Hi Richard, thank you very much for your thoughtful response. After reading the new information you have provided concerning additional specimens and localities, I must nevertheless conclude that these new specimens have not disproven Rodriguez-Robles' claim that the two large morph subclades are completely allopatric. He apparently based his claim on his mtDNA data, which shows that at any one locality, only one or the other large morph mtDNA haplotypes are present, but not both. Now, if someone, anyone, were to come up with new data which shows that both of the large morph mtDNA haplotypes are in fact present at a single locality, then the claim of complete allopatry can be falsified.

The mtDNA data suggests that the Northwestern large morph lineage migrated along the coast westward from western Kern County, and then expanded its range northward and thence eastward to occupy much of the present range of the rubber boa north of Kern County, but exclusive of the Sierra Nevada Mountain Range. And this migration apparently took place before the Sierra Nevada large morph even evolved, because the small morph Kern County boas show a closer genetic relationship to the Sierra Nevada large morph snakes than either of them does to the Northwestern large morph. In other words, the Sierra Nevada large morph and Kern County small morph boas share a more recent common ancestor with each other than either of them does with the Northwestern large morph boas. That determination comes straight from the mtDNA data of Rodriguez-Robles et al. To me that suggests the common ancestor of the Northwestern (large morph) and Kern County boas was very likely a dwarf morph snake. The 2 subsequent lineages that came from this common ancestor went their separate ways, one along the coast and became exclusively large morph, and the other along the Sierra Nevada Mountains, but remaining small morph until a large morph population evolved later in the Sierra Nevada Mountains north of Kern County. And these two large morphs apparently have never met.

As I said earlier, there is no mtDNA data to demonstrate that the Northwestern large morph has ever met the Sierra Nevada large morph. I understand your objection to this claim because you believe that the area between the supposed gap in distribution is suitable habitat for boas and some boas have been found within this gap. Unfortunately, there is no mtDNA data from these specimens to show which population they originated from, and more importantly, there is no data to show that both types occur in the same locality. Until that data becomes available, Rodriguez-Robles claim of complete allopatry remains the best supported theory. Like all scientific theories, however, it can be falsified by additional data.

It is unfortunate that no crosses have been attempted between Northwestern large morph and Sierra Nevada large morph boas. Of course there is every reason to believe that they are probably reproductively compatible, because they are morphologically similar, which suggests that neither has evolved into a different species. But then again, reproductive compatibility cannot be assumed. It must be demonstrated. Of course it is equally untenable to assume that they cannot interbreed. Hence I do not support splitting the Northwestern and Sierra Nevada large morph snakes into different species because of allopatry. The best solution would be to treat them as different subspecies, as least for the time being. Lumping them on the basis of their similarity as large morph snakes is unacceptable because they apparently evolved their large morph phenotypes independently of each other. As I said in another post, lumping the 2 large morphs would be similar to lumping Lampropeltis getulus niger and L. g. nigritus as a single species because they both show a propensity for melanism.

Finally, your crosses between small morph and large morph snakes seem very interesting, as size seems to be linked with sex somehow. Are these crosses between Northwestern large morph and small morph snakes or are these crosses between Sierra Nevada large morph and the small morph snakes?

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