I think it’s important to clear the air before we dive in: I am terrified of snakes. Despite never being harmed or attacked by a snake, I have a shaking fear of these slithering reptiles (even a picture can raise my heart rate). In a somewhat unconventional twist, I am also fascinated by their diversity and ability to incapacitate much larger organisms with only a single bite. Why there is so much variation in venom, and what makes it so toxic?
What is snake venom?
As a form of reptilian saliva, snake venom is highly concentrated with a poisonous cocktail of active proteins and is produced and stored in a snake’s venom gland ready to be injected into unlucky predators or prey. (Lu, et al, 2005). Venom has evolved to affect the central elements of nearly every physiological pathway. According to Lu, “for almost every factor involved in coagulation or fibrinolysis there is a venom protein that can activate or inactivate it.” These processes of coagulation and fibrinolysis are critically important to the formation and regulation of blood clots. While neurotoxins are common components of the Hydrophidae and Elapidae species venom, we will focus on Viperidae venom which is generally comprised of hemostatically active components.
The coagulation abilities of some Viperidae species like the pit viper are enough to turn free flowing blood into a gooey solid similar to the strawberry jam pictured. How? The venom targets the blood’s ability to form clots through acting on specific blood coagulant factors, platelets, or tissues. The proteins in venom that affect coagulation factors are often classified as FV activators, FX activators, and thrombin-like enzymes (TLEs), which interfere at key steps in the body’s fibrinolytic pathway.
The high degree of variation in venom has interested researchers for decades. Understanding what causes this variation is critical to effectively treating snake bites, as the healthcare team should have the most accurate analysis of the venom. An article titled “Diet and snake venom evolution” seeks to account for this variation by examining three main hypotheses: variation is a function of geographical proximity, variation is associated with phylogenetic relationships, and variation is associated with geographical variation in diet.
An experiment was conducted by use of 67 snakes of the same species collected cross 36 localities in Vietnam, Thailand, and Malaysia. After collecting and analyzing samples of venom and feces, the data revealed the strongest correlation with venom and diet (0.5957). This demonstrates that the diet of a snake is an indicative variable in the evolution of its snake venom with its function relating closely to the size or characteristics of usual prey.
Daltry, J. C.; Wüster, W.; Thorpe, R. S. Letters to Nature 1996, 379 (6565), 537–540.
Lu Q, Clemetson JM, Clemetson KJ. Snake venoms and hemostasis. J Thromb Haemost 2005; 3: 1791–9.