Ensign Morituri

This issue has been bugging me for the longest time.

Is it possible (through artificial insemination, I would hope) for a Chihuahua and Great Dane to have viable offspring?

If not (and I'm only assuming that this is the case), could speciation be said to have occurred between these two breeds?

Coragyps

My vote is that they have speciated - just like the greenish warblers around the Himilayas. The birds are a "ring species" by behavior - the adjoining "ends" of the ring don't recognize each other's song. The dogs are reproductively isolated by size. Humans just happened to be involved in the diversification of the ur-dog(s).

Late_Cretaceous

If you wiped out all breeds of dog except for the Chihuahua and Great Dane, they would most certainly be considered different species.

There are many species of spuce that are considered different only because they shed thier pollen at different times, therefore resulting in reproductive isolation ( in spite of the fact that they can interbreed).

Minnesota

The fertility/infertility criterion, once popularly used as a bench mark for determining species/non-species, has pretty much been thrown out. For one thing, there are too many exceptions to make it binding----wolf-coyote-dog interfertility being one example. In fact, just recently, the American Association of Mammalogists decided to reclassify the domestic dog, Canis familiaris as Canis lupus familiaris, a subspecies of wolf. So, the Chihuahua and Great Dane have not only NOT "speciated," but they haven't even "subspeciated." The Chihuahua and Great Dane are, indeed, capable of producing viable offspring. And, I have not read a thing to indicate that the two are reproductively isolated because of size. Also keep in mind that dogs are breeds: artificially created variants, and therefore not recognized as potential individual species. Species are almost without exception considered to be naturally occurring variants of a form.

demoninho

Ensign Morituri, I was wondering are you also active on www.terdiscussie.nl? Because I was debating the sometimes arbitrairy distinction between species, using the same example.

Wounded King

Or perhaps you've looked at the EvC forum where there has just been a discussion of the same issue on this thread.

Wounded King

Minnesota, in what way has the Biological Species Concept, that a species is a set of actually or potentially interbreeding organisms, been 'thrown out'? The 'exceptions' simply show that the groupings of species developed previously had completely different criteria to the BSC. Or ar you meaning that the question of interfertility in an experimental setting is no longer considered?

you say

This sounds suspiciously like trying to sneak Kinds in by pretending that is the generally accepted idea.

demoninho

Well, I guess it's the internet all people with the same questions

Minnesota

Hardly

The biological sciences have yet to come up with a universal definition of "species." The various species concepts now in use have arisen out of the need to address classification issues often particular to only one branch or sphere of biology, and therefore are seldom widely applicable. These concepts include biological, biosystematic, evolutionary, genetic, moropological, paleontological, and phylogenetic definitions.

The most widely used of these definitions, based on the biological concept of species, usually takes a form akin to that formulated by biologist Ernst Mayr. Mayr contends that a species is a "reproductively isolated aggregate of populations which can interbreed with one another because they share the same isolating mechanisms." The heart of this definition lies in the criterion of reproductive isolation.

Reproductive isolation embraces any element of nature that prevents the reproduction of fully viable offspring. Some of these elements keep organisms apart before they can mate. These include ecological barriers, which physically keep populations from meeting; temporal barriers, wherein species breed at different times of the day or year; behavioral barriers, where organisms consciously reject, for whatever reason, other organisms; and mechanical barriers, such as incompatible physical or physiological differences in the two organisms. Other prohibitive elements occur after mating has taken place. These include cases where the sperm and egg do not reach each other or fail to fuse; where a hybrid dies before it sexually matures; and where the hybrid is sterile. Note, the essence of this definition of species is the ability of two organisms to successfully reproduce by mating. But, of course ,we know that there are many species that do not mate in order to reproduce, self-pollenating flowers being a prime example.

Wounded King

Thats a fairly good summary but doesn't actually answer my question. When you said were you meaning that a strict interpretation based on genetic/ sperm-egg interaction reproductive isolation had been 'thrown out' in favour of a more general concept of reproductive isolation as seen in the BSC?

As to the last sentence in your first post, I see now that I took it out of its context with the previous sentence about artificial selection.