Snake Venom Evolved Target the Right Prey.

• Position: REPTILES

Like wine, some snake venom is more complex than others. It all depends on the meal it is paired with. Research can tell us why, as a study in the journal Proceedings of the National Academy of Sciences shows that evolutionary diversity among prey--say, a combination of mice, turtles, and fish--has been the key driver of venom complexity in rattlesnakes, copperheads, and other North American pit vipers.

To arrive at this conclusion, researchers added data on the genes and proteins in venom samples to a century's worth of previous studies of what snakes ate. The team found that a diet consisting of prey with the greatest evolutionary distance between common ancestors was associated with snake venom that contained the widest range of toxins.

Snake venom incapacitates prey by disrupting a variety of physiological processes, attacking the nervous system, blood-clotting capabilities, cell membranes, and muscles. So, for example, a snake that eats mammals and amphibians would need venom that could act on the quite different constitutions found in each of those classes of animals.

"A mouse is a mouse is a mouse to a rattlesnake, whereas a mouse and a frog and a lizard are quite different because of the way that they're built, their physiology, and the way venom attacks them," explains study coauthor H. Lisle Gibbs, professor of evolution, ecology, and organismal biology at Ohio State University.

The finding suggests that species richness--the number of different species in an ecological community--is not the driving force behind predator trait complexity. Instead, snake venom complexity has evolved in response to the divergence, or how distantly related prey species are, to mirror the divergence of the venom's physiological...