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RE: C. bottae taxonomy

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Posted by: CKing at Fri Apr 18 05:38:25 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  

>>I see this forum is not as lively as it use to be. At any rate, I will pose a problem similar to what I addressed here 2- 3 years ago.
>>I recently came across the following quote. "Subspecies are defunct in modern systematic theory and have no place in current classification! "

That is not so at all. Subspecies are very much in general use. The comment above came obviously from a cladist espousing cladistic dogma. Cladists (taxonomists who adhere to classification convention advocated by Hennig) deal with taxonomic characters. To the cladists, a difference of a single character is evidence of "speciation." Since there is no such thing as a fraction of a character, there is no way for a cladist to recognize subspecies, since the smallest taxnomic unit in their system is the species.

>> Below, I describe the most recent findings regarding the Rubber Boa (Charina bottae) and then pose a question dealing with taxonomy.
>>1) A dwarf form of the Rubber Boa (Charina bottae) has been discovered to occur throughout parts of S. Calif. from the southern tip of the main Sierra Nevada Mts. south about 100 miles to the southern most limits of the species range in the San Jacinto Mts. southeast of Riverside, Calif..
>>North of the extreme southern part of the Sierra Nevada Mts., all other live and preserved Rubber Boa populations that have been examined in California and elsewhere in the species distribution in North America represent the large morph of the species.
>>2) Dwarf morph females and males reach maximum lengths of about 22 inches and 19 1/2 inches respectively. All dwarf populations exhibit relatively low mean ventral and maximum dorsal scale row counts.
>>Large morph females and males examined from preserved material attain lengths of at least 25 and 21 inches respectively. Keep in mind that considerable shrinkage occurs with preservation. From live samples, females of 27 - 30 inches and males of 22 - 24 inches have been recorded. Mean ventral and maximum dorsal scale row counts of the large morph are measurably higher than the dwarf form.
>>3) According to the mtDNA study by Javier Rodriguez-Robles, Glenn Stewart, and Ted Papenfuss, the Rubber Boa is represent by a southern clade and a northern clade which were estimated to have been isolated from one another for 4 - 7 million years. The paper urged the recognition of two species, the Northern Rubber Boa (Charina bottae) and the Southern Rubber Boa (Charina umbratica) representing the two clades.
>>4) The southern clade is composed of just two populations of the dwarf morph that occur in the San Jacinto and San Bernardino Mts. All other populations of the dwarf morph (with both size and scalation features similar to the San Jacinto and San Bernardino populations), along with all populations of the large morph, were assigned to the northern clade.
>>It would appear that a conflict exists between the mtDNA evidence and nuclear DNA (morphological traits) evidence. With or without using subspecific designations, is there anyone that is willing to pose a plausible taxonomic explanation / solution to the situation described above?
>>Richard F. Hoyer (Corvallis, Oregon)
>>P.S. I can post a somewhat more detailed version if anyone believes that might help.

I am familiar with the paper to which you are referring. That paper is a very interesting one, and it shows that the rubber boa probably originated in Southern California, but these southern populations underwent a recent catastrophic event. The few isolated extant populations appear to be derived from a common ancestor quite recently, as the southern populations partially recovered from the catastrophic event of the recent past which must have decimated them.

The northern populations appeared to have migrated out of the south in two separate waves. One of them apparently took the coastal route and went north all the way to Oregon, Washington and also dispersed itself into Utah and other western states. The other wave of migration occurred through the Sierra Nevada Mountains. If I remember the paper correctly, there is no evidence that the coastal migrants ever met the Sierra Nevada migrants. These facts can be gleaned from the mtDNA evidence.

What cannot be determined from the mtDNA evidence is whether the southern boa is a separate species from the northern populations. The authors of the paper you mentioned attempted to use morphological traits to divide the rubber boa into two species, but these traits represent unconvincing evidence of species status. To me, it is best to recognize the southern populations as a subspecies, not a full species. These boas are all derived from a single common ancestor. The two "clades" recognized by Rodriguez-Robles et al. can just as easily be called subclades. Besides, a clade is not a species. In fact, one can call all species of snakes a clade, since a clade is merely defined as a group that includes all of the descendants of a single common ancestor and the common ancestor itself. Hence to synonymize the term species and the term clade is simply untenable.


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