Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 29, Number 6;   June, 2002

Pituophis Taxonomy

by Josh Butler

Before we discuss Pituophis, I first must describe the formal and informal processes of taxonomy. Formally, there are two groups that make decisions on the names of species; the American Association of Zoological Nomenclature, which is a satellite-organization for the International Commission on Zoological Nomenclature (ICZN). Generally, if there is a published dispute regarding the name of a species, the authors will present their case to the ICZN, and they will make a ruling based on their established code. However, more typically and informally, once a name sticks, and is used frequently, then the ICZN rarely gets involved. [Ed. Note: The ICZN judges on procedures and does not get involved with species validity - that is the purview of peer reviewed journals.]

For instance, Pituophis melanoleucus has been the most commonly used name for the entire complex; the report I'll be making is only a suggestion. If other authors continue to use the older, more conservative P. melanoleucus and ignore the suggested changes, then P. melanoleucus will not change. However, if authors pick up on the new name, then after time, someone may submit an application to the American Association of Zoological Nomenclature to change the name/s.

This genus is one of the most wide spread and common snakes found in North America with most authors recognizing from a single transcontinental species (the melanoleucus complex, comprised of 15 subspecies) to four (monotypic and polytypic) species (Rodriguez-Robles & De Jesus-Escobar, 2000). Currently, I've found the accepted usage of three North American species, P. melanoleucus, P. catenifer, and P. ruthveni. The mitochondrial DNA work done on this complex recently helped delineate these three species, as well as identifying Pituophis as a monophyletic group (a family derived from a single common ancestor) on top of identifying its nearest colubrid cousins (Rodriguez-Robles, 1999; Rodriguez-Robles & De Jesus-Escobar, 2000).

In English, all western gopher snakes and bullsnakes are lumped into the P. catenifer species, except for P. ruthveni, the Louisiana pine snake. Although it has characteristics of P. melanoleucus and P. catenifer, genetically it looks like it is starting, or in the process of, going down its own evolutionary path. All eastern Pituophis are P. melanoleucus, which includes the subspecies lodingi, melanoleucus, and mugitus. The boundary between the two major clades is the Mississippi River. Additionally, other western species thought to be distinct species were lumped into the catenifer group as well (e.g. vertebralis and bimaris).

So what does that mean for New Mexico? If you consult Degenhardt et al., they use the most conservative taxonomy for P. melanoleucus, using just P. melanoleucus. However their work was published a few years before the current published suggestions. In my opinion, judging from the collection in the Museum of Southwestern Biology, two subspecies predominate; P. catenifer sayi, the Bullsnake, and P. c. affinis, the Sonoran gopher snake. Also, a third subspecies has been reported in New Mexico, P. c. deserticolis, the Great Basin gopher snake.

Recent publications by Werler and Dixon (2000) and Powell et al. (1998) use the new proposed taxonomy.

Bibliography:

Conant, R. & Collins, J.T. 1991. A Field Guide to Reptiles and Amphibians of Eastern/Central North America, 3rd ed. Houghton Mifflin (Boston/New York). xx+450 p.
Powell, R., Collins, J.T., & Errol D. Hooper, Jr. 1998. A Key to the Amphibians and Reptiles of the United States and Canada. University Press of Kansas: Lawrence, Kansas.
Reichling, S. B. 1995. The taxonomic status of the Louisiana pine snake (Pituophis melanoleucus ruthveni) and its relevance to the evolutionary species concept. J. Herpetol., Athens, 29 (2): 186-198.
Rodriguez-Robles, J.A, 1998. Alternative Perspectives on the Diet of Gopher Snakes (Pituophis catenifer, Colubridae): Literature Records versus Stomach Contents of Wild and Museum Specimens. Copeia 1998 (2), 463-466.
Rodriguez-Robles, J.A. 1999. Molecular systematics of New World lampropeltinine snakes (Colubridae): implications for biogeography and evolution of food habits. Biol. J. of the Linn. Soc. 68: 355-385.
Rodriguez-Robles, J.A. & De Jesus-Escobar, J.M. 2000. Molecular Systematics of New World Gopher, Bull, and Pine snakes (Pituophis: Colubridae), a transcontinental Species Complex. Molecular Phylogenetics and Evolution 14(1): 35-50
Stebbins, R.C. 1985. A Field Guide to Western Reptiles and Amphibians, 2nd ed. Houghton Mifflin, Boston.
Werler, John E. and James R. Dixon, 2000. Texas Snakes; Identification, Distribution, and Natural History. University of Texas Press. Austin, Texas, 437p.

KEY TO REVISED PITUOPHIS (bull, pine, or gopher snakes) Adapted from Powell, et al., (1998)

la. Dark line from eye to corner of jaw; Mississippi to Pacific Ocean and south into Mexico P. catenifer lb. No dark line from eye to corner of jaw; solid dark head or light colored head; southeastern United States 2 2a. Dark dorsal blotches run together near head but distinctly separate near tail; eastern Texas to central Louisiana P. ruthveni 2b. Dark dorsal and ventral blotches distinct, or indistinct and obscure, or almost solid black; Kentucky to the East Coast and south to Florida P. melanoleucus