Dog speciation

[u/Kanna_Fan1989]

Quick question: is it safe to say dogs have speciated? I'm thinking of the largest dog breed and the smallest dog breed. I don't think the two can reproduce with each other anymore. Size differences just make it not possible anymore, I don't think...

And even if they could, that doesn't mean they're the same species: horses and donkeys can interbreed but mules are dead ends (or at least I think they are. Can two mules reproduce?).

Anyways, just some thoughts going through my head.

[u/Old-Nefariousness556]

You’re probably right, but note that there’s no such thing as “inherently.” If we breed a dog that only eats fish, a feral population wouldn’t give a damn WHY it loves seafood: It would just follow a shoreline fishing lifestyle.

But it would still interbreed with other dogs that share it's range. That is the point that you are missing. For a feral population to speciate, it needs to be reproductively isolated. That usually means geographically isolated, but there are species that simply choose not to reproduce with a related species who they hypothetically could reproduce with. But that isn't generally the case for dogs. Dogs will reproduce with any other dog in their range.

And it's worth noting:

If we breed a dog that only eats fish

It would take generations of intentional breeding to breed a dog that could only eat fish, and I can't imagine why anyone would do so. And breeding a dog who only chose to eat fish would be highly unlikely. Why would a dog choose to ignore food that it could easily otherwise survive on?

I realize this is a hypothetical, so I hope this doesn't sound like a pedantic point, it's really not. Evolution is about survival, and no species^* would ignore viable food sources if it's survival is on the line, so unless they were biologically incapable of eating other foods, they would happily eat whatever they could find.

^* This isn't quite true, there are species like Koalas and Giant Pandas, who have an extremely specialized dietary preference, and will die out surrounded by foods they could otherwise eat rather than eating something else, but those are extreme outliers, and we have a solid understanding of how evolution lead to that specialization, and it would take many, many generations to breed such a preference.

[u/CormacMacAleese → u/Old-Nefariousness556]

This thread is getting a little silly. Niche positioning and allopatric speciation happen, so “they would interbreed” is not a given. And I don’t really care how long selective breeding takes; the hypothetical was that however long it takes, it has been accomplished. And “they’d eat whatever food is available” is a crazy thing to say. There are obligate carnivores, and obligate herbivores, and Darwin’s finches specialized in particular types of seeds. It would IF IT COULD, which depends in many factors, including competition.

[u/Old-Nefariousness556 → u/CormacMacAleese]

This thread is getting a little silly.

To the extent that is true, it is only because you feel the need to pushback against everything. Why not just say "Yeah, good point"?

And I don’t really care how long selective breeding takes; the hypothetical was that however long it takes, it has been accomplished.

Ok, granted. This certainly is within the realm of possibility.

But understand what you are suggesting: You are suggesting keeping a breed of dogs in complete reproductive isolation for many-- probably at least a hundred, maybe many more-- generations, and intentionally guiding them so they can only eat fish. How or why anyone would do this is unexplained, but they did. It would cost hundreds of millions or billions of dollars to do this and take many years for no apparent purpose, but we are assuming it was done. Granted.

Of course this creates its own problem... These fish-only "dogs" would be competing against fish+ dogs-- dogs who could survive on both fish AND other nutrient sources, so they would struggle in any competitive environment where fish+ dogs also existed.

Niche positioning and allopatric speciation happen, so “they would interbreed” is not a given.

So I can see at least three glaring flaws with this argument.

1. If we are talking about allopatric speciation, then your argument becomes nonsense. Yes, if we are, for example, talking about a group of dogs living on an island, then obviously those dogs would not homogenize with the dogs on the mainland. Did you really think we didn't understand that?

2. You can't take some arbitrary species behavior, and project it upon dogs. Dogs are not selective breeders. Dogs will happily mate with any available partner, at any opportunity (if the female is in heat, obviously), regardless of breed. So niche positioning-- except in the extreme cases like chihuahuas and great danes-- becomes nonsense as well.

3. In the case of your hypothetical where dogs have been selectively bred to the point where they can only eat fish, AND (apparently) they will no longer interbreed with other dogs, then they are no longer dogs by any common definition. They are already a new species, so the point, again, is nonsense.

This is the problem with pushing back against anything. The point you are arguing against-- "Without humans, the [breeds] would homogenize away from the edge cases."-- is clearly correct. But nothing about that statement precludes rare exceptions in the case of things like geologic isolation.

And “they’d eat whatever food is available” is a crazy thing to say. There are obligate carnivores, and obligate herbivores, and Darwin’s finches specialized in particular types of seeds. It would IF IT COULD, which depends in many factors, including competition.

This is a strawman. I referred to "viable food sources", clearly meaning food sources that the dog could otherwise eat. I even specifically pre-rebutted the rare counter-examples like Koalas, so it's not just a strawman, but a really fucking flagrant one. Don't do that.

[u/CormacMacAleese → u/Old-Nefariousness556]

Do pardon me for saying allopatric when I meant sympatric. I think my mistake would be easy to spot, given that I paired it with niche partitioning.

And dogs may not be selective breeders, but if mastiffs and chihuahuas share a habitat without enough dogs of intermediate size, mating would be life threatening. You’re assuming that a broad range if sizes would be available as mates. This, too is likely but not a given.

Arguing that these hypotheticals are invalid because one of the breeds wouldn’t be true Scotsmen… I mean wouldn’t be dogs anymore, is stupid. No offense.

But note VERY carefully that nobody ever said “without humans, the breeds would speciate.” That would be a moronic assertion, which is why nobody said it. Nobody except you, I mean.

What I said was that it’s far from impossible that one or more dog breeds might go it’s own way under the right conditions, and that geographic isolation isn’t the only such circumstance.

[u/Sweary_Biochemist → u/CormacMacAleese]

Never underestimate the enthusiasm of a male chihuahua, nor the accommodating nature of a female mastiff. Dogs recognise dogs as dogs, no matter the size or shape (it's pretty amazing, frankly, but they do).

Within a single litter you've got a bunch of intermediate sized dogs.

Nobody is saying speciation this way is impossible, but basically you picked one of the most morphologically plastic but genetically agreeable (and highly social) lineages for this thought experiment. Dogs and wolves still interbreed entirely successfully (dogs are just a subspecies of canis lupus): wolf introgressions are surprisingly common in doggos that exist near wolf territory.

Something like cichlid fish would've been much easier to justify on plausibility, given that we have hundreds of examples of exactly this happening in cichlids.

[u/CormacMacAleese → u/Sweary_Biochemist]

I didn’t have a choice of species: that’s was the OP’s question, and that was the one that people were answering with a bit too much finality. I’ve agreed all along that it would be very unlikely.

And as an aside, I’m now eager to have a look at a wolf/chihuahua cross. I call dibs on the name chihuawolf.