>>CK,
>>Actually, I have some fragmentary evidence of where the dwarf and large morphs may intergrade in the Greenhorn Mts. of southern Tulare county.>>

If I remember correctly, the Greenhorn Mts. is approximately the northern limit of L. z. multifasciata. North of this area L. z. multicincta predominates. That is why I said there seems to be an invisible line in Tulare County, north of which lies the large morph rubber boas and L. z. multicincta and south of which can be found small morph rubber boas and L. z. multifasciata.

>>I recorded data from about 17 specimens in that region. The data suggest a mixture of the two morphs and thus I have tentatively considered that region to be where the two morphs intergrade.>>

It is possible that this is the zone of intergradation. However, small and large morph Sierra Nevada subclade snakes have similar mtDNA haplotypes.

>>The crosses I have initiated have been designed to try and determine just what genetic mechanism might account for the two morphs being able to retain their separate identities in face of the prospect they must come in contact and hybridize. >>

Some of the data you gave suggest that size is somehow sex linked. So if they intergrade, the different size morphs can remain distinct since there is no blending inheritance.

>>I have tentatively assigned the boa population in the southern Greenhorn Mts. south of Alta Sierra and hwy. 155 as being the dwarf morph as the few specimens from that region suggest they are dwarf. Voucher specimens from the vicinity of Sequoia Nat. Park indicate the large morph occurs in that part of Tulare Co. And thus those 17 specimens found in-between are of particular interest. And here is where future nuclear DNA research would be indicated. If one or more markers could be found that identify the dwarf from the large morph, then testing those 17 specimens could potentially provide some insight.>>

That would take an awful lot of work of mapping the entire genome and then finding the particular gene responsible. I am not sure there would be funding to do that and I am not sure if anyone would spend that much time and effort to identify the genetic basis for that one trait.

>>As mentioned, totally unknown is just how far the dwarf from occurs on the Kern Plateau before it most assuredly comes in contact with the large morph. And as mentioned,
>>another unknown is if the dwarf form occurs all the way to the extreme southwest region of the Kern Plateau just east of Kernville. If I were younger, that would be one of the areas in which I would conduct searches for the species.
>>
>>Richad F. Hoyer

It appears from what you have told me so far, that all the boas found within Kern County should be the dwarf form. This is the most likely scenario: the dwarf form is ancestral, and one large morph evolved from the small morph ancestor, as the Northwestern subclade, and migrated north along the coast into northern and central California, Oregon, Idaho and Utah. The dwarf morph in the south remained largely unchanged morphologically until one population reached the area north of the Greenhorn Mountains, where it evolved into the large morph and then migrated north to the area just south of the Mt. Lassen area, but could go no further. Perhaps the small morph also took a separate route and migrated northeast, around the eastern slopes of the Sierra Nevada and into western Nevada. Or perhaps the Northwestern subclade went around the Sierra Nevada and into the state of Nevada before expanding its range south and back into southeastern California. mtDNA data would probably provide an answer to these questions because mtDNA is an excellent set of markers for tracing ancestor-descendant relationships.

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