Patterns and drivers of venom variation in the Western Rattlesnake (Crotalus viridis viridis)


Smith, Cara

smithcf385@gmail.com


Department of Biochemistry & Molecular Genetics

University of Colorado School of Medicine

Aurora, Colorado USA


Nikolakis, Zachary L.

Ivey, Kathleen

Perry, Blair W.

Castoe, Todd A.

Department of Biology

University of Texas at Arlington

Arlington, Texas USA


Saviola, Anthony J.

Hansen, Kirk C.

Department of Biochemistry & Molecular Genetics

University of Colorado School of Medicine

Aurora, Colorado USA


Schield, Drew R.

Department of Ecology & Evolutionary Biology

University of Colorado

Boulder, Colorado USA


Balchan, Neil

Mackessy, Stephen P.

School of Biological Sciences

University of Northern Colorado

Greeley, Colorado USA


Parker, Joshua

Fresno City College

Fresno, California USA


Snake venoms are trophic adaptations that represent an ideal model to examine the evolutionary factors that shape polymorphic traits under strong natural selection. Venom compositional variation is substantial within and among venomous snake species. However, the forces shaping this phenotypic complexity, as well as the potential integrated roles of biotic and abiotic factors, have received little attention. Here, we investigate geographic variation in venom composition in a wide-ranging rattlesnake (Crotalus viridis viridis) and contextualize this variation by investigating dietary, phylogenetic, and environmental variables that covary with venom. Using shotgun proteomics, venom profiling, and lethality assays, we identify 2 distinct divergent phenotypes that characterize major axes of venom variation in this species: a myotoxin-rich phenotype and an SVMP-rich phenotype. We find that while phylogenetic relationships do not explain the geographic distribution of venom variation, dietary availability, and temperature-related abiotic factors are correlated with geographic trends in venom composition. Our findings highlight the potential for snake venoms to vary extensively within species, for this variation to be driven by biotic and abiotic factors, and for the importance of integrating biotic and abiotic variation for understanding complex trait evolution.