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RE: C. bottae taxonomy

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Posted by: RichardFHoyer at Fri May 16 17:45:12 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by RichardFHoyer ]  
   

CK,
Conjecture and other forms of speculation are commonly included in the 'Discussion' sections of published accounts. However, in this particular instance where different forms of a species potentially meet in a zone of intergradation, it would be important that large sample size and geographical representation is needed in order to make assertions that would engender a reasonable degree of confidence. From my perspective, not finding overlap of mtDNA on the basis of two random samples at a stated distance of 120 km apart is not the type of evidence upon which to arrive at a conclusion of allopatry and produce any degree of confidence.

Without having adequate geographical representation, assumptions should instead be based on existing evidence coupled with applying basic biological principles. Thus, with continuous suitable Rubber Boa habitat occurring in all directions in the greater Mt. Lassen region, with no evidence of existing barriers, with no known potential barriers in recent history perhaps as far back as the last ice age, and no documented break in distribution of the species in that region, early on I considered it to be a given that members of both subclades overlap in distribution, a conclusion that is just the opposite of that mentioned in the mtDNA paper.

And as mentioned, since the paper was published, I went back to verify one way or the other, my understanding of habitat plus make some searches for the species. You are correct in that the finding of additional specimens in the zone between where the two nearest but different subclade specimens were identified does not disprove Javier's claim of allopatry. But not finding and break in suitable habitat and finding the new specimen provides evidence that the distribution of the species in very likely to be continuous which in turn leads to the likely scenario that there is a zone of intergradation between the two subclades (vs. allopatry).

The finding of 5 specimens by myself and then other specimens found later by Chris Feldman weakens, and virtually discounts the notion contained in the following quote: "These two subclades have completely allopatric distributions, with a break that occurs somewhere in the vicinity of Lassen Volcanic National Park in northeastern California (between the localities of C .b. bottae samples 6 and 14 which lie about 120 (airline) km apart; Fig. 1)."

But without Javier having considered all evidence, I maintain that the claim of allopatry itself was not warranted in the first place. Another way of looking at the situation would be as follows: If the nearest two specimens of different subclades had been 400 km apart, would that be sufficient evidence upon which to make a claim of allopatry? Or, if the two specimens had been 1 km apart, would that evidence support a claim of allopatry? To my way of thinking, the distance between ONLY two samples is meaningless in arriving at a conclusion of allopatry. Just by chance alone, as the distance between specimens increases, the chance of overlap diminishes. By the same token, the claim that a break exists between the two subclades based on only two samples that are 120 km apart is equally flawed. As mentioned, I don't believe the authors gave enough thought to this area of their discussion.

To his credit, on page 233, Javier states, "It is unclear what barriers, if any, presently separate the Sierra Nevada and Northwestern subclades of C. bottae." It is too bad the authors did not check this out as Berkeley (where Javier did this study) is only a couple hundred miles from the Mt. Lassen region. From earlier treatment in the text, one assumes he is referring to barriers of a physical nature. But other barriers might exists. Despite that I consider overlap between the two subclades as being a foregone conclusion, a certain level of 'allopatry' with only marginal overlap could exit if there occurs some type of selection against the survival of hybrids between the two subclades.

I am reminded of just how easy it is to be critical ---- as if I had not made some similar errors in the past (which I have). But having done so, I tend to be more cautious. I suspect that semantics are a bit of a problem as my interpretation may not be what Javier was trying to convey. I agree when you mention, "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."

You go on to mention, "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." At the present time, another mtDNA study is in progress which in addition to rerunning the same samples in the first study, expands the geographical representation of the species and overall sample size. Included are about 10 to 12 new samples where specimens came from nearby or between where samples #6 and #15 were found. Also, there are two samples from the Ruby Mts. in Elko County, Nevada. I am curious as to which subclade will be represented by those two specimens.

I expect that the results will be the same or at least similar to what Javier's paper describes but with perhaps a few different wrinkles. However, without having numerous samples from the Mt. Lassen region, I don't have any great expectations that any new information will emerge.

Richard F. Hoyer


   

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