Subspecific classification of Sistrurus tergeminus in Colorado 

Montgomery, Chad E.

chadmont@truman.edu

Department of Agricultural and Biological Sciences

Truman State University

 Kirksville, Missouri USA

Hobert, Justin

Denver, Colorado USA

Mackessy, Stephen P.

School of Biological Sciences

University of Northern Colorado

Greeley, Colorado USA

The classification of the Massasauga Rattlesnake, Sistrurus tergeminus, in Colorado is contentious.  Historically, populations of S. tergeminus in Colorado have been allocated to the Plains Massasauga, S. t. tergeminus, the Desert Massasauga, S. t. edwardsii, or an intergrade form. We used venom and scutellation characteristics of known individuals of S. catenatus, S. t. tergeminus, and S. t. edwardsii to specimens from Colorado to determine the taxonomic classification of S. tergeminus in Colorado. We performed discriminant function analysis (DFA) and principal component analysis (PCA) using nine scale counts and two pattern characters and characterized venom protein composition to determine the overall similarity of the Colorado S. tergeminus to the two geographically closest subspecies, S. t. edwardsii and S. t. tergeminus. Based on venom protein composition and scutellation characteristics Colorado S. tergeminus are more closely aligned with S. t. edwardsii rather than S. t. tergeminus or an intergrade form.