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RE: C. bottae taxonomy

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Posted by: CKing at Thu Dec 4 08:09:39 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  

>>Of interest is the notion you proposed that at some point in time, the Rubber Boa may have dispersed southward in part of its range. >>

Yes, the rubber boa probably dispersed southward to northern Baja California and probably occupied the mountains of San Diego County, Orange County, Coastal Los Angeles County (Santa Monica and San Gabriel Mountains) as well as Ventura County and Santa Barbara County in the past. The large morph Northwestern subclade no doubt migrated from southern Kern County to coastal San Luis Obispo and Monterey Counties via the Sierra Madre but currently there is a distributional gap between the Northwestern subclade and the Kern County boas.

The Rosy Boa originated in northern Baja California according to a recent mtDNA paper, and IMO, this population was once indistinguishable from the rubber boa. Climatic changes probably caused most populations of the rubber boa in Southern California to become extinct. Similarly, we see evidence of such extinction in L. zonata. There almost certainly were L. zonata in the mountains of San Diego Co., Los Angeles Co., San Bernardino County and Orange County at the time the rubber boa occupied this same area, but they all became extinct along with the rubber boa in these mountains.

Instead of seeing L. zonata lineages that rival those of L. z. agalma and L. z. multifasciata in lineage age, which is what is expected if there were no past extinction event, all of the Southern California populations assignable to L. z. parvirubra and L. z. pulchras are very recent lineages derived from L. z. agalma. In fact, the extinction of L. zonata in southern California was even more complete than Charina bottae.

C. bottae managed to hang on, but barely, in the San Bernardino or San Jacinto Mountains. All of the C. bottae populations of these two mountain areas have only recently diverged from a single common ancestor according to mtDNA, suggesting that C. bottae was reduced to a very small population in one of these mountains in the relatively recent past. If biologists think that the southern Rubber boa is endangered now, they might have thought that it was extinct if they can travel back in time when there was probably just a single small population hanging on for dear life.

>> Going one step further, perhaps at one time, all of the mountainous regions in Kern, Ventura, Los Angeles, San Bernardino, and Riverside Counties (and south into Mexico) of S. Calif. may have been too warm and dry for the existence of C. bottae. >>

That is probable. Not only C. bottae, but L. zonata, as well as the blotched form of Ensatina, show signs that they had at one time became extinct or have severely limited distributions in these areas.

>>Could it be possible that the only remaining refuge for the species was in the high elevations of the southern Sierras in Tulare and Inyo Counties (Mt. Whitney region) and it was from there that the species then expanded in all directions when suitable environmental conditions returned to the mountainous regions to the south.>>
>>That is, I now wonder if the species was once extinct in the San Bernardino and San Jacinto Mts. (and elsewhere in S. Calif.) and those areas were recolonized from the dwarf morph that occurs in the southern Kern Plateau in Tulare County. >>

It is certainly possible but not probable. The Tulare County boas are a relatively recent lineage (with the possible exception of the recently discovered umbratica haplotype). If C. bottae migrated from Tulare to San Bernardino County, then we should see small morph snakes with the umbratica haplotype in Southern Kern County. Instead, we see haplotypes that are more derived than #26 in these localities. The San Bernardino and San Jacinto Mountain populations are all descended from a common ancestor very recently, but this common ancestor is very different than sample #26 of Tulare County.

>>Perhaps the newest results indicate the reverse, that the dwarf Southern Clade boas in the Kern Plateau arose from the population in the San Bernardino Mts. It seems you have mentioned that age and lineage can be inferred from the raw mtDNA results or am I wrong in that respect?>>

I haven’t seen the new data. It will depend on how the Tulare Co. specimen with the umbratica haplotype is related to the other boas and to San Bernardino County boas. It is certainly possible that the San Bernardino Mt. Boas are derived from the Tulare County boa with the umbratica haplotype, but the haplotypes of the Kern County boas (samples #30-32) argue against this scenario.

