Abstract

Because rattlesnakes rely heavily on their venom for predation and defense, we can expect selection pressures from several sources to act on its composition, including, ontogeny, sex, and environmental variation. In this dissertation, I summarize the results of four studies of the southwestern speckled rattlesnake (Crotalus pyrrhus). First, I describe two cases of envenomation at separate Arizona localities (Tinajas Altas Mountains, Yuma County, and Phoenix Mountains, Maricopa County). Both patients experienced swelling, but neither demonstrated coagulopathy, thrombocytopenia, or hypofibrinogenemia. The latter patient required amputation of the distal portion of his middle finger. I also investigated variation in morphology, diet, and venom protein composition from 23 populations within six biogeographic regions across the species’ United States range of Arizona, California, and Nevada. For morphological variation, snakes varied in in size among biogeographic regions, with the largest snakes occurring in the Mojave Desert, Transverse Ranges, and Peninsular Ranges of California and Nevada; the smallest snakes restricted to the Lower Colorado River subdivision of the Sonoran Desert; and snakes of intermediate size inhabiting the Colorado Desert (California) and Arizona Uplands subdivision of the Sonoran Desert. I also documented sexual body component dimorphism, with females possessing larger heads and longer trunks than males relative to overall body size. The diet of C. pyrrhus consisted predominately of mammals (80.8%), in particular terrestrial squirrels (39.4%) and the heteromyid rodent genus Chaetodipus (26.9%). An ontogenetic shift occurred from primarily lizards to rodents, but neither biogeographic region nor sex significantly influenced prey class consumed. However, the Tinajas Altas Mountains population apparently relies on birds to a greater extent than other populations. For venom composition, I used reverse-phase liquid chromatography and mass spectrometry to define eight elution regions, each dominated by one to three protein families. Seven elution regions varied among the biogeographic regions and three by sex. The biggest distinction was between venoms of eastern (Arizona) and western (California/Nevada) snakes. We failed to detect Mojave Toxin (or a homolog) in any population. Collectively, these findings document differences in phenotypic and behavioral traits of C. pyrrhus and suggest that variable fitness landscapes provide different fitness optima.

LLU Discipline

Biology

Department

Biology

School

School of Medicine

First Advisor

William K. Hayes

Second Advisor

Leonard Brand

Third Advisor

Allen Cooper

Fifth Advisor

Bryan Grieg Fry

Sixth Advisor

Timothy Standish

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

2019

Date (Title Page)

6-2019

Language

English

Library of Congress/MESH Subject Headings

Rattlesnakes--Venom; Rattlesnakes--Southwestern States--Identification.

Type

Dissertation

Page Count

xvii, 159 p.

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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