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Mackessy, Stephen

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Biochemical ecology examines the complex and dynamic relationships between organisms and their environment from a molecular perspective. This requires a holistic integration of ecology, evolution, and natural history with the fine-scale resolution of molecular biology and functional biochemistry. Venomous snakes have evolved a wide variety of extreme behavioral, physiological, and biochemical adaptations for prey capture, making them an ideal model for the study of predator trait evolution and protein adaptation. However, venoms must be understood from an ecological perspective in order to comprehend the evolutionary forces that shape the diversity of toxin families present in venoms. This holistic picture has yet to be elucidated in depth in most venomous snake systems, however, recently this has been identified as a major goal in the field of venom evolution. Collectively, this dissertation represents an exploration of the major evolutionary drivers of venom variation in the CVOS clade of western rattlesnakes. Here, I outline that venom variation between species, subspecies, and populations is common throughout CVOS and that venoms can vary both in the presence or absence of specific toxins as well as in the abundance of specific toxin families. Phylogenetic history did not predict compositional trends at a broad geographic scale but did correlate with population-level venom variation in some cases. I also demonstrate that introgression between different species is a source of novel venom phenotypes with unusual properties. Abiotic factors, particularly temperature-related variables, may correlate with venom phenotype, however, the specific mechanisms for this relationship are unclear and should be further investigated. Finally, diet appears to be a more direct influence on venom compositional variation via the expression of either taxon-specific toxins or generalist toxins depending on prey availability. The broad trends explored here shed light on the complex and interconnected biotic and abiotic mechanisms responsible for venom variation in rattlesnakes.


272 pages

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