Domestic Animal Breeding and Speciation

Reading from the article, they had a tough time even conceiving, and then the mother wouldn’t even feed them. For all intents and purposes, they would be separate species if found in the wild.

I found another interesting reference:

"These were dogs with family lines, where they routinely produce big litters, and yet when we tried to breed these fertile beagles to fertile setters, we got no pups at all, despite many attempts to do so, and then eventually, we were able to produce one litter with two pups in it."
http://sciencenetlinks.com/science-news/science-updates/dog-breeds/

So there are instances where dog breeders have had difficulty hybridizing dog breeds, and I suspect that this isn’t an isolated case. The simple act of inbreeding concentrates and fixes rare lethal recessive traits that can cause a lot of problems.

@T_aquaticus, I am sorry to report that that article now appears highly dubious!

Wikipedia has a pretty fascinating article on dog evolution, and I don’t think the case has been settled yet. It cites two sources (from 2015 and 2016) that say that although dogs are descended from an extinct subpopulation of gray wolves, they are more closely related to European gray wolves than to North American wolves. So, still considered the same species, especially considering interbreeding has not been rare.

http://m.genome.cshlp.org/content/26/2/163

And this one:

Thank you, @beaglelady. I figured we would successfully arrive full circle (from post 26) … and be all the more convinced because of the effort to do so:

Another Way to Conclude?:
As to the general question of Speciation in the world’s population of domesticated dogs … maybe the quickest and least controversial way to express my position is that if the domesticated dog is already highly inbred, it becomes intuitively likely that it takes longer to speciate from a state of “highly inbred genetics” - - compared to speciating within a population that is the opposite of “highly inbred”.

Now that is a discovery!!!

As far as anecdotal information goes, that is pretty interesting. But we need to have a genetic test to go with that result!

Did the Beagle and Setter share the same lethal recessive trait? Or was there something else more complex going on?

Good find, @T_aquaticus !!!

Wait, what? Why do you think that? It seems to me inbreeding is likely to create more opportunities, not fewer, for populations to become reproductively isolated, especially when the inbreeding is being forced by humans who can alter selective pressures.

But there’s a bigger point I want to make here: this entire discussion, while interesting, seems to take for granted the existence of a well-defined process called “speciation.” For the most part it seems that the conversation is really about reproductive isolation, which should not (IMO) be equated with “speciation.”

My view is that “speciation” is a topic/process in the way that “mountain formation” and “reproduction” are topics/processes. We don’t talk about “mountain formation” or “reproduction” as though either one is a singular process; we know that both occur in various and disparate ways, and we are comfortable with uncertainty and even some vagueness about whether and when it has actually happened. I recommend the same intellectual stance toward “speciation.”

This review article from TREE in 2011 might help readers see what I mean. There are dozens of questions gathered under “speciation,” and some of them don’t even seem to be “good questions” anymore. Contact me offline for a copy if you don’t have access. :slight_smile:

http://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(11)00261-8

Here’s the final sentences:
“Arguably, every speciation event is unique. The common ground cannot be found by trying to force these events into categories, but it might be reached by focusing on the evolutionary forces, ecological circumstances and genetic mechanisms that they share. We are better placed now than ever before to move from a narrow perspective of speciation biology based on a handful of organisms and really start taking advantage of the endless forms of developing species. The biology of speciation can now enter a new era.”

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I think I can agree with you on this…I would say that despite the phenotypic diversity of dogs, their genotypic diversity is surprisingly low and makes them unlikely to produce new species anytime soon. However, since their population size has grown much vaster than the gray wolf’s, their genetic variance is probably increasing faster and in the very distant future, new species of dog are perhaps more likely based on these conditions.

Why do you think that speciation and genetic diversity are so closely related? I don’t know of any data or analysis that has concluded this. Do you?

It was the best reason I could think of why Chihuahuas and Great Danes aren’t considered separate species despite inability to breed with each other. How would you put it?

I would say that “inability to breed with each other” is not speciation. My understanding of this inability to mate is a mundane result of physical anatomical limitations. Yes, that’s a prezygotic barrier, but not a very interesting one, and definitely not sufficient to be called “speciation.”

But my question was about why you linked genetic variance and speciation. I don’t think those two things are closely related, and I can picture it going either way: a population that loses substantial genetic diversity via inbreeding (for example) could become reproductively isolated via fixation of alleles that would create barriers. I haven’t seen analysis of this question, but it’s a busy day and I haven’t looked.

