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RE: Rubber Boa and Rosy Boa

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Posted by: CKing at Sat Jun 28 00:38:28 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  
   

>>CK,
>>Thanks for the explanation but due to my lack of background, it is still not all that clear.>>

I presume you mean my explanation of paraphyletic taxa. It is, as I said, an important concept since a vast majority of the taxonomic proposals are based on the cladists’ intolerance of paraphyletic taxa. For example, such recent changes as the transfer of Hyla regilla to Pseudacris, the splitting of Clemmys into several different genera, the resurrection of Pantherophis for N. American species of Elaphe, and the recently proposed lumping of N. American species of Elaphe with Pituophis are all examples of the cladists’ intolerance of paraphyletic taxa.

Basically a paraphyletic taxon is one in which some of the descendants of the common ancestor of that taxon have been excluded. For example, Reptilia (as traditionally defined) is paraphyletic (according to the cladists) because the common ancestor of Reptilia also gave rise to mammals and birds, which are traditionally classified in Mammalia and Aves respectively. The taxon Aves, however, is not considered paraphyletic by the cladists because as far as we know, no species that has evolved from the common ancestor of the birds has been excluded from Aves. Darwinians make no distinction between paraphyletic and monophyletic taxa, but the cladists do. This is why there is often big controversies when there are new taxonomic proposals made on the basis of the cladistic intolerance of paraphyletic taxa (e.g. the proposed split of Iguanidae into several different families a little over a decade ago).

>>There is one large disconnect in our thinking regarding C. bottle distribution when you mention, "At the time of Rodriguez-Robles et al.’s paper, there was indeed a break in the distribution of the rubber boa in the vicinity of Lassen National Park.">>

According to scientific data available at the time of Rodriguez-Robles’s paper, there was a break in the distribution of C. bottae. As you know very well, scientists can only base their conclusion on the available data, although you also know very well that this is not always the case. When there is new data, revisions to the existing theory should be made if necessary, although you also know very well that it is not always done.

>>The notion that a break existed in the distribution of the species in the Mt. Lassen region at the time of Javier' study is not rational but was due to a lack of available finer scale sampling. In other words, the authors reached an erroneous conclusion simply because tissue was only available from boas that occurred at considerable distance from one another. If the only tissue available had been from vouchers near Mt Hood in Oregon and Lake Tahoe, it would be just as irrational to claim that a break in the distribution of the species exists from near Mt. Hood to Lake Tahoe.>>

With hindsight, it is clear that Rodriguez-Robles et al. reached an incorrect conclusion concerning the existence of the break in distribution. However, they did follow scientific procedure in basing their conclusion only on the available data.

>>So as they do not repeat the same error, I have already mentioned to Glenn and Rick that they need to exercise caution when making interpretations where large gaps exist between related haplotypes because the tendency is conclude that such a gaps are real. An equal or even more likely explanation is that such gaps are due to short comings in sampling as was the case in Javier's study.>>

To your credit, your prediction that the break is due to lack of collection is correct. However, as you pointed out in one of your papers, rubber boas are extremely difficult to find, even for experts. Therefore, it is understandable how there can be no samples from the area surrounding Lassen National Park until the recent past.

>>I recently received a copy of the MP consensus tree for the new mtDNA study. On a large scale, the result duplicate and confirm Javier's results of three major groupings or subclades. On a finer scale, there occurs some new results that conflict with conclusions reached by Javier. But that is to be expect in research and it will be of interest how these new results are interpreted.
>>
>>Richard F. Hoyer

Thanks. As far as I can tell, Rodriguez-Robles’ several mtDNA based studies are quite reliable. Overall he did a very good job of sampling. Since you are apparently unable to reveal more of the results, I will await its publication and see if I agree with the new interpretation. BTW, I notice that recently there has been a publication of mtDNA data of the rosy boa. I have good reason to believe that the rosy boa probably budded from a small population of the rubber boa. Osteologically the two species are nearly indistinguishable (according to the paleontologists who compared their vertebra), and these two species have complementary but non-overlapping ranges. This is almost a classic case of budding, in which environmental changes isolated two populations of the same species, with subsequent divergent evolution of one of these populations while the parental population remains relatively unchanged.

It would be interesting if the mtDNA of both species are combined in a single phylogenetic analysis. It may indeed show that the rosy boa budded from the rubber boa. If so, then the rubber boa would be paraphyletic, because all of the descendants of the last common ancestor of rubber boa would not be included in C. bottae, since some of the descendants are now in L. trivirgata. Of course that would drive the cladists nuts, and they may splinter C. bottae into several different species, just as Shaffer et al. had separated Ambystoma tigrinum californiense from A. trigrinum primarily on the basis of an intolerance of paraphyletic taxa.


   

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