Deadly Coral Snake Venom Variety Has Unexpected Evolutionary Pattern

Snake venom comes in all varieties, as different as the snakes that use it. Now, scientists have taken a closer look at these differences and have discovered an unexpected evolutionary pattern among venomous snakes.

Each venomous snake species produces a unique venom, a mixture of about 50 to 200 toxic proteins and protein fragments that co-evolve with the typical prey of the snake, such as the smaller reptiles eaten by the eastern coral snake or the rodents preferred by rattlesnakes. During the course of evolution, any genetic variants that enhance venom resistance tend to spread through the prey population and, in turn, prompt tweaks to the snake venom.

In theory, there should be local co-adaptations between predator and prey in addition to considerable regional diversity in the types and amounts of different venom proteins. Yet when the researchers collected and profiled venom from eastern coral snakes at many sites within Florida, they found no variation at all.

"We were shocked," said Darin Rokyta, one of the researchers, in a news release. "This is the first time anyone has looked at venom variation at this scale, and everybody has assumed that the co-evolutionary arms race would case local populations to diverge quickly."

There could be several explanations for the lack of variation in these coral snakes. For example, a small population of the species might have recently expanded and taken over the entire range, displacing other populations and reducing genetic diversity. It could also be due to a difference in co-evolutionary dynamics between the species and its typically reptilian prey.

Currently, the researchers plan to use genetic clues to the population histories of each species to investigate possible explanation. The results could be helpful to researchers when it comes to developing coral snake antivenom.

"The received wisdom was that venoms are rapidly-evolving, but now we know that's not necessarily the case," said Mark Johnston, one of the researchers. "Clearly, venom evolution in these two snake species has been shaped by different forces. The next challenge is to understand why."

The findings are published in the journal Genetics.

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