Are dogs a Ring Species?

[Daecon]

I can't imagine a Chihuahua ever producing offspring with a Great Dane... they'd never get past gestation for one thing!

 

Would this essentially make different breeds of dogs forever unable to interbreed with each other, and thus mean they are different species?

[Moontanman]

Um, why couldn't a Great Dane bitch have puppies by a chihuahua sire?

[D H]

Would this essentially make different breeds of dogs forever unable to interbreed with each other, and thus mean they are different species?

No. While a Chihuahua-Dane cross might be problematic, Chihuahua-Shepherd and Dane-Shepherd crosses are not (Google is your friend). Dogs revert to the standard street mutt in just a couple generations -- if they survive. Survival for small breeds, if let run loose, is suspect. Dogs are neotenized wolves, small dogs much more so than big dogs. Like corn, which cannot survive in the wild, our domestication of the dog has bred a lot of the very traits needed for survival out of them. Toy breeds act like puppies (very young puppies) for their entire life because they essentially are puppies for their entire life.

[Daecon]

No. While a Chihuahua-Dane cross might be problematic,

Which is what I'm referring to. Would a Chihuahua and a Great Dane be considered separate species with regard to each other?

 

I'm aware that different sizes can interbreed with each other, but the two extremes?

 

If A & B can, B & C can, C & D can but A & D can't, even though they can be linked together through other breeds, are they still the same species compared to each other?

[D H]

Yes.

[Daecon]

Ah, okay. I just asked because I was reading an article on Wikipedia about Salamanders and wondered if it applied to dogs, too.

The Ensatina salamander has been described as a ring species in the mountains surrounding the Californian Central Valley. The complex forms a horseshoe shape around the mountains, and though interbreeding can happen between each of the 19 populations around the horseshoe, the Ensatina eschscholtzii subspecies on the western end of the horseshoe cannot interbreed with the Ensatina klauberi on the eastern end. As such it is thought to be an example of incipient speciation, and provides an illustration of "nearly all stages in a speciation process"

[D H]

There's a big difference between natural selection and artificial selection. Nature tends to select favorable mutations. We tend to select recessive mutations that in nature would be extremely disadvantageous: Wolves that don't mature properly (dogs), bovines with ridiculously large udders (milk cows), grasses that don't scatter their seeds properly (almost all grains, corn or maize being the worst).

[Mokele]

I think the main issue is that "ring species" hinges on geography. What you describe for dogs would be more like simple divergence, admittedly incomplete divergence.

 

The biological species concept (that the definition of species is being unable to breed) is not without its flaws, and how it applies to domesticated species is tricky, to say the least. Generally, most biologists don't consider "breeds" of any domesticated organism (plant or animal) to be species.