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RE: C. bottae taxonomy

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Posted by: CKing at Fri May 16 19:50:14 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  

>>Conjecture and other forms of speculation are commonly included in the 'Discussion' sections of published accounts.>>

I agree with that absolutely.

>>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.>>

Sample size will always be a source of disagreement. Of course a larger sample size is better. Keep in mind, however, that Rodriguez-Robles' mtDNA data represented the first investigation of this kind on the rubber boa. They do not have the foresight of available data to guide them as to where they should sample and how large a sample they should have. Overall I think they did a very good job of picking their samples. In a similar case, it was shown, using human x chromosome markers, that the first wave of human migration out of Africa went straight to Australia. However, there is no genetic evidence in the first investigations to show that the Australian lineage left its traces in Asia, which is located between Africa and Australia. Despite the lack of evidence, Spencer Wells, a Stanford geneticist, went to south India and obtained DNA samples from a remote village where it is thought that genetic evidence may be preserved without being swamped by later waves of human migration from the Middle East. And he succeeded. He found genetic evidence of the Australian lineage in this small Indian village. Similarly, it is possible, with additional sampling, to show that the allopatry conclusion may be false. But it will take genetic evidence to refute Rodriguez-Robles' claim of allopatry, the same sort of evidence that Spencer Wells took pains to gather.

>>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.>>

I understand your objection to Rodriguez-Robles' conclusion, and I agree that the sample size may not have been large enough to justify his conclusion. Nevertheless, his conclusion is based on the available data, and it is a logical conclusion. It will take more than reasoned arguments to falsify his conclusion. It will take contradictory mtDNA data. It will take a herpetological equivalent of Spencer Wells to gather the data to either prove or disprove Rodriguez-Robles.

>>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. >>

If you draw a range map using the available mtDNA data, the two subclades are in fact allopatric. You may believe that the mtDNA data is inadequate, but Rodriguez-Robles did base their conclusion on the data they have on hand. Of course better data may well overturn their conclusion, but then again it may not.

>>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). >>

Yes, I agree that the zone of intergradation is possible, and perhaps even probable. But the difficulty in accepting it as real is the lack of supporting mtDNA data.

>>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)." >>

It would be great if we can determine the mtDNA haplotypes of these new speciments. That would help in settling the controversy perhaps.

>>But without Javier having considered all evidence, I maintain that the claim of allopatry itself was not warranted in the first place. >>

I have to disagree with you here. Rodriguez-Robles' conclusion is solidly grounded on the available evidence to them. New evidence may have surfaced since their conclusion which may or may not falsify their conclusion. But so far I have not seen any evidence that could falsify the allopatry theory.

>>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.>>

You are correct that Rodriguez-Robles may have erred in their conclusion, and they may in fact have not thought about the possibility that the two subclades may in fact have met. However, anyone who disagrees with their conclusion is free to falsify it with mtDNA data. There is a similar controversy as to whether the Mt. Hamilton specimen of Lampropeltis zonata is an intergrade between L. z. multifasciata and L. z. zonata. Guess what? mtDNA evidence shows that it is instead a member of L. z. multicincta. So, the availability of mtDNA data can often help settle endless arguments.

>>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 know you feel strongly that the claimed allopatry is not real. And in fact you may well be correct. However, science relies on evidence, so it must take evidence, in the form of mtDNA data, to show that your theory is correct.

>>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.>>

Wonderful news! The new data hopefully will resolve the controversy. Based on the old data, the Nevada specimens are almost certainly going to belong to the Northwestern subclade, i.e. more closely related to boas from Berkeley than to boas from the geographically closer Sierra Nevada Mountain Range.

>>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

Perhaps you can give the investigators some input as to your concerns. Hopefully they can include more samples near the area of supposed allopatry. If a snake with the mtDNA haplotype of the Northwestern subclade is found within the known range of the Sierra Nevada subclade or vice versa, then allopatry is disproven. For the time being, the available evidence is consistent with the theory of complete allopatry.



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