Snake Venom - Evolution

Evolution

Snake venom consists of many different toxin proteins: these can either have enzymatic activity, which typically assists in digestion, or can be shorter peptides that are used to immobilize prey. Toxin proteins make up many multigene families, and arose from gene recruitment of proteins that do not code for toxins, followed by extensive evolutionary modification. Toxin evolution follows the birth-and-death model of gene families, where duplication followed by functional diversification results in the creation of structurally related proteins that have slightly different functions. It is thought that venom as a way to immobilize prey was beneficial in allowing the uncoupling of feeding system and locomotion, which are coupled in the Haenophidians, which then enabled snakes with venom systems to colonize open areas. Venom continue to evolve as specific toxins are modified to target a specific prey, and it is found that toxins vary according to diet in some species.

The presence of enzymes in snake venom was once believed to be an adaptation to assist digestion. However, studies of the western diamondback rattlesnake, a snake with highly proteolytic venom, show that venom has no impact on the time required for food to pass through the gut.