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I would have to agree with you, @sfmatheson, if one started a chapter on speciation by simply asking if the two populations in question “could breed”. There could be any number of reasons why successful breeding fails between two animals.

The more precise phrase which I have used quite frequently is: “Genetic Reproductive Compatibility”. This cumbersome phrase is an attempt to focus the reader’s attention on the question of “genetic compatibility”, not just any reason that might block the production of the next generation.

And certainly, what is intended in the discussion is no more and no less than how Ernst Mayer intended it:

"Although Charles Darwin and others posited that multiple species could evolve from a single common ancestor, the mechanism by which this occurred was not understood, creating the species problem. Ernst Mayr approached the problem with a new definition for species."

In his book Systematics and the Origin of Species (1942) he wrote that a species is not just a group of morphologically similar individuals, but a group that can breed only among themselves, excluding all others.

“When populations within a species become isolated by geography, feeding strategy, mate choice, or other means, they may start to differ from other populations through genetic drift and natural selection, and over time may evolve into new species. The most significant and rapid genetic reorganization occurs in extremely small populations that have been isolated (as on islands).”

In the scientific literature, the initial stages of reproductive isolation and beginnings of genetic divergence is often called “incipient speciation”. I think that is a good way of dealing with it since speciation is a continuum and not a quantum leap.

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I suppose it’s because genetic variance is one half of the two main drivers of evolution, with selection being the other one. And dogs are the classic example of application of artificial selection, sometimes to extremes, and I’ve heard non-experts wonder before why this hasn’t produced speciation before now. My response, also as a non-expert but with a more than passing interest in dogs, has been to refer to insufficient genetic variance.

But I’m sure it could be phrased much better than my poor efforts, and I’m open to correction if I’m wrong.

There’s also the side issue of how inbreeding due to reduced population in gray wolves compares to inbreeding due to purebreed mania in dogs, and the effect it will have on future generations and centuries of canines assuming things keep going as they are, as well as the effect to be expected from dogs being the most numerous large carnivore on the planet and therefore having increased chances of sometime having very beneficial mutations pop up. I was trying to condense too much into what I said, I think.

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Languages are usually a good analogy. Let’s take all English speakers and divide them up between 2,000 planets where they can’t talk or write to each other. After 2 years they could probably come back together and understand each other just fine, or at least as well as they did before they split up. However, if you kept them apart for 1,000 years you might see the emergence of new languages on each planet, and they would be different enough from one another that they couldn’t understand each other if the different planets were brought back together.

It takes time for new changes to build up in each language before they diverge enough to be a new language. Simply isolating them from one another, which is what dog breeding does, is not enough. You need the accumulation of changes on top of changes in order to see a real difference, and that takes time.

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The answer, in my view, should begin by saying that selection and speciation are simply different topics. If there is any one necessary component in speciation, it’s separation not selection. The fact that dogs and teosinte have experienced intense selection, leading to intense morphological change, is simply unrelated to the question of whether the altered populations are (or could be) isolated enough to diverge toward “speciation.” One way to see this is to consider examples of instantaneous “speciation,” in which reproductive isolation occurs overnight. These examples don’t involve selection at all. Any relevant selection occurs after the fact of isolation.

So, why are there no dog breeds that have become reproductively isolated? (I’m assuming that is true; it might not be.) The most reasonable hypothesis, to me at this point, is that the selected traits haven’t affected reproductive function in such a way as to lead to reproductive isolation. Would it be possible to select for traits that would? Yes, I think so, and perhaps this has happened repeatedly (accidentally) and the results discarded.

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That’s a reasonable generalization, but we know of counterexamples. It’s true that mere separation can’t induce speciation by itself, and it’s true that the accumulation of change in two isolated populations can result in speciation. But reproductive isolation can occur extremely rapidly, and in fact that is a main focus of studies of “speciation genes.” I don’t know if we have examples of isolated populations NOT speciating after millions of years, but we do have the converse: reproductive isolation arising overnight.

I would love to read some of the literature on that, @sfmatheson.

I had not heard of cases like that!

From a few months ago:

Yes, this is what I was trying to say, only much clearer! It’s why I specified “very distant,” at any rate.

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