>>Technically this is not geographic isolation, it is habitat partitioning. The animals are well within one another's geographic ranges (they are sympatric or parapatric in many areas) and dispersal areas. Besides, Gyrinophilus porphyriticus (the "surface species" ) is well known to use caves throughout its range.>>

They may be able to reach each other's habitat now, but it was apparently thought by some that in the past the cave salamanders were geographically isolated and thus evolved their cave adaptations like lost of eyesight and pigment. Once they have evolved these adaptations, the passage to the outside world reopened. But because "speciation" (which means different things to different people) has occurred, the 2 sibling species can no longer interbreed. That is the classic scenario of how isolation leads to speciation and it was probably what many people assume happened prior to the discovery of the amount of gene flow. But of course we now know that geographic isolation is not necessary.

>>You seem hung up on the idea that the ability to interbreed is proof of conspecificity. This is not a species definition supported by any working biologists that I am aware of, not even the late great Ernst Mayr who first laid out the biological species concept.>>

You misunderstand. I do not consider the ability to interbreed as proof of conspecificity. Otherwise, the corn snake could easily be classified as the same species as the common kingsnake, given their ability to produce hybrids in captivity. Instead, I consider the inability to interbreed as evidence that two populations are not the same species. Ernst Mayr points out that it is very easy to tell if two sympatric populations are conspecific, because if they do not interbreed freely, then they are two distinct species. It is much more difficult when two populations are allopatric. In that case the ability to interbreed may or may not be proof of conspecificity.

>>The fact that gene flow could occur if two populations (let's use your eastern and California tiger salamanders as an example) were sympatric does not reflect the fact that gene flow is not occurring. The two populations are as isolated from another as they are from pigeons or hedgehogs. Of course this reasoning can be taken too far (does each of the many isolated populations of four-toed salamanders deserve species status?), but I think you are in an indefensible position by claiming interbreeding=conspecificity.>>

Quite the contrary. According to Mayr, a species can consist of a group of potentially interbreeding populations. A. t. californiense and other subspecies of A. tigrinum clearly fit that description. They both retain the potential to interbreed. OTOH, those who treat geographically isolated populations as distinct species are really in an indefensible position.

>>Reproductive incompatibility, whether behavioral, physical, or genetic, is often evolved in closely related species that are sympatric to guard against hybridization; there is no reason for allopatrically distributed species to evolve such safeguards. This does not make them conspecific.>>

It is true that pre- and post- mating isolation mechanisms often evolve when two closely related species are sympatric with each other. Once again, we can point to the African cichlid fishes. These diverse species, which evolved in sympatry from a common ancestor, also evolved reproductive isolation mechanisms to guard against hybridization because hybrids are less fit. Hence one can infer species status indirectly by evaluating whether hybrids are less fit or not. In some cases, it is easy. For example, Hyla versicolor and H. chrysoscelis crosses are obviously unfit. In other cases it is not as easy. In the case of tiger salamander hybrids, it appears that they are every bit as fit as the native species because the researchers who worked with them fear that these hybrids may become dominant at the expense of the natives

>>It is my impression that the gray wolf/coyote hybrid origin for red wolves is speculative only; if you have links to any research on the issue I would be glad to read it.>>

Here is one link, with references therein.

http://www.montana.edu/~wwwbi/staff/creel/bio480/The red wolf.pdf

>>The Eumeces (I guess it's now Plestiodon) gilberti stuff is very interesting; it must be a fairly simple genetic cause to allow multiple independent origins from the E. skiltonianus stock. The same has been shown in the tetraploid gray tree frog Hyla versicolor.>>

I don't know what the underlying genetic mechanism is, but there is evidence that this ability to give rise to different ecological types exist in the Eumeces species found in Asia.

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