Domestic Animal Breeding and Speciation

Faith & Science Conversation
21

@Lynn_Munter,

I’m not sure your hypothetical relates well to the topic I’m discussing.

For example, the topic of Ring Species frequently deals with populations of animals advancing into territory (or continuing to hold territory) that bends around a natural barrier (say, a mountain, or a bay).

The exchange of genetic material is summarized at the population level, rather than at the ultimate range of a single individual.

I’m sure there is a fancy field of mathematics that would help visualize this. But essentially the exchange of genetic information is between members of a subgroup that are closer to each other than is the distance between neighboring subgroups.

In an extended range that circles around mountain, or a canyon, or body of water, intra-subgroup exchange is high, while inter-subgroup exchange is low. And should an average individual from one of the the two terminal ends of the entire chain of subgroups attempt to mate with an average individual from the other terminal end of the range… mathematically we would expect there to be less reproductive compatibility, simply because the effects of genetic drift become that much more significant than the amount of genetic exchange (which could still be going on at a low level) between the two terminal subgroups.

In view of this description, I think you can see, @Lynn_Munter, that the lone wolf scenario is perfectly fine - - just not applicable to the question at hand.

As to the “exuberant crossbreeding campaigns” that I mention… let me provide a rough image of how I visualize the matter… it is far from complete… but it is the start of a master chart representing approximately 525 million dogs believed to be living on Earth today, divided into 339 Breeds, aggregated into 10 major categories of Breeds (as recognized by the World Canine Organization, and leaving all else as either Mutts or Cur), and 60 Regional Types.

In the picture below, the X Axis is 2 regional types x 30 columns, while the Y Axis has 10 rows for the categories and an 11th row for Mutts/Cur. This visualization may turn out to be a dead end. But what I will hope to show with it is that generations of Breeding programs, overlapping various chunks of breeds and regions, over time, should well have touched every obscure kind of domestic dog one can imagine.

Even though a breeder is trying to restrict the genetic scope of his breed, that is only after the breed is established. To build a breed, sometimes the breeder has to bring in genetic contributors from another chunk of the domesticated dog population.

Then there are the dogs that don’t make the cut. Does he euthanize them? Or does he give them away? Over centuries of time, I’m thinking all this activity is more like a Cuisinart blender at the Mutt-End of the spectrum, with the ultimate result being a very robust reproductive compatibility between the various corners of the dog population - - rather than a pattern of dogs that are not able to breed well with each other (setting aside obvious physical limitations like giant Greyhounds vs. Corgies).

Anecdotally, at the very least, I have never heard of any dog lover or dog breeder talking about how some breeds just can’t produce pups… which would be a “flag” that there are pockets of reproductive incompatibility.

525-Million-Domesticated-Dogs.jpg980×539 222 KB

22

Yep… agreed.

But in the specific discussion, setting aside those occasions when a behavioral novelty suddenly splits a population, we are looking at the “genetic machinery” that tries to create a fertile generation of off-spring, but fails to do so.

What is happening in the uterus after a horse and a donkey mate? I can only presume there are multiple ways for the formation of a fertile offpsring to fail. But most of us don’t even know one of the ways 2 sets of chromosomes fail to pass the test!

And once the “typical” genetic configuration of one population is no longer compatible with the configuration of another population, we have speciation.

Until we have speciation, we are very unlikely to find a population that diverges into some dramatic new direction of its phenotype.

23

If it sounded like a hypothetical, it shouldn’t have. Wolves routinely do travel thousands of miles and mate with other subspecies of wolf.

24

I think this article does a good job of explaining the genetics of the horse/donkey hybrid known as the mule.

So why would anybody want a mule since they can’t have offspring? Well, mules are as large as horses, but are much stronger. They are also smarter and more sure-footed. And they can have great personalities. Their strength made them important in doing farm work–they make great draft animals. Today they carry visitors down the Grand Canyon. (That’s on my bucket list.) George Washington (that other George) took a very keen interest in mules after learning of their qualities.

