Proposed Re-Classification & ID of North American obsoletus sp.

Ratsnake Info

Written by Sue Knight

Introduction

This guide gives a quick overview of recent classification of North American obsoletus sp. past and present. Traditional distribution map & Burbrink classification distribution map. Also comparitive scale data between the subspecies, length, eye and tongue colour.

North American Ratsnake Distribution

	BLACK RATSNAKE	TEXAS RATSNAKE	GREY RATSNAKE
	Pantherophis obsoletus obsoletus	Pantherophis obsoletus lindheimeri	Pantherophis obsoletus spiloides
Ventrals	222-246	218-238	227-258
Subcaudals	63-90	72-88	70-92
Mid Dorsal	28-27	25-27	25-27
Adult Pattern	28-39 Saddles which may be totally obscured by black pigmentation as the snake matures	25-38 Saddles covering 4-6 dorsal scales each	23-36 Saddles
Juvenile Pattern	28-39 Saddles	Saddles	23-36 Saddles
Tongue	Dark Brown/Black	Dark Brown/Black	Black / Dark Brown
Iris	Darkest Grey/Black	Greyish Brown	Sivery Grey / Dark Grey
Av.Adult Length	120-180cm		90-180cm
Av.Hatch Length	25-35cm	25-35cm	25-35cm


	YELLOW RATSNAKE	GULF HAMMOCK RATSNAKE	DECKERTS RATSNAKE
	Pantherophis obsoletus quadrivittata	Pantherophis obsoletus williamsi	Pantherophis obsoletus deckerti
Ventrals	225-245
Subcaudals	75-102
Mid Dorsal	27-29
Adult Pattern	Four longitudinal stripes 2-3 dorsal scales wide	28-33 Saddles & Four longitudinal stripes	Four longitudinal stripes cover 5-7 dorsal scales
Juvenile Pattern	Saddles		Saddles
Tongue	Black	Black	Black
Iris	Yellowish Orange/Grey	Grey or Greyish Brown	Red / Redish Brown
Av.Adult Length	100-170cm		100-120cm
Av.Hatch Length	25-35cm	25-35cm	25-35cm


	EVERGLADES RATSNAKE	BAIRDS RATSNAKE
	Pantherophis obsoletus rossalleni	Pantherophis bairdi
Ventrals	220-235	234-264
Subcaudals	70-95	81-105
Mid Dorsals	25-27	27
Adult Pattern	Stripes - 1-2 Dorsal Scales wide	Stripes
Juvenile Pattern	Saddles	47-61 Narrow Saddles (2-2.5 Dorsal Scales wide)
Tongue	Red	Deep Red
Iris	Orange	Orange
Av.Adult Length	90-180cm	120-140cm
Av.Hatch Length	25-35cm	25-35cm

2008: Collins & Taggart propose an alternative classification of the New World Ratsnakes. The genus of Pantherophis (Fitzinger 1843) shall consist of these species; guttatus, slowinski & emoryi. The genus Scotophis (Baird & Girard 1853) is to be resurrected for bairdi, obsoletus, alleghaniensis & spiloides. The species catenifer, deppei, lineaticollis, melanoleucus and ruthveni remain in Pituophis (Holbrook, 1842) and a newly described genus, Mintonius (Collins & Taggart 2008), be assigned for vulpinus and gloydi (Fox Snakes).
The proposed alternative reclassification by Collins & Taggart is based on the findings of Burbrink & Lawson (2007) who found that by using two different methods of computer analysis, morphological and characteristic comparisons, plus scutellation testing mitochondrial DNA, that Pituophis was a sister taxon to Pantherophis vulpinus and P. gloydi and were embedded within the Pantherophis clade. According to cladistic rules, systematists aim to reflect monophyletic relationships (those containing all descendants from a single ancestor) rather than paraphyletic relationships (those originating from a single ancestor but omitting some descendants), so the answer was to lump them all into a single genus. Since the genus Pituophis was older than Pantherophis, it took priority and all the recently transferred Pantherophis (Utiger et al) species were dumped into Pituophis.
Now Collins & Taggart looked at this data and thought, Hey! this single genus now needs some tidying up as it's too confusing as it presently stands. We'll take a look at how they live, where they live and their outward appearance and further divide them, knowing the inner make-up of them based on mitochondrial DNA and their various other comparisons given by Burbrink & Lawson to reflect a clearer understanding of their relationship.

