Did you know that some squirrels have evolved to develop anti-venom proteins that protect them from rattlesnake bites? Did you know that some rattlesnakes have evolved specific venom chemistries depending on which squirrels are predominant in their area? Which are you more afraid of now – rattlesnakes or squirrels?
Evolutionary biologists at