Date of Award


Document Type


Degree Name

Master of Science (MS)


Biological Sciences

Committee Chair/Advisor

Christopher L. Parkinson

Committee Member

Vincent Richards

Committee Member

Christopher Saski


Crotoxin and its homologs (hereafter all referred to as CTx) is a highly lethal heterodimeric beta-neurotoxin found in pitvipers (Crotalinae) and is the main driver of neurotoxic venom phenotypes (Type II). In contrast, hemorrhagic venom phenotypes (Type I) are characterized by high snake venom metalloproteinase expression and low toxicity. Although many rattlesnake species have been classified as either Type I or Type II, population level variation in venom phenotype has also been documented in several species. The presence or absence of CTx is the main component of this variation in venom phenotype and has been most widely studied in large-bodied lowland rattlesnakes (Crotalus scutulatus, C. helleri, and C. horridus). While it has been suspected to be in C. lepidus, a small-bodied montane rattlesnake, there has been no genetic confirmation. We used genomics and transcriptomics to test for the presence, distribution, and evolution of CTx in C. lepidus. We genomically and transcriptomically confirmed the presence and expression of CTx in C. lepidus and found it in 17 out of 104 samples across their range. CTx presence was not significantly associated with longitude, latitude, subspecies, or elevation. However, we did identify several climatic variables associated with CTx presence, including ones that have been identified in previous studies on CTx expression providing insights on the phylogenetic distribution of CTx across rattlesnakes, the variation in crotoxin expression, and highlighting environments to which CTx may be locally adapted. Our results likely support previous hypotheses of an ancestral origin for crotoxin followed by independent sorting in lineages; therefore, future studies should focus on testing for the presence of CTx in other species of montane rattlesnakes.

Included in

Biology Commons



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.