First Advisor
Stephen P. Mackessy
First Committee Member
Mit McLaughlin
Second Committee Member
James Haughian
Degree Name
Master of Science
Document Type
Thesis
Date Created
5-2025
Department
College of Natural and Health Sciences, Biological Sciences, Biological Sciences Student Work
Embargo Date
5-2027
Abstract
Venom is a complex mixture of proteins and peptides that has evolved multiple times in animals as an adaptation for prey acquisition and antipredator defense. Snakes are some of the most well-studied venomous animals due to their medical significance towards humans and the fascinating ecological and evolutionary dynamics that have shaped the variation in their toxins. Various mechanisms involving prey defense and other selective pressures have influenced the intra- and interspecific variation of snake venom phenotypes, to the point that a single population may have a profoundly different venom composition relative to its common ancestors. By characterizing the extent of venom variation across a species’ range, one can begin to address how changes in venom composition correlate with differential effects on prey, effects of environment, and diet choice. In this project, I focused on characterizing the range-wide venom variation of the Arizona Black Rattlesnake (Crotalus cerberus), a medically significant pitviper species restricted to the Mogollon Rim and adjacent Sonoran and Mohave deserts of the southwestern United States. While basic venom composition data already exists for this species, its range-wide venom variation remains poorly understood and was the basis for these studies. Our results showed high levels of SVMPs in western and central populations and low levels in eastern populations.
Additionally, samples collected from the westernmost populations of its range (Cerbat and Hualapai Mtns.) show elevated levels of thrombin-like activity. Toxicity assays on NSA inbred mice revealed the species’ venom was significantly more toxic than previously reported. High toxicity coupled with low SVMP activity in the east represents a Type II-like venom phenotype that was not previously found in the earlier research; however, these venoms lack a PLA2-based presynaptic neurotoxin typical of Type II venoms, nor do they contain homologs of myotoxin a, a potent inhibitor of the sarcoplasmic reticulum calcium pump that produces tetanic paralysis in prey. Analyses of enzyme activity as a function of snake body size revealed a positive significant relationship with SVMPs and a negative correlation with kallikrein-like enzymes. Based on RP-HPLC and SDS-PAGE data, venoms display several different venom profiles across the range of C. cerberus. The primary aim of this research project is to determine the biochemical composition of the Arizona Black Rattlesnake’s venom across the entirety of its range. Overall, these analyses will help improve our understanding of the complex evolutionary history and the phenotypic variation of rattlesnake venom and its potential significance to humans in the event of an envenomation.
Abstract Format
html
Language
English
Extent
95 pages
Rights Statement
Copyright is held by the author.
Digital Origin
Born digital
Recommended Citation
Vick, Calvin, "Characterization of Range-wide Venom Variation in the Arizona Black Rattlesnake (Crotalus cerberus)" (2025). Master's Theses. 345.
https://digscholarship.unco.edu/theses/345