2007: Burbrink & Lawson using DNA, placed the genus Pantherophis in synonymy with Pituophis.
The resulting taxonomy for the nine North American species affected would be: Eastern Rat Snake (Pituophis alleghaniensis), Baird's Rat Snake (Pituophis bairdi), Great Plains Rat Snake (Pituophis emoryi), Eastern Fox Snake (Pituophis gloydi), Eastern Corn Snake (Pituophis guttatus), Western Rat Snake (Pituophis obsoletus), Slowinski's Corn Snake (Pituophis slowinskii), Midland Rat Snake (Pituophis spiloides) and Western Fox Snake (Pituophis vulpinus).

2006: Gibbs et al. Using mtDNA sequence data to evaluate the phylogeographic relationships between two of the northernmost populations of black ratsnakes (Pantherophis obsoletus complex) in Ontario, Canada and previously analysed populations in the United States. They then used population-level analyses to evaluate the level of adaptive divergence between previously established mtDNA phylogroups. Phylogenetic analyses show that southern Ontario snakes have mtDNA haplotypes that fall within the Central mtDNA phylogroup, as designated by Burbrink et al. (2000). In contrast, snakes in eastern Ontario carry either Central or Eastern-specific haplotypes. Within the hybrid region, we found highly variable frequencies of mtDNA haplotypes among isolated sub-populations, no association between variation in cytonuclear (mtDNA) and nuclear (microsatellite DNA) markers, no difference in survival or reproductive success among snakes with different mtDNA haplotypes, and no effect of mate similarity in mtDNA on female clutch size. These results argue that the Eastern and Central phylogroups have merged in this region, likely due to a lack of adaptive differentiation between individuals in each lineage. Hence, in these snakes, phylogeographic structure in mtDNA is more a reflection of historical isolation rather than adaptive divergence. The observed reticulation between lineages and lack of evidence for hybrid disgenesis also bears on the classification of these lineages as distinct species.

2003: Crother et al. dismissed the idea of Pantherophis as a separate genera.

2002: Utiger et al. using mtDNA, presented evidence that North American Rat Snakes of the genus Elaphe are a monophyletic lineage different from Old World members of the genus, and resurrected the available name Pantherophis Fitzinger for all North American (north of Mexico) taxa.. With the new genus name Pantherophis also came the gender change on the species, so obsoleta now became obsoletus.

2001: Burbrink published a revision, based on morphological characters, which followed on from an earlier study based on DNA examinations by himself, Lawson & Slowinski
Examination of morphological characters of 1006 specimens of Elaphe bairdi, E. obsoleta obsoleta, E. o. lindheimeri, E. o. spiloides, E. o. williamsi, E. o. quadrivittata, E. o. rossalleni and E. o. deckerti are made. Based on the earlier DNA study and the new morphological results he concludes that the conservation of these taxonomic units has no value, as it is not possible to determine which subspecies an individual belongs to with certainty without knowing the place of origin, because of the variation degree of the subspecies.
He suggested splitting the obsoletus complex into four species based on their DNA and morphology. The four species are as follows:

Elaphe alleghaniensis (Holbrook, 1836)
Proposed new Common name: Eastern Ratsnake
Distribution: East of the Allegheny Mountains: Connecticut, Florida, Georgia, Maryland, New York, North Carolina, Pennsylvania, South Carolina and Virginia, USA.
The species contains the previous subspecies Elaphe obsoleta quadrivittata, E. o. deckerti, E. o. williamsi and E. o. rossalleni.

Elaphe bairdi (Yarrow, 1880)
Distribution: Texas, USA and Coahuila, Nuevo Léon and Tamaulipas, Mexico.
This species has previous been known as Elaphe obsoleta bairdi, but has for quite some years been treated as its own species.

Elaphe obsoleta (Say, 1823)
Proposed new Common name: Western Ratsnake
Distribution: West of the Mississippi: Arkansas, Kansas, Louisiana, Missouri, Nebraska, Oklahoma and Texas, USA, with a single doubtful report from Nuevo Léon, Mexico.
This species has previously been known as Elaphe obsoleta obsoleta and E. o. lindheimeri.

Elaphe spiloides (Duméril, Bibron & Duméril, 1854)
Proposed new Common name: Midlands Ratsnake
Distribution: West of the Apalachicola River and east of the Mississippi, Alabama, Florida, Illinois, Kentucky, Louisiana, Michigan, Mississippi, Ohio, Pennsylvania, Tennessee and Wisconsin, USA.
This species was known as Elaphe obsoleta spiloides.

obsoletus distribution

1977: Olson elevates bairdi to full species status.

