First Advisor

Mackessy, Stephen

First Committee Member

James, Andrea

Second Committee Member

Haughian, James

Third Committee Member

Apawu, Aaron

Degree Name

Doctor of Philosophy

Document Type


Date Created



College of Natural and Health Sciences, Biological Sciences, Biological Sciences Student Work

Embargo Date



Snake venoms can show a large degree of phenotypic variation based on factors such as geographic location, environmental influences, and age which is likely beneficial for local adaptations to various ecological niches. Venom composition not only affects the ability of a snake to acquire prey but can also impact snakebite symptomology. This study, involving sixty-seven individual Great Basin Rattlesnake (Crotalus oreganus lutosus) venom samples collected from Idaho, Utah, California, and Arizona, showed that ontogenetic and geographic variables play a significant role and clearly drive the variation found within the venom of the Great Basin Rattlesnake. All six toxin families assessed showed ontogenetic shifts to varying degrees, with some trends differing from those observed in other rattlesnake species, suggesting species-specific ontogenetic patterns. Geographic trends were also observed, with snake venom metalloproteinase (SVMP) and thrombin-like serine proteinase activity showing a positive linear relationship with latitude while L-amino acid oxidase activity showed a negative linear relationship. Additionally, the presence of clustering for high or low toxin activities suggests the presence of metapopulations. This study shows that there are multiple ontogenetic patterns that can occur among rattlesnakes and that the determinants of range wide venom compositional variation are multifactorial. To investigate further and gain a better understanding of the utility of such variation and the factors that may drive it, this study further focused on the SVMPs found in C. o. lutosus venom. With SVMPs making up a major portion of rattlesnake venoms, they are necessary components for incapacitating prey, and also play a large role in the pathologies associated with viperid envenomations. This study characterizes three SVMPs, presumably a P-I, P-II, and P-III, isolated from the venom of the Great Basin Rattlesnake. All SVMPs were hemorrhagic with the P-III being five-times more hemorrhagic than the others. They were all alpha-fibrinogenolytic, with the P-II and P-III also cleaving the beta-chain of fibrinogen. These properties have broad consequences in the case of envenomation, both allowing the venom toxins to spread more readily. Significant variation was observed in the sensitivities of the three classes of SVMPs to two tripeptide inhibitors: P-III was clearly the most affected by both pENW and pEQW, while P-II and P-I showed little effect of these inhibitors on proteolytic activity, indicating possible differences in the storage mechanisms for these toxins. There was also significant variability when assessing the degree of inhibition exerted by human α2M on SVMP proteolytic activity at a 2:1 molar ratio of inhibitor to toxin with an 84.4% reduction for P-I, 83.5% reduction for P-II, and 50.4% reduction for P-III. All showed evidence of α2M bait region cleavage. Additionally, all three SVMPs showed significant reduction in HUVEC cell viability in vitro with P-I proving the most cytotoxic, likely in part due to increased interference with cell adhesion. The variation in terms of substrate specificity, inhibition, and their effects on endothelial cell viability in vitro leads to a culmination of both local and systemic damage, thus contributing significantly to the effectiveness of the venom in rapidly debilitating prey, and this variation can also be useful in manifesting a venom that can be effective on a variety of prey species. The characterization of C. o. lutosus venom, and particularly these three hemorrhagic SVMPs, may help provide a better understanding of pathologies induced by the various venom components and their associated clinical manifestations. This work highlights the remarkable utility of having an arsenal of toxins with varying activities and specificities to target a variety of prey and also surmount a multifaceted attack on an individual prey item.

Abstract Format



131 pages

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Copyright is held by the author.

Available for download on Tuesday, May 13, 2025