Physiological Venom Resistance of Colorado Rodents to Desert Massasauga and Prairie Rattlesnake Veno

Balchan, Neil R.

neil.balchan@unco.edu

Mackessy, Stephen P. School of Biological Sciences

University of Northern Colorado

Greeley, Colorado, USA

The Red Queen hypothesis describes the coevolutionary dynamic between predator and prey where both partners must evolve in tandem to remain competitive. In several cases, rodents have demonstrated resistance to the venoms of their snake predators. For example, the California Ground Squirrel (Otospermophilus beecheyi) exhibits high resistance to the venom of the Pacific Rattlesnake (Crotalus oreganus). Conversely, cases exist where a prey species apparently lacks physiological resistance to the venom of its predator - the Cape Ground Squirrel (Xerus inauris) lacks venom resistance to the predatory Puff Adder (Bitis arietans) and Snouted Cobra (Naja annulifera). My research evaluates patterns of venom resistance in a Colorado grassland ecosystem, where the Desert Massasauga (Sistrurus tergeminus edwardsii) and Prairie Rattlesnake (Crotalus viridis) predate upon a suite of rodent species. Field sites are located in northern (one snake predator) and southern Colorado (two snake predators) to investigate patterns of resistance between and within locations at the geographic level. Median lethal dose assays are used to assess venom resistance of select rodent populations to specific rattlesnake venoms. Serum-based assays determine the protective effect that a rodent’s serum exhibits against specific venom components. Preliminary results indicate a moderate protective effect of the serum of Deer Mice (Peromyscus maniculatus) and Meadow Voles (Microtus pennsylvanicus) against Prairie Rattlesnake venoms, but not Desert Massasauga venom. Studying patterns of venom resistance in a system with two predators and multiple prey species allows us to understand better the evolution of such defenses and to evaluate whether local adaptation exists.