Elaphe obsoleta

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Elaphe obsoleta

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Reptilia
Order:	Squamata
Suborder:	Serpentes
Family:	Colubridae
Genus:	Elaphe
Species:	E. obsoleta

Binomial name

Elaphe obsoleta
(Say In James, 1823)

Common names: black rat snake, pilot black snake, black snake.^[1]

Elaphe obsoleta is a non-venomous colubrid species found in North America. It prefers heavily wooded areas and they are known for having excellent climbing ability, including the ability to climb the trunk of large mature trees without the aid of branches. No subspecies are currently recognized.^[2]

1 Description
2 Taxonomic issues
3 Photo gallery
4 Cited references
5 External links

[edit] Description

This species is a constrictor, meaning it suffocates its prey, coiling around small animals and tightening its grip until they can no longer draw breath, before eating them. (The process of constriction.) Though they do consume mice and rats, the Black Rat Snakes also willingly consume chipmunks, squirrels, birds, and bird eggs. In captivity, they have a reputation for being "vacuum cleaners," and will eat almost anything placed in front of them.

Adults can become quite large and are known to reach up to eight (8) feet, being the largest snake found in Canada. The record length for a Black Rat Snake is 101 inches, making it (officially) the largest snake in North America. Unofficially, Indigo Snakes are known to exceed them, and one wild caught Pine Snake with a portion of its tail missing measured 111 inches.

When spotted by humans, Black Rat Snakes may freeze and wrinkle themselves into a series of kinks. Black Rat Snakes are usually non-aggressive, but will often strike at the hand of anyone who tries to capture them. They are non-venomous, but can inflict a fairly painful bite.

[edit] Taxonomic issues

There are recent proposed, but not universally accepted, taxonomic changes for this species and the other North American members of Elaphe (suggested Pantherophis). Some taxonomists have suggested splitting what is now Elaphe obsoleta (suggested P. obsoletus) into three geographically separate species:

Pantherophis alleghaniensis, Eastern Rat Snake. Range: east of Allegheny Mountains
Pantherophis aspiloides, Midland Rat Snake. Range: west of Apalachicola River and east of the Mississippi River
Pantherophis obsoletus, Western Rat Snake. Range: west of the Mississippi River

Under this scheme, the color variations (Black Rat Snake, Yellow Rat Snake, Grey Rat Snake) do not correspond to subspecies. The color phases are considered to be a clinal variation in pigmentation with latitude or other climatic factors.

It should be noted that while a taxonomic suggestion has been made to change the genus Elaphe to Pantherophis, and this suggestion has been taken up by the web community at large, most herpetologists do not accept the suggestion and Herpetological Review 2003 34(3) rejected the taxonomic change. Several arguments against the change concerns the type of analysis used and the concept of "species" in biology.

The Russian study that suggested the Old World and New World rat snakes were statistically significantly different was based off of mitochondrial DNA evidence, not nuclear DNA.
According to the concept of a species that is most commonly used in biology, if two populations can interbreed and produce viable, fertile and ecologically functional offspring, the two populations are the same species. Under this definition hybrids are, by definition, sterile and the product of crossing different species (at least). This genetic compatibility is based on nuclear DNA (nDNA). Mitochondrial DNA (mDNA) has nothing to do with compatiblity of genomes and thus the functioning of a group as a single or multiple species.
Since the mitochondrion is of bacterial origin (its chromosome is a single, circular chromosome like a bacterial chromosome) and lacks much of the proof reading apparatus found in the nucleus, it has a much higher mutation rate than nDNA. As long as the cytochrome system and the ATP generation apparatus still function, mutations in mitochondria can abound with little detriment to the cell. Thus wide diversity in mitochondrial sequences may be found while nDNA sequences may not be nearly as diverse.
Since, in nature, biological species are most readily recognized by their ability to reproduce with each other, and that is a function of nDNA compatibility, examination of mDNA is useful to determine separation of populations, but not speciation since the mitochondria are not needed for genetic compatibility.
Since the Russian study used mDNA instead of nDNA no relevance to the reproductive and nuclear genetic relatedness of the genera can be inferred from the data.

These references discuss some of the taxonomic issues.