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RE: C. bottae taxonomy

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Posted by: CKing at Sat Apr 19 05:38:29 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  

>>Thanks for your response. And by the way, the species involved is the Rubber Boa and not the Rosy Boa.
>>I have posed this same question elsewhere. So far, no one has even attempted a response let alone pose a solution either with or without the use of subspecific designations. So you stand alone in providing some input and that is appreciated.
>>At times, I have found myself agreeing with Ron Nussbaum who in a 1974 paper on the species, discarded the then 3 recognized subspecies and simply lumped all Rubber Boas into a single species. Yet that arrangement overlooks the present situation (unknown at that time) where there are two discernable groupings of the species. On the one hand, there is the large morph populations characterized by large size, relatively high ventral and dorsal scale row count. In contrast, there are the dwarf morph populations all characterized by small size and with relatively lower ventral and dorsal scale row counts.
>>In addition, these two groupings are clustered geographically. Had such information been available in bygone years, the two groups would either have been designated as subspecies or species. However, the present mtDNA results throws a monkey wrench into that scenario. At the present, I can think of two explanation that might tend to be consistent with the mtDNA results.
>>1) One might argue for retention of the two species, the Southern Rubber Boa and Northern Rubber Boa with the latter being composed of two subspecies as follows: All large morph populations would comprise a northern subspecies and all other dwarf populations (expect those in the San Bernardino and San Jacinto Mts.) would constitute a southwestern subspecies of the Northern Rubber Boa.

That is an untenable arrangement on the basis of mtDNA data. The two populations in the north that are characterized by large size represent two different waves of migrations from the south. These two populations are not known to interbreed. Rodriguez-Robles et al. pointed this out in their paper:

"...the Sierra Nevada and the Northwestern 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)."

Because of allopatry, there is the possibility (albeit remote) that these two distinct lineages may not even be able to interbreed with each other. In that case they could be considered distinct species. Their large body sizes may have evolved convergently (because of similar environmental conditions) or through parallel evolution (because of the independent expression of the same gene that is inherited from their common ancestor). Hence this particular similarity alone cannot be used to group them as a single species or even subspecies until further study. If it is parallelism which is responsible for their large body sizes, then they can be considered the same subspecies or species provided that they can interbreed.

>>2) A second scenario would be to have three subspecies. All large morph populations would belong to the northern subspecies, the dwarf populations in the San Bernardino and San Jacinto Mts. would belong to a southeastern subspecies, and all other dwarf population in S. Calif. would belong to a southwestern subspecies.

This arrangement is also not tenable. Personally, I would group the dwarf boas in Kern County with the umbratica subspecies to the south, and divide the two northern lineages as separate subspecies for the time being. I am assuming that dwarfism is an ancestral condition (which seems very likely) and that the Kern County animals have retained this ancestral condition. If dwarfism is indeed ancestral, then the two allopatric populations to the north almost certainly evolved their large body sizes independently of each other and therefore they should not be lumped together as a single subspecies because of morphological similarities that are likely convergent.

>>Of course, the problem with both scenarios is that they disregard the current vogue of discarding all subspecific designations. I am not knowledgeable enough about how to interpret mtDNA results but the data presented in Javier's paper might suggest additional scenarios as well.

We can safely disregard the philosophical aversion to the subspecies category exhibited by many cladists. The cladists embrace a classification philosophy that is unique to themselves and their philosophy has contributed much to the chaos we see today in taxonomy.

>>I did not post the longer explanation which indicates all Rubber Boas populations occupy the identical ecological niche regardless of geography. They are all nest robbers mostly preying on small mammal nestlings (shrews, moles, mice, gophers, voles, rats, etc.) Secondly, I have already completed some crosses between dwarf and large morph specimens and size is definitely under genetic control. In addition, maintaining juvenile and subadult specimens of both size morphs under identical laboratory conditions substantiates that size is genetically controlled and not a function of differing environmental conditions.

If dwarfism is under genetic control, then it is all the more reason not to lump the two allopatric large morph populations to the north as a single taxon. Have you tried hybridizing the coastal boas with the large morph Sierra Nevada boas? If the hybrids are infertile or if they refuse to mate, we may well have two different species. If their large body sizes are under the control of different genes, then there is a possibility that at least some of the hybrids could exhibit the ancestral state of dwarfism. The rubber boa is a very interesting species indeed.


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