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One of the most interesting experiments in animal domestication was conducted by Russian geneticist Dmitry K. Belyaev. He was trying to create a domesticated silver fox. Because Lysenkoism was in favor at the time, Belyaev lost his job, but continued his experiments undercover. Belyaev also created a line of very aggressive foxes, but that fact is little known.

For more information, see the online course Dog Emotion and Cognition

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@Lynn_Munter,

I didn’t intend the term “hypothetical” to mean I was skeptical that wolves have a tremendous range.

My point was more that I had no “skin” in the topic of wolves. I’m sure wolves, like predator species everywhere, make for a solid example of “speciation”. But bringing up wolves, when I’m discussing the unique characteristics of a non-wild (i.e., domesticated) animal population heavily manipulated by humans, doesn’t seem to send us in any particular direction.

My discussion is focusing on a good answer to those who think the domesticated dog population should be some sort of epi-center for speciation … when it appears that Canine lupus familiaris is not a good candidate for spinning off species like a breeding female dropping puppies.

Reading through the Wiki article, I now wonder if dogs may have evolved a particular sensitivity to in-breeding, that defends the population from the existential threat of too much inbreeding:

“A common breeding practice for pet dogs is mating between close relatives (e.g. between half- and full siblings). In a study of seven different French breeds of dogs (Bernese mountain dog, basset hound, Cairn terrier, Epagneul Breton, German Shepherd dog, Leonberger, and West Highland white terrier) it was found that inbreeding decreases litter size and survival.”

“Another analysis of data on 42,855 dachshund litters, found that as the inbreeding coefficient increased, litter size decreased and the percentage of stillborn puppies increased, thus indicating inbreeding depression. About 22% of boxer puppies die before reaching 7 weeks of age. Stillbirth is the most frequent cause of death, followed by infection. Mortality due to infection was found to increase significantly with increases in inbreeding.”

“Inbreeding Depression is considered to be due largely to the expression of homozygous deleterious recessive mutations. Outcrossing between unrelated individuals, including dogs of different breeds, results in the beneficial masking of deleterious recessive mutations in progeny.”
[End of Quoted Text]

It may well be that dogs are not unusual to produce these kinds of findings. I don’t know at this point. I don’t recall finding data on Inbreeding Depression in articles on other animals that humans are interested in.

Some more background information on the dog comes from the Wiki link below:

"The domestic dog (Canis lupus familiaris or Canis familiaris)[4] is a wolf-like canid in the genus Canis, and is the most widely abundant terrestrial carnivore. The dog and the extant gray wolf are sister taxa as modern wolves are not closely related to the wolves that were first domesticated, which implies that the direct ancestor of the dog is extinct."

“The origin of the domestic dog is not clear. It is known that the dog was the first domesticated species. The domestic dog is a member of the genus Canis (canines), which forms part of the wolf-like canids, and is the most widely abundant terrestrial carnivore.”

" The closest living relative of the dog is the gray wolf and there is no evidence of any other canine contributing to its genetic lineage. The dog and the extant gray wolf form two sister clades, with modern wolves not closely related to the wolves that were first domesticated. "

" The archaeological record shows the first undisputed dog remains buried beside humans 14,700 years ago, with disputed remains occurring 36,000 years ago. These dates imply that the earliest dogs arose in the time of human hunter-gatherers and not agriculturists."

“Where the genetic divergence of dog and wolf took place remains controversial, with the most plausible proposals spanning Western Europe, Central Asia, and East Asia.”

" This has been made more complicated by the most recent proposal that fits the available evidence, which is that an initial wolf population split into East and West Eurasian wolves, these were then domesticated independently before going extinct into two distinct dog populations between 14,000-6,400 years ago, and then the Western Eurasian dog population was partially and gradually replaced by East Asian dogs that were brought by humans at least 6,400 years ago."

27

Hey @beaglelady, thanks for the heads up with the article!

