NEWS RELEASE
The Center for North American Herpetology
Lawrence, Kansas
http://www.cnah.org
1 August 2008

DEMOGRAPHIC AND PHYLOGEOGRAPHIC HISTORIES OF TWO VENOMOUS NORTH
AMERICAN SNAKES OF THE GENUS AGKISTRODON

Timothy J. Guiher and Frank T. Burbrink

2008. Molecular Phylogenetics and Evolution 48(2): 543-553

Abstract: Many studies have revealed that lineages currently inhabiting formerly glaciated
areas were pushed into southern glacial refugia and have expanded into their modern
range since the last glacial maximum. There have been few studies that compare the
effects of glacial cycles on lineage diversification and historical demography in closely
related species with overlapping ranges. In this study we compare phylogeographic
structure, historical demography, and approximate lineage age in two closely related and
broadly co-occurring venomous snakes in eastern North America, the Cottonmouth
(Agkistrodon piscivorus) and Copperhead (A. contortrix), using sequences from the mtDNA
gene cytochrome b. We inferred three geographic lineages of A. contortrix and two of A.
piscivorus with no common geographic or temporal pattern of lineage diversification
identified for these species. Lineage diversification occurred in the Late Pliocene for A.
piscivorus (2.5 mya) and in the Early Pleistocene for A. contortrix (1.5 mya). Demographic
estimates revealed population expansion following the last glacial maximum (20,000 years
ago) in two lineages of A. contortrix (the Central clade and Eastern clade) and one lineage
of A. piscivorus (the Continental clade). The Florida clade of A. piscivorus is the only
lineage for which constant population size through time was inferred, possibly due to
stable populations persisting in areas unaffected by glacial advances. Our data suggest
that unique habitat preferences may have shaped both the phylogeographic and
demographic histories of each species.

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CNAH Note: Using mtDNA, Guiher & Burbrink (2008) identified three evolutionary lineages
of Agkistrodon contortrix and two evolutionary lineages of Agkistrodon piscivorus in this
excellent paper, but did not name them as distinct species, instead awaiting future results
of analysis of nucleic DNA evidence. However, based on known type localities (as they
appear in Gloyd & Conant, 1990, and Schmidt, 1953) for already described, published, and
available names, the following distinct species might be recognized in the future:

Agkistrodon contortrix Linnaeus, 1766 (Eastern lineage of Guiher & Burbrink 2008)
Type locality: Charleston, South Carolina
Standard common name would become: Eastern Copperhead
Synonym: Agkistrodon contortrix mokasen Palisot de Beauvois, 1799

Agkistrodon austrinus Gloyd & Conant, 1943 (Central lineage of Guiher & Burbrink 2008)
Type locality: Orleans Parish, Louisiana
Standard common name would become: Midland Copperhead
Synonyms: none

Agkistrodon laticinctus Gloyd & Conant, 1934 (Western lineage of Guiher & Burbrink 2008)
Type locality: Bexar County, Texas
Standard common name would become: Western Copperhead
Synonyms: Agkistrodon contortrix phaeogaster Gloyd, 1969; Agkistrodon contortrix
pictigaster Gloyd & Conant, 1943

Agkistrodon piscivorus Lacépède, 1789 (Continental lineage of Guiher & Burbrink 2008)
Type locality: Charleston, South Carolina
Standard common name would become: Northern Cottonmouth
Synonyms: Agkistrodon piscivorus leucostoma Troost, 1836; Toxicophis pugnax Baird &
Girard, 1853

Agkistrodon conanti Gloyd, 1969 (Florida lineage of Guiher & Burbrink 2008)
Type locality: Alachua County, Florida
Standard common name would become: Southern Cottonmouth
Synonyms: none

The above list of name combinations is presented here merely as advance information of
possible future changes in the taxonomy of two polytypic species of the North American
genus Agkistrodon. Under no circumstances should the above list be adopted as a
taxonomy for the group. Additional work on the systematics of these serpents is in
progress.

References

Gloyd, Howard K. and Roger Conant. 1990. Snakes of the Agkistrodon Complex. A
Monographic Review. SSAR Contribution to Herpetology 6: vi + 614 pp.

Schmidt, Karl P. 1953. A check list of North American amphibians and reptiles. Sixth Ed.
Publ. American Soc. Ich. Herp., viii + 280 pp.

Joseph T. Collins
Director
CNAH