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.