Meeting Abstract
Many animals use toxic chemicals to defend themselves or immobilize prey. The use of such compounds frequently leads to antagonistic coevolution, wherein impacted species evolve physiological resistance to the effects of these toxins and create reciprocal selection for increasingly novel toxins or delivery systems. For example, many pitviper venoms contain high levels of metalloproteinases, a class of toxins that cause hemorrhaging, tissue damage, and facilitate the spread of other toxins through the tissues of injected prey. Several different lineages of mammals (including sciurid and neotomine rodents) have evolved metalloproteinase inhibitors, proteins in the blood serum which neutralize metalloproteinases and impede the effectiveness of the venom. Individuals with high levels of inhibitors can survive envenomations that would rapidly immobilize or kill non-resistant mammals. However, there are apparently evolutionary and physiological factors that constrain snake venom resistance, because individuals of resistant species of ground squirrels and woodrats are still the primary prey items of local rattlesnakes. Venom resistance and venom chemistry can vary at the level of species, populations, and individuals. We are studying the venom of two rattlesnakes (Crotalus oreganus and C. ruber), and resistance of two mammals (Otospermophilus beecheyi and Neotoma lepida) which all co-occur at four different locations. We use fluorescent gelatinase assays to quantify metalloproteinase efficacy and resistance among individuals. We have paired venom and serum samples within and between populations to assess variation in these traits at multiple biological levels of organization.
