Raptors without resistance: No evidence for endogenous inhibition of rattlesnake venom metalloproteinases in a Great Plains raptor assemblage

Abstract

Snake venoms are complex biochemical secretions under strong selection for prey subjugation, and venoms are tightly linked to the biotic communities that snakes inhabit. Physiological adaptations for venom resistance have been identified in various snake prey species, but fewer snake predators, with research in this area largely biased towards mammalian species. Fewer investigations have assayed for the presence of resistance mechanisms in avian systems. Birds of prey (hereafter “raptors”; orders Accipitriformes, Falconiformes, and Strigiformes) represent major sources of predation for snakes. Raptor dietary habits range from snake specialists to non-snake feeders, and this continuum of snake predation frequency among species creates the ideal system in which to explore the presence and strength of venom resistance. We assayed sera from a suite of Great Plains raptors against snake venom metalloproteinases (SVMPs) of the Prairie rattlesnake (Crotalus v. viridis) to test the general hypotheses that 1) raptor sera will display elevated SVMP inhibition compared to a naïve avian model (domestic chicken; Gallus gallus) and 2) raptor species with high levels of rattlesnake predation will more effectively inhibit SVMP activity than those that are not known to feed on rattlesnakes. We found that raptors do possess elevated SVMP inhibition in comparison to a naïve avian model, but this level of inhibition remains low and is unlikely to be biologically significant in detoxifying venoms. We found no evidence suggesting that inhibitory potential of different raptor sera corresponds to the level of rattlesnake predation associated with each species. The widespread lack of SVMP inhibition in diverse raptors underscores the complexity of venom resistance dynamics in natural systems and further suggests that physiological venom resistance mechanisms may be poorly developed in birds more broadly.