Analysis of natural snake venom inhibitors in snake blood began in the 18th century with the pioneering work of Fontana on European vipers (Hawgood, 1995). Serum resistance to conspecific and heterospecific venoms has subsequently been identified in many snakes, but results vary. Many of these snakes demonstrating resistance are either allopatric or distantly related, making the ecological explanation of this resistance unclear. Auto-resistance to one’s own venom for protection against self-envenomation has been suggested to be provided by endogenous serum-based protective molecules that bind to the venom components. Toxin resistance could develop in venomous organisms resulting from the physiological production of their own venom, but this connection remains unclear, and it is uncertain how broad or specific this protection is against other species with similar venoms. The United States has many species of pitvipers; these snakes are commonly social animals, often communally hibernating and providing maternal care to young, and they are not known to cannibalize other snakes. Due to these social behaviors, pitvipers are unlikely to cannibalize or even bite one another. Since New World pitvipers generally do not have any venomous predators, this removes any evolutionary selection pressures for resistance against predators, making this family a good model to test the relationship between toxin production and protection against those toxins. In general, pitviper venoms contain high levels of snake venom metalloproteases. Using microassays to measure metalloprotease activity in each venom from 42 individuals representing 3 genera and 17 species of pitvipers, and then measuring the effect of adding their serum to venom, inhibition of SVMP activity was measured. Individuals reduced average SVMP activity of all venoms by 44%. None of the results indicated that there was a higher efficacy towards one’s own individual, population, or species SVMPs, and the data showed high levels of inhibition variation between individuals of the same population and species. Additionally, results showed differential inhibition towards a snake’s venom phenotype. The presence of these broad spectrum SVMP inhibitors indicates that they may have evolved to defend against one’s own toxins but contain a wide range of efficacy to provide protection against future diversification of SVMP’s.
Hill, Kaleb, "AUTO-RESISTANCE TOWARD SNAKE VENOM METALLOPROTEASES IN UNITED STATES PITVIPERS" (2023). Master's Theses. 280.