clear macroevolution in DS as support against macroevolution occurring in NS.

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"The good Christian should beware the mathematician and all those who make empty prophecies. The danger already exists that the mathematicians have made a covenant with the devil to darken the spirit and to confine man in the bonds of hell." - St. Augustine

Not necessarily epistasis or epigenetics, though both could definitely contribute. I am thinking more along the lines that even two clones may not be entirely identical. Since so much development hinges on timing of gene expression, just a chance shift in the timing or place of expression of a Hox gene for example could have large downstream morphological effects even though the underlying sequences are identical.DS is a nice example of how fast NS can work in a very extreme situation....it is also mechanistically similar i.e. bottlnecking etc. But is not analogous to macroevolution caused by NS.But it seems that creos will not understand the distinction anyway.

quote:

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not a biologist although I play one on TV

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Cool. Yes, I agree there can be a lot of gray areas.
Also most obligate symbioses probably began as parasitic relationships I know the Pseudomyrmex genus from my work in citrus and I have seen the Acacia system first hand in Mexico. Neat stuff.
My McGraw Hill Dictionary of Sci. and Tech. Terms has two very broad definitions of symbiosis. One actually says 'effects... expressed as harmful or beneficial'. So I'll have to accept parasitism as a form of symbiosis and reliquish my stand on trying to reserve it for exclusively mutually beneficial interactions, although I know it used to be taught this way a long time ago. I think this would qualify as 'cleptoparasitism' - an organism stealing resources intended for symbiont. Just like some 'nectar thieves' - insects that bore a hole in the side of the flower to extract nectar from the base, but without providing the pollination service.This message has been edited by EZscience, 04-07-2006 09:11 AM

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.

Well, I'm an ecologist, too - maybe it's a generational difference? The way I learned it, these things run along a continuum. Parasitism is not a mutualism - never said that - but a relationship can turn from mutualistic to parasitic depending on environment, such as with the Rhizobium/legume example I gave earlier (and I could give other examples, both plant and insect).Also, it doesn't have to be "highly negative" to be parasitic - just negative. There are gradients. Again, this is the way I was inculcated, less than a decade ago, so maybe it's just a matter of changing usage.This message has been edited by Belfry, 04-07-2006 10:16 AM

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.

Yes, that's my impression too.
Sort of an old-school definition I was hanging on to I guess.
(See my capitulation below)I liked your Rhizobium example.
I work in agriculture, insect ecology and IPM so I like the insect and plant examples also.
The ant-aphid mutualisms are interesting, especially considering certain species of aphid predators and parasities have evolved special adaptations to fool the ants or defend against them, including waxy secretions and chemical camoflage. All so they can get to the aphids that the ants are essentially herding like cows.I guess (to get this back on topic) one of the ways domestication is most likely to lead to macroevolution is via inadvertant side-effects on the ecology of unrelated organisms.For example, I study sunflower pests. We have changed the sunflower plant so much in domestication that it has an entirely different community of insects (all native insects, incidentally) boring into it than the wild sunflowers do, even though they are still the same species of plant. We have a longhorned borer that has become a serious pest of cultivated sunflowers and now has even colonized soybeans, and it is now really hard to find this insect in any of its original wild host plants. It is coming to specialize on crop plants exclusively - they are more nutritous and more available. I don't consider it likely to speciate any time soon, but we have inadvertantly created a very different species without necessarily precipitating a speciation event.

Ok...I just got the mental image of a dachsund trying the "splitting of the bamboo" technique I see your point. Although, and i'm going heavily anecdotal here and could be wrong, i'm sure i heard somewhere of female wolves who, when in heat, used to lure dogs into ambush. Herein lies the possibility of hybridisation. I'm basically asking whether the scientists are aiming at non-interfertility, or is it a by-product of the karyotype that they are aiming for?
I expect most of them are induced though. While chromosomal mutations are more common than single base mutations, you'd have to look at the karyotypes of a few thousand mice before you found a natural rearrangement.It can be the case that DS could bring about speciation, however, as you've alluded to, it might often require that the DS is directed toward speciation. Only then, do i feel, it would be more powerful than NS.

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"The good Christian should beware the mathematician and all those who make empty prophecies. The danger already exists that the mathematicians have made a covenant with the devil to darken the spirit and to confine man in the bonds of hell." - St. Augustine

While i did say in an earlier post to Ned, that i didn't see selection as insignificant, i'm not sure that i would go so far as to call it a key to speciation. Although, when it comes to sympatric speciation, i can see how that could be the case. Consider this possibility:
Two founder populations break off from a highly diverse ancestral population; with each accrueing a distinct subset of alleles that differs from the alleles of the other due basically to drift.
Already these populations are genetically distinct. Over enough time, with total isolation, and the accruement of new variation, it should theoretically be possible for speciation to occur. I do agree with you here. Although, the argument over which contributes more to speciation, drift or selection, has not yet been resolved in the scientific community.I would say that it is dependent on whether or not a population is subjected to strong selective pressures. If it is, then selection would be a greater driving force toward speciation. If it isn't, then possibly drift would play a greater role.

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"The good Christian should beware the mathematician and all those who make empty prophecies. The danger already exists that the mathematicians have made a covenant with the devil to darken the spirit and to confine man in the bonds of hell." - St. Augustine