It gets right to the reasons why horses and donkeys do not create fertile offspring: “…can’t have babies of their own. They are sterile because they can’t make sperm or eggs. They have trouble making sperm or eggs because their chromosomes don’t match up well. And, to a lesser extent, because of their chromosome number. A mule gets 32 horse chromosomes from mom and 31 donkey chromosomes from dad for a total of 63 chromosomes. (A horse has 64 chromosomes and a donkey has 62).”

That’s certainly dramatic enough to catch a scientist’s attention!

In the formation of Ring Species, we must assume that the incompatibility between the two terminal ends of the population not usually because of mismatched counts of chromosomes. There is something less dramatic going on in these events of speciation…

Maybe I can find an article as specific as the one you found!

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J[quote=“gbrooks9, post:26, topic:37489”]
My point was more that I had no “skin” in the topic of wolves. I’m sure wolves, like predator species everywhere, make for a solid example of “speciation”. But bringing up wolves, when I’m discussing the unique characteristics of a non-wild (i.e., domesticated) animal population heavily manipulated by humans, doesn’t seem to send us in any particular direction.
[/quote]

Um, since dogs haven’t even properly speciated from wolves yet, you do have to make the comparison. Wolves are your control group, your null hypothesis. Whatever you think should or shouldn’t be happening with dog populations, comparing it with wolves is the only tool you have for seeing if it’s a real effect or not.

Let me interpret that Wikipedia article another way: dogs are more likely to be inbred by humans than crossbred. Human inbreeding of dogs is so bad that there’s a special term for the deleterious effects on dog health: Inbreeding Depression. If only humans would stop inbreeding dogs so much, we would have much healthier dogs.

This is bad news for a hypothesis which relies on humans wanting to crossbreed dogs more than they would ordinarily crossbreed in the wild, which, as I said earlier, is significant. I don’t see how humans breeding for ‘crossbreedability’ can continue to be a serious proposition.

But I’m sure that won’t stop you.

I guess I have never encountered those who think the domestic dog should be a hotbed of speciation, and if I did, I would simply say that there has not been enough accumulated genetic variation yet: increasing or dramatically altering the selection on a population doesn’t make variation grow any faster, although making dogs the most numerous carnivore on the planet might.

Merry Christmas!

29

How so? Dogs are one species, and there are several different species of wolves. What is properly speciated?

30

Last I checked, dogs were still Canis lupus familiarus, technically a subspecies of wolf, although this was still subject to some debate. Hence “properly speciated” would be without scientific doubt about classification.

I can check again, of course, if I’m out of date.

31

@Lynn_Munter,

Okay, let’s go with the foundation that you are laying down. Let’s see where it takes us:

  1. In your view, would you hazard a guess that the sensitivity to inbreeding is more-or-less uniform throughout the dog population?

  2. Or, would you predict that the sensitivity to inbreeding is uniform only amongst recognizable breeds - - while just plain mutts that are inbred suffer significantly less than the dogs in established breeds?

While it would be better for my model for point (1) to be true (whether dealing with mutts or breeds), intuitively it seems likely that point (2) would be more true than (1), wouldn’t you agree @Lynn_Munter?

Then there is the issue of wolves as a “control”. It’s interesting that you would say that. While your fixed determination to talk about the wolves traveling great distances doesn’t seem to be contribute to the discussion much, I will agree that Wolves are relevant (now) to the discussion in one important way:

If we inbred Wolves, which of three possible outcomes would you predict?

A) That they would suffer with the same high sensitivity as those dogs who are in formal breeds who have been inbred?

B) That they would suffer with the same moderate sensitivity as we presume non-breed domesticated dogs would?

C) That they would suffer with even less sensitivity than even non-breed domesticated dogs would?

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32

Since we know that Wolves and Dogs can produce fertile offspring, we are in the same territory that we find ourselves with the feline species:

Tigers and Lions may have very different appearances and temperaments, they are described as different species more out of consistency with tradition or convention than because they are reproductively incompatible. When mated, their mixed offspring are fertile (See the Wiki article on Ligers below.)

