Biochemical Ecology of Crotalus viridis (Prairie Rattlesnake) in Colorado

Smith, Cara F.

Mackessy, Stephen P.

School of Biological Sciences

University of Northern Colorado

Greeley, CO USA

Schield, Drew R.

Castoe, Todd A.

Department of Biology

University of Texas Arlington

Arlington, TX USA

Parker, Joshua M.

Biology Department

Fresno City College

Fresno, CA USA

Snake venoms are complex mixtures comprised primarily of potent bioactive proteins used for prey incapacitation. Venom composition has been shown to vary taxonomically, geographically, with age, and with dietary preference. North America’s most widely ranging rattlesnake, Crotalus viridis (Prairie Rattlesnake), is found from northern Mexico through the plains of the western United States to southern Canada. Coupled with its wide species range, C. viridis is also a habitat generalist and inhabits areas in close proximity to humans, increasing the likelihood of human encounters and bites from this snake. Crotalus viridis venom is known to induce hemorrhage and muscle degradation due to the presence of larger enzymes like snake venom metalloproteases (SVMPs) and snake venom serine proteases (SVSPs) and smaller nonenzymatic toxins targeting muscle (myotoxins). Though previous research on C. viridis has shown geographic variation in some venom toxins, to date, no analysis has done a deep investigation into variation in the entire venom proteome of this species. The current project investigates venom variation in the C. viridis throughout its range in Colorado by determining population-level patterns in abundance of major toxins and examining the relationship between venom phenotype and localized prey sources. SDS-PAGE, toxicity assays, high performance liquid chromatography, mass spectrometry and biochemical assays were used to characterize venom composition. The compositional patterns observed demonstrate an inverse relationship between highly enzymatic and nonenzymatic venom phenotypes, which broadly aligns with the typical type I-type II rattlesnake venom compositional dichotomy. In the future, we will examine the relationship between geographic variation in toxin abundances and differences in available prey species. Ultimately, the patterns of venom variation in C. viridis can help inform snakebite treatment in addition to providing clues about foraging ecology and venom evolution of this wide-ranging rattlesnake.

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