Squamata - Evolution of Venom

Evolution of Venom

Recent research suggests the evolutionary origin of venom may exist deep in the squamate phylogeny, with 60% of squamates placed in this hypothetical group called Toxicofera. Venom has been known in the families Caenophidia, Anguimorpha, and Iguania, and has been shown to have evolved a single time along these lineages before the three families diverged, because all lineages share nine common toxins. The fossil record shows the divergence between anguimorphs, iguanians, and advanced snakes dates back roughly 200 Mya to the Late Triassic/Early Jurassic.

Snake venom has been shown to have evolved via a process by which a gene encoding for a normal body protein, typically one involved in key regulatory processes or bioactivity, is duplicated, and the copy is selectively expressed in the venom gland. Previous literature hypothesized venoms were modifications of salivary or pancreatic proteins, but different toxins have been found to have been recruited from numerous different protein bodies and are as diverse as their functions. lort

Natural selection has driven the origination and diversification of the toxins to counter the defenses of their prey. Once toxins have been recruited into the venom proteome, they form large, multigene families and evolve via the birth-and-death model of protein evolution, which leads to a diversification of toxins that allows the sit-and-wait predators the ability to attack a wide range of prey. The rapid evolution and diversification is thought to be the result of a prey/predator arms race, where both are adapting to counter the other.