Tigers and Lions make a good example of how difficult it can be to trigger a truly distinct speciation: their common ancestors are estimated to have more recently than when Genus Panthera split from the rest of the Cats (“6 to 10 million years ago”), and so perhaps more recently than 6 million years ago:

Genus Panthera
Tiger (P. tigris)
Lion (P. leo)
Jaguar (P. onca)
Leopard (P. pardus)
Snow leopard (P. uncia)
Longdan tiger (P. zdanskyi)

Evolution
“The divergence of Pantherinae from Felinae has been estimated to have occurred between six and ten million years ago. DNA analysis suggests that the snow leopard Uncia uncia is basal to the entire Pantherinae and should be renamed Panthera uncia.”

Lions, living in the more open lands of Africa became more social and adapted to predatory strategies that involved teamwork.

While Tigers, adapting more to Asian jungle developed a different look and lived a more solitary lifestyle.

What could be more different than a Tiger and a Lion? And yet, genetically, they are still quite closely related - - enough to have fertile offspring.

33

You might be right. Will check.

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34

That seems true till you start to look at the literature. It’s really just not accurate. Here are just a few abstracts to think about.
Mechanisms by Which Phenotypic Plasticity Affects Adaptive Divergence and Ecological Speciation
Phenotypic divergence during speciation is inversely associated with differences in seasonal migration
Molecular investigation of genetic assimilation during the rapid adaptive radiations of East African cichlid fishes

The reality of phenotypic plasticity alone should motivate caution in assuming that divergence requires absolute genetic “speciation.”

3 Likes
35

Right, right.

As you know, I frequently discuss the fertile offspring of Lions mating with Tigers…

But I guess the “context” I was framing in my mind when I wrote that post is the YEC who complains that dramatic changes in phenotype are impossible. And while a Tiger and Lion mating might be considered a pretty surprising event, a YEC is all too likely to say that this is just variation within a single kind: the kind being “big cats”.

The flip side of the coin for me was tetrapod to whale… or rodent to bat… I would hazard the “wager” that all the big shifts involve speciation somewhere in the transition - - … anywhere from the beginning to the middle…

But you have some great links there, @sfmatheson.

I loved this discussion:

Am Nat. 2015 Nov;186(5):E126-43. doi: 10.1086/683231. Epub 2015 Oct 6.
Mechanisms by Which Phenotypic Plasticity Affects Adaptive Divergence and Ecological Speciation.
Nonaka E1, Svanbäck R, Thibert-Plante X, Englund G, Brännström Å.

Abstract
Phenotypic plasticity is the ability of one genotype to produce different phenotypes depending on environmental conditions. Several conceptual models emphasize the role of plasticity in promoting reproductive isolation and, ultimately, speciation in populations that forage on two or more resources.

These models predict that plasticity plays a critical role in the early stages of speciation, prior to genetic divergence, by facilitating fast phenotypic divergence. The ability to plastically express alternative phenotypes may, however, interfere with the early phase of the formation of reproductive barriers, especially in the absence of geographic barriers.

Here, we quantitatively investigate mechanisms under which plasticity can influence progress toward adaptive genetic diversification and ecological speciation. We use a stochastic, individual-based model of a predator-prey system incorporating sexual reproduction and mate choice in the predator. Our results show that evolving plasticity promotes the evolution of reproductive isolation under diversifying environments when individuals are able to correctly select a more profitable habitat with respect to their phenotypes (i.e., adaptive habitat choice) and to assortatively mate with relatively similar phenotypes.

On the other hand, plasticity facilitates the evolution of plastic generalists when individuals have a limited capacity for adaptive habitat choice. We conclude that plasticity can accelerate the evolution of a reproductive barrier toward adaptive diversification and ecological speciation through enhanced phenotypic differentiation between diverging phenotypes.

