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Crotalus unicolor (Aruba Island Rs)is considered by the scientific community in general as a species of the genus Crotalus, however quite a few herpetologists seem to disagree with this classification, in fact they support the view that Crotalus unicolor is nothing but a subspecies of the neotropical rattlesnake C. durissus. Does anyone know what are the morphological and/or taxonomic differeces in C. unicolor that would in fact place it as a separate species? Are the subtle differences such as coloration and overall size enough to warrant a specific status? It seems obvious that the reason why they look a bit different is the isolation from the mainland populations of C. durissus (in this case C.d. cumanensis) I'd appreciate any comments fron the experts.
Just curious.....

Thanks a bunch!

Parabuteo

Whether you consider it as a species, a subspecies or a mere colour variant is largely to do with how one defines species. Phylogenetically, the answer is clear, and represented in the mtDNA tree above (from Wüster et al., 2002) - the Aruba Island rattler is a cumanensis that shrank and faded in the wash.

However, some would regard it as a subspecies due to morphological differences (faded pattern, smaller size), and some would regard it as a full species, on the basis that these differences make it diagnosable from other durissus - just as some authors would regard C.v. caliginis as a separate species on these grounds, whereas others would just as vehemently regard it as just an isolated helleri.

Obviously, those who have put a lot of effort into the conservation and captive breeding programmes for the Aruba rattler would probably prefer it to be regarded as a separate species rather than just a colour variety...

Bottom line is, it depends on your personal philosophy of what a species is - I know I wouldn't call it one (and I probably wouldn't even call it a subspecies), but I know plenty who would.

Cheers,

Wolfgang

WÜSTER, W., M.G. SALOMÃO, J.A. QUIJADA-MASCAREÑAS, R.S. THORPE & B.B.B.S.P. (2002) Origin and evolution of the South American pitviper fauna: evidence from mitochondrial DNA sequence analysis. In Biology of the Vipers (G.W. Schuett, M. Höggren, M.E. Douglas & H.W. Greene, eds.), pp. 111-128. Eagle Mountain Publishing, Eagle Mountain, Utah.

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Thanx

???? I don't quite understand (Actually it just strikes me as odd) that C. d. tzabcan had a common ancestor with the "Terrificus group" as opposed to the "Durrisus group"?

Any insight as too why? I guess I'm thinking about them based on range and have this view in my that they should be a derivative of C. d. durissus, UNLESS maybe they all came from a common ancestor and C. d. tzaban, being restricted to the Yucatan, had no pressure from other pitvipers to evolve, thus remained relatively unchanged (Centrifugal speciation?), whereas, C. d. d., and C. d. culminatus were pressured by competition from other pitvipers to evolve ever so slightly but significantly so from C. d. terrificus???? Does that make sense?

Problem is, you ain't seen nuthin' yet - the situation in C. America and Mexico is actualy a good deal more complex than shown in this very preliminary tree - I'll e-mail you about it.

Cheers,

Wolfgang

>>???? I don't quite understand (Actually it just strikes me as odd) that C. d. tzabcan had a common ancestor with the "Terrificus group" as opposed to the "Durrisus group"?
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>> Any insight as too why? I guess I'm thinking about them based on range and have this view in my that they should be a derivative of C. d. durissus, UNLESS maybe they all came from a common ancestor and C. d. tzaban, being restricted to the Yucatan, had no pressure from other pitvipers to evolve, thus remained relatively unchanged (Centrifugal speciation?), whereas, C. d. d., and C. d. culminatus were pressured by competition from other pitvipers to evolve ever so slightly but significantly so from C. d. terrificus???? Does that make sense?
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