1952: Dowling recognises only four subspecies, Elaphe obsoleta obsoleta, E. o. quadrivittata, E. o. lindheimeri and E. o. bairdi. He placed E. o. rossalleni, E. o. deckerti and E. o. williamsi in synonomy with E. o. quadrivittata. E. o. bairdi he considered a subspecies because of it's integration in the wild with E. o. lindheimeri.

1949: Neill describes rossalleni, and lists the following as subspecies, E. o. obsoleta, E. o. confinis (= E. o. spiloides), E. o. williamsi, E o quadrivittata, E. o. rossalleni, E. o. deckerti, and E. o. lindheimeri.

1942: Barbour & Englels describe Elaphe quadrivittata parallela.

1823: Say describes Elaphe obsoleta.

References

1. Burbrink, FT & R. Lawson (2007): How and when did Old World rat snakes disperse into the New World? - Molecular Phylogenetics and Evolution 43 (2007): 173–189.4.
2. Burbrink, F.T. 2001. Systematics of the Eastern Ratsnake Complex (Elaphe obsoleta). Herpetol. Monogr., 15: 1-53
3. Burbrink, F.T., R. Lawson & J.B. Slowinski. 2000. Mitochondrial DNA phylogeography of the North American rat snake (Elaphe obsoleta): a critique of the subspecies concept. Evolution, 54: 2107-2114.
4. Utiger, U., N. Helfenberger, B. Schätti, C. Schmidt, M. Ruf, and V. Ziswiler. 2002. Molecular systematics and phyologeny of Old and New World ratsnakes, Elaphe Auct., and related genera (Reptilia, Squamata, Colubridae). Russian Journal of Herpetology 9:105–124.
5. Gibbs HL, SJ Corey, G Blouin-Demers, KA Prior & PJ Weatherhead. 2006. Hybridization between mtDNA-defined phylogeographic lineages of black ratsnakes (Pantherophis sp.). Molecular Ecology 15: 3755-3767.
6. Dowling, H. G. 1952. A taxonomic status of the rat snakes, genus Elaphe Fitzinger. IV: a check list of the American forms. Occasional Papers of the Museum of Zoology, University of Michigan No. 541. 12pp.
7. Schulz, Klaus-Dieter 1996. A monograph of the colubrid snakes of the genus Elaphe Fitzinger. Koeltz Scientific Books, 439 pp.
8. Wilfred T. Neill. A New Subspecies of Rat Snake (Genus Elaphe), and Notes on Related Forms Herpetologica, Vol. 5,(Jun. 30, 1949), pp. 1-11
9. Crother, B. I., J. Boundy, J. A. Campbell, K. de Quieroz, D. Frost, D. M. Green, R. Highton, J. B. Iverson, R. W. McDiarmid, P. A. Meylan, T. W. Reeder, M. E. Seidel, J. W. Sites, Jr., S. G. Tilley, and D. B. Wake. 2003. Scientific and standard English names of amphibians and reptiles of North America north of Mexico: update. Herpetological Review 34:198-203.
10. Bartlett, R. D. 1993. Comments on the obsoleta-complex rat snakes of Florida. Tropical Fish Hobbyist 41(11):120–122, 124, 126, 128, 130–134, 136–137.
11. Mann A.. A Taxonomic Investigation of the Black Ratsnake in West Virginia using Morphometric Analyses 2008 http://www.marshall.edu/etd/masters/mann-adam-2007-ma.pdf
12. Olson, R. E. 1977. Evidence for the species status of Baird’s ratsnake. Tex. J. Sci. 29:79–84.
13. Barbour, T. & W.L Engels (1942) Two Interesting new Snakes. Proc. New England Zool. 20: 101-104
14. Barbour, Thomas;Carr, F., Jr 1940. Notes on Elaphe and a new species Occasional Papers of the Boston Society of Natural History 8: 337-342
15. Baird, S. F. and C. Girard. 1853. Catalogue of North American Reptiles in the Museum of the Smithsonian Institution. Part 1.-Serpents. Smithsonian Inst., Washington, xvi + 172 pp
16. Say, T. 1823. In James, E. Account of an expedition from Pittsburgh to the Rocky Mountains, performed in the years 1819, '20, by order of the Hon. J. C.
17. Holbrook, John E. 1836. North American Herpetology, Vol. 1 North American Herpetol. Ed.1, Vol. 1
18. Collins, Joseph T. & Taggart, Travis W. 2008, An Alternative Classifiacation of The New World Ratsnakes (Genus Patherophis [Reptilia: Squamata: Colubridae]).

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