BIARDI, James E; Univ. of California, Davis and San Francisco State University: Ecological and Evolutionary Context of Mammalian Resistance to Snake Venoms

Snake venoms are a complex mixture of proteins, polypeptides, biogenic amines, and other components that may have neurotoxic, hemostatic, and/or hemorrhagic effects on prey. Their primary functions are to immobilize prey and initiate the process of digestion. For example, most viper venoms contain metalloproteases that break down the lining of blood vessels and other components of the extracellular matrix, leading to hemorrhage and tissue necrosis. However, some mammals are able to neutralize the toxins in of snake venoms. While clinical treatment of snakebite in humans relies on antibodies raised in domestic animals, resistance in prey appears to be an innate, not an immune, response to predation. The hemostatic and hemorrhagic effects of venoms pose a significant threat apart from death, since they can reduce fitness due to tissue destruction and necrosis. In some mammals, this threat has been met by the modification of endogenous serum protease inhibitors in ways that make them effective against snake venom proteases. This paper examines the current state of knowledge about mammalian factors that neutralize snake venom proteases and prevent extensive tissue damage. This work shows that five marsupials, two hedgehogs, a shrew, a mole, four mongoose, a raccoon, two mustelids, and 15 rodents (including three sciurid and eight murid rodents) have some form of resistance to venom toxins. An examination of new and existing data using an evolutionary and ecological perspective reveals previously unexplored patterns in venom resistance. There are significant gaps in our knowledge of innate defenses against venomous snakes, and a comparative approach can lead to new insights into the arms race between these predators and their prey.