at Tue Nov 25 22:40:10 2008 [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]
>>Because the officially recognized SRB subspecies occurs as isolated populations only in the San Bernardino and San Jacinto Mts., it probably has been considerable time since any gene flow occurred between those populations and C. b. bottae.>>
Yes, that is what the mtDNA data shows.
>>However, if one includes the Southern Clade boa population that occurs in the southern Kern Plateau, then gene flow between the Southern and Northern Clades has likely been ongoing for eons somewhere in Tulare and Inyo counties . >>
Not quite. The mtDNA tree shows an unresolved polytomy between most populations of the Sierra Nevada subclade and shallow mtDNA divergences among the mtDNA haplotypes of the Sierra Nevada Mountain populations. Together these two aspects of the mtDNA data suggests that the small morph rubber boas of the Kern County area, after becoming isolated from the southern California populations, gave rise to the Northwestern subclade, but subsequently the population contracted. The once continuous distribution of the Northwestern and Kern County boas was severed. In fact, the mtDNA haplotype of the Kern County boas suggest that they are derived from the Tulare County (#26) boa at about the same time that this same population gave rise to the Sierra Nevada Mountain populations, and more recently than the Northwestern subclade/Kern Plateau boa split. Hence the current Tular/Kern County animals have been isolated from both the Northwestern and Southern California boas for long periods of time without any gene flow among these three populations. That is why we don't see large morph phenotype animlas in the Tulare County and Kern County populations, at least this is the testable prediction of my theory of the evolutionary history of this species.
>>Before I undertook the SRB study during 1993 - 1997, I had doubts about the SRB being recognized as a distinct subspecies. But during that study, the population in the San Bernardino Mts. did seem pretty unique at the time. The characteristic described for the subspecies by Klauber in 1943 from only two specimens, are rather consistent in the SRBs in the San Bernardino Mts. No one has undertaken a study of the SRB in the San Jacinto Mts. so nothing of much certainty can be said about that population.
>>Since that time, I have discovered that 1) there are other boa populations that similar to the SRBs, are also of the dwarf morph and 2) considerable overlap in defining traits occur between the SRB and other Northern Clade boa populations in S. Calif. So the subspecies designation comes into question again.
As I suggested in my earlier posts, the SRB should be grouped in the same subspecies as the dwarf morph boas of Kern and Tulare County. These populations almost certainly represent the ancestral morphotype from which other populations have evolved.
>>The mtDNA data however, is a powerful argument in favor of subspecies status. I know little about taxonomy per se and thus leave it up to those more versed to sort out the pros and cons. >>
The subspecies category is an informal one, and there is no requirement that anyone recognize it. However, many biologists, as Ernst Mayr and others have pointed out, find the subspecies category useful and they therefore use it for pragmatic reasons. However, some taxonomists do object to the use of the subspecies category for ideological reasons, so they tend to either elevate subspecies to full species status (often without good reason) or else find an excuse not to recognize any subspecies at all. Unfortunately, Rodriguez-Robles et al. seem to fit the ideological category. That is why they found a reason (which you believe to be invalid) to elevate umbratica to full species. That is also why Rodriguez-Robles argued that no subspecies should be recognized in Lampropeltis zonata.
>>I have never considered umbratica as a separate species.>>
Good for you. And I agree with you. The supposed morphological differences between umbratica and the other populatioins have been falsified by your data. And even if they are valid, these differences can best be used to delineate subspecies, not species. Species ought to be delineated on the basis of reproductive isolation, not minor morphological differences.
>>Well before Javier's publication, I was aware that to much overlap in defining traits occurred between the SRB and boas from other populations including one population in SW Oregon. Then with my examination of other boa populations in S. Calif., and in particular the Mt. Pinos boa population, with the amount of overlap of key traits, those boas make a mockery of the subspecies designations----but only from a morphological perspective.
>>With the discovery of the Southern Clade occurring in the Kern Plateau, not only does that revelation likely sink the separate species scenario, it probably puts into question the subspecies designation as well.>>
That would be true if we define umbratica as only those animals from San Bernardino and San Jacinto Mountains. A better definition of umbratica, in my view, is to include the dwarf morph Kern County and Tular County boas in umbratica. Since the Northwestern and Sierra Nevada Mountain rubber boas are both large morph, umbratica becomes a tenable designation for the dwarf morph populations. C. b. umbratica would be paraphyletic, but that is not inconsistent with any aspect of traditional taxonomy, although it may upset some cladists.
>>Perhaps it may come down to just how much divergence occurs between the San Bernardino and San Jacinto Mts. populations and the Southern Clade boas that occur on the Kern Plateau.
>>Richard F. Hoyer
The "divergence" between these populations, in terms of mtDNA, is large, larger than that between the Kern Plateau populations and either the Sierra Nevada Mountain or Northwestern subclades. Morphologically, the divergence appears small, as they are both small morph snakes. If other characteristics that are traditionally used in snake taxonomy do not show a marked dichotomy, then these two populations should definitely be combined into the subspecies umbratica.
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