>>Arguing against the north to south dispersal scenario is that the Mt. Pinos population seems to be closer morphologically (scale counts and configurations) to the San Bernardino boa population than the dwarf boas from Breckenridge Mt. to the north. On the other hand, just this past year, I did find a few boas from Mt. Pinos with maximum dorsal scale row counts in the 44 - 46 range which overlap the lower range of the large morph boas from the Sierras. That scenario does suggest an influence from more northern populations.
>>The sample of dwarf boas I have examined from the Kern Plateau is only about 8 - 10 specimens. So at this point, it is not possible to make a reliable comparison of scale counts and head scale configurations between that population and the populations that occur in the San Bernardino Mts.and elsewhere. At any rate, up to now, I had only been thinking of how the Southern Clade dwarf boas dispersed northward from the San Bernardino Mts. to the Kern Plateau and not the reverse.
>>Your point about having greater representation in areas were clades or subclades were likely to meet was the same argument I presented to Rick and Glenn. And that is why they agreed to test additional samples from the area near Mt. Lassen, from the southern and northern part of the Greenhorn Mts., and from the S. Kern Plateau in which the dwarf vs. large morph scenario was also at play.
>>And another intriguing aspect of the species is what mechanism(s) are at play that has kept the two morphs reasonably distinct in the Sierra Nevada Mts.? That is, why hasn't the large morph over-run the dwarf form in the southern Greenhorn Mts. and on the southern Kern Plateau? Or conversely, is the dwarf form expanding its distribution into large morph territory?
>>Richard F. Hoyer

According to the new mtDNA data you disclosed, it appeared that the Northwestern subclade has successfully invaded the northern Sierra Nevada Mountains, and it seems to be outcompeting the Sierra Mountain subclade because the Sierra Nevada Mountain subclade has not dispersed into Northwestern subclade territory. This pattern is the exact reversal of the L. zonata dispersal. In L. zonata, the Sierra Nevada subspecies (L. z. multicincta) has invaded territory used to be occupied by L. z. multifasciata, which shows one remnant population in the vicinity of Ashland, Jackson Co. Oregon. Evidence of L. z. multifasciata influence is the large intergrade zone between L. z. “zonata” and L. z. multicincta, based on morphological grounds. All of the Northern California specimens in the range of L. z. “zonata” have haplotypes belonging to the Sierra Mountain sublclade. That means L. z. “zonata” is actually either L. z. multicincta or L. z. multicincta x L. z. multifasciata.

The Northwestern subclade is probably geographically isolated from the Kern County boas. There appears to be a large gap between the southernmost Northwestern subclade specimen in San Luis Obispo County and the northernmost small morph Kern County speciments. That would probably account for the ability of the small morph to persist in this area. It is shielded from the Northwestern subclade, the most successful lineage within C. bottae. Although some of the Tulare County boas are “large morph,” this particular morph appears to have evolved independently of the Northwestern subclade, since it evolved after the Northwestern subclade last shared a common ancestor with sample #26 and all other Sierra Nevada subclade snakes. Perhaps the Sierra Nevada “large morph” is a more benign competitor and it is able to coexist with the small morph. The Northwestern subclade, for whatever reason, has managed to invade the Sierra Nevada Mountains while preventing the Sierra Nevada subclade from making excursions into its territory. To this date, there is no data to suggest that they can coexist at the same locality.

In the past, I have suggested that it is possible that the Northwestern subclade may have evolved into a different species. However, in view of the gap (now gone) in the distribution of the Sierra Nevada and Norhwestern subclades, there was no data to show whether they have evolved reproductive isolation. I now believe that this question may need to be re-examined in view of new data that shows the Northwestern subclade outcompeting the Sierra Nevada subclade at the intersection of their distribution. Is it possible that the Northwestern subclade individuals simply do not recognize the Sierra Nevada subclade as conspecific and vice versa, therefore there is no intergradation? Or is the sample too small to show evidence of intergradation? Or is it possible that the Northwestern subclade intergrades with the Sierra Nevada subclade but the hybrids are maladaptive? At the same time, the Northwestern subclade seems to be better competitors against the Sierra Nevada subclade. Could it be a combination of both factors which has allowed the Northwestern subclade to expand its range at the expense of the Sierra Nevada subclade.

Could it be body size that allowed the Northwestern subclade to dominate? The record length for L. zonata has been reported in a specimen from the Sierra Nevada Mountains. That means L. z. multicincta probably was able to evolve a larger body size than L. z. multifasciata. The larger body size may have allowed L. z. multicincta to outcompete L. z. multifasciata in Oregon and Northern California north of Sonoma County. Perhaps larger body size allowed the Northwestern subclade of the rubber boa to gain an upper hand on the Sierra Nevada subclade?


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