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TAXONOMIC NOTES


Pantherophis guttatus (Corn Snake) complex


We propose that the most conservative approach toward the taxonomy of this group is that of a single widespread polytypic species (P. guttatus) with four locally distinct subspecies in the southwestern region of the United States. It has become increasingly apparent that the once-perceived distributional hiatus [e.g., Wright and Wright (1957), Conant, (1958)] between guttatus and emoryi types does not exist. In fact, snakes from the “hiatus” (east-central Texas, southeastern Oklahoma, and southern Arkansas) may be difficult to assign to either “guttatus” or “emoryi” types, a situation, in our opinion, more indicative of intergrading subspecies than of reproductively isolated species.

Recent evaluation of this complex via mitochondrial DNA sequencing (Burbrink, 2002) has produced a phylogenetic tree the results of which could equally well be interpreted to represent subspecies rather than the author’s preferred full species scenario.

At any rate, we do not feel that the mtDNA sequencing methodology alone (which evaluates characters not directly subject to natural selection) should automatically trump traditional morphological methods (which deal with characters that are unquestionably subject to natural selection). Ideally, when molecular methods disagree with more intuitive traditional procedures, we feel that the most conservative evaluation should be adopted or maintained until such discordances can be reconciled, preferably by a synthesis involving all applicable taxonomic techniques.

Pantherophis guttatus emoryi (Great Plains Ratsnake) – We follow Werler and Dixon (2000) and Dixon and Werler (2005) in their interpretation of the subspecific relationships of these snakes in the southwestern region. Its southern limit, the Balcones Escarpment, along which it intergrades with the Tamualipan form meahllmorum, conforms to well-established zoogeographical patterns in south-central Texas.

Pantherophis guttatus intermontanus (Intermountain Ratsnake) – First described by Woodbury and Woodbury (1942) on the basis of a lighter coloration, smaller size, reduced scutellation numbers, and increased blotch counts, this subspecies was sunk by Dowling (1952) who was followed by most subsequent authors, including the influential national checklist author Schmidt (1953). Many avocational herpetologists, however, have long maintained that this population is highly distinct (Schulz, 1996) and, given its isolated distribution, we feel that it should be accorded taxonomic recognition. Indeed, it is somewhat surprising that advocates of the Evolutionary Species Concept (e.g., Collins, 1991) have not yet proposed full species status for this taxon.

Pantherophis guttatus meahllmorum (Thornscrub Ratsnake) – We follow Werler and Dixon (2000) and Dixon and Werler (2005) in their interpretation of the subspecific relationships of these snakes in the southwestern region. Additionally, we propose that the distribution and habitat of this subspecies, characteristic of the Tamualipan Biotic Province, is better described by the common name “Thornscrub Ratsnake” than by the more vague “Southwestern Ratsnake.”

Pantherophis guttatus slowinskii (Slowinski’s Corn Snake) – Long known to hobbyists as the “Kisatchie Corn Snake,” this taxon was described by Burbrink (2002) as a full species on the basis of a phylogenetic tree derived from mitochondrial DNA sequencing. We concur that slowinskii is a valid taxon but, in view of the manner in which it appears to seamlessly morph into emoryi and meahllmorum to the west, we feel that its recognition at the subspecific level better agrees with currently available data.

Literature Cited

Burbrink, F.T. 2002. Phylogeographic analysis of the corn snake (Elaphe guttata) complex as inferred from maximum likelihood and Bayesian analyses. Molecular Phylogenetics and Evolution 25 (2002): 465-476.

Conant, R. 1958. A field guide to reptiles and amphibians of the United States and Canada east of the 100th meridian. Boston: Houghton Mifflin Co.

Collins, J.T. 1991. Viewpoint: a new taxonomic arrangement for some North American amphibians and reptiles. Herp. Rev. 22(2): 42-43.

Dixon, J.R. and J.E. Werler. 2005. Texas Snakes: A Field Guide. Austin: University of Texas Press.

Dowling, H.G. 1952. A taxonomic study of the ratsnakes, genus Elaphe Fitzinger. IV. A checklist of the American forms. Occas. Pap. Mus. Zool. Univ. Mich. 541: 1-12.

Schulz, K.D. 1996. A Monograph of the Colubrid Snakes of the Genus Elaphe. Havlickruv Brod., Czech Republic: Koeltz Scientific Books.

Schmidt, K.P. 1953. A checklist of North American amphibians and reptiles. Chicago: University of Chicago Press.

Werler, J.E. and J.R. Dixon. 2000. Texas Snakes: Identification, Distribution and Natural History. Austin: University of Texas Press

Woodbury, A.H. and D.M. Woodbury. 1942. Studies of the rat snake, Elaphe laeta, with description of a new subspecies. Proc. Biol. Soc. Washington 55: 133-142.

Wright, A. H., and A. A. Wright. 1957. Handbook of snakes of the United States and Canada. Ithaca, N. Y.: Comstock Publishing Co.


20 Jul 2009

SWCHR Committee on Common and Scientific Names
Tom Lott, Committee Chair
Terry Cox
Riley J. Campbell


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