stylistic:tone, information:classification, structural:expansion, information:highlighting
Venom

Rattlesnake venom is hemotoxic, destroying tissue, causing necrosis and coagulopathy (disrupted blood clotting). In the U.S., the tiger rattlesnake (C. tigris) and some varieties of the Mojave rattlesnake (C. scutulatus) also have a presynaptic neurotoxic venom component known as Mojave type A toxin, which can cause severe paralysis. However, most North American rattlesnakes are not neurotoxic. Although it has a comparatively low venom yield, the venom toxicity of C. tigris is considered to be among the highest of all rattlesnake venoms, and among the highest of all snakes in the Western Hemisphere based on LD studies conducted on laboratory mice. C. scutulatus is also widely regarded as producing one of the most toxic snake venoms in the Americas, based on LD studies in laboratory mice.

Rattlesnake venom is a mixture of five to fifteen enzymes, various metal ions, biogenic amines, lipids, free amino acids, proteins, and polypeptides. More specifically, there are three main families of toxins in rattlesnakes: phospholipases A2 (PLA2s), snake venom metalloproteinases (SVMPs), and snake venom serine proteinases (SVSPs). It contains components meant to immobilize and disable the prey, as well as digestive enzymes, which break down tissue to prepare for later ingestion. The venom is very stable, and retains its toxicity for many years in storage.

Snake venom, in general, has a complex and ongoing evolutionary process, and rattlesnake venom is no different. The primary mechanisms of evolution are both gene duplication and gene loss events. The duplication events provided material for neofunctionalization to create the novel toxin genes, while gene loss influenced speciation and helped lead to such a wide variety of “chemical cocktails” in rattlesnake venoms. The prevailing theory for the driving force of this evolution is directional selection, where efficacy on prey is selected for. Diversity in prey leads to less specificity in toxins, while highly specialized toxins are more likely to develop when there are few key prey species. However, recently, balancing selection has been indicated to better explain the maintenance of adaptive genetic diversity in venom-related genes, potentially allowing for the rattlesnakes to better keep up in the evolutionary arms race with their prey.

Older snakes possess more potent venom, and larger snakes are frequently capable of storing larger volumes of it.