PMID: 26655782 DOI: 10.1086/683231

Sometimes attempts to “generalize” Evolution is foiled by the sheer breadth and scope of how Evolution can occur!

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36

I would say the results of inbreeding are worse the more previous inbreeding has happened, yes, and that it is particularly bad in established breeds. Some breeds are worse than others.

(Sorry, @gbrooks9 —hit ‘Post’ prematurely!)

It might depend which population of wolves you’re talking about. Some have been hunted down to very small population sizes, which would naturally result in inbreeding. However, I would expect them not to suffer as greatly as purebred dogs, who are often very unfit to surviving in the wild. I am less certain of choosing between B and C than I am that A is wrong, but if pushed to guess I would guess B. (ETA: changed my guess!)

There are right now wolves on Isle Royale in Minnesota dying out due to severe inbreeding from living on an island without being able to mix with other wolves. You could look into that if you’re interested.

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37

The definition of a species is that they usually can’t or don’t interbreed in the wild, which leaves a great deal open. Occasional crossbreeding does not make species definitions invalid. This is also why the definition of ring species is so problematic.

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@Lynn_Munter,

I think Myers was more specific: true speciation may not always be genetically triggered, but it would always be genetically confirmed. So a new bird variety that was triggered by a novel bird song showing up in a given generation could be the start of a new population. And we can understand how that would happen.

But he might not consider a new species to have emerged until, literally, no fertile offspring could be coaxed out of a cross-breeding effort, either in the wild or in the laboratory.

In my readings on Ring Species, I found that a lot of wasted energy was spent on whether or not a geographic obstacle was involved at some stage of the formation of the ring. They were not even discussing, say, a mountain range around which the Ring Species population would wrap itself… the “geographic obstacle” that would stymie the conversation was any additional obstacle (like a river or a spur of mountain range) that interrupted a free exchange of mating between two sub-groups.

In other words, some biologists insist that a true Ring Species is one where the only factor involved in genetic differentiation between sub-groups is the factor of distance - - even as the population wraps itself around the lip of a canyon, or a mountain range. The initial or central geographic feature is what makes it possible for the terminal ends of the entire population to encounter each other. And that’s fine. But if it is going to be a true Ring Species, there can be no other physical factor in reduced inter-breeding - - other than distances between groups.

But for our purposes, under the BioLogos umbrella, the beauty of Ring Species is not that there aren’t any physical barriers, but that we have all at the same time an early phase of a population and a late phase of the population, and we can measure genetic exchange rates that allowed these different phases to appear and or be sustained.

Sometimes YECs will read the negative comments of biologists about a population not being a true Ring Species, when all the biologist is complaining about is how the genetic differences emerged - - rather than whether there were any genetic differences.

For the sake of conversation, “reproduction in the field” has a certain pragmatic quality to it, but I think such a definition is too loose to help resolve issues when having complex discussions with YECs.

George

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39

I looked into this, and the latest research suggests that this is not the case. According to an article in the July 2015 article of Scientific American (Morell, Virginia, Scientific American, 00368733, Jul2015, Vol. 313, Issue 1):

Analyzing whole genomes of living dogs and wolves, last January’s study revealed that today’s Fidos are not the descendants of modern gray wolves. Instead the two species are sister taxa, descended from an unknown ancestor that has since gone extinct. “It was such a long-standing- view that the gray wolf we know today was around for hundreds of thousands of years and that dogs derived from them,” says Robert Wayne, an evolutionary geneticist at the University of California, Los Angeles. “We’re very surprised that they’re not.” Wayne led the first genetic studies proposing the ancestor-descendant relationship between the two species and more recently was one of the 30 co-authors of the latest study, published in PLOS Genetics, that debunked that notion.

I’d be happy to email you a copy of the article. Just PM me with your email address.

40

Or if you don’t want to give me your email address I can send you the article via a third party. I’ve already been sending Korvexius a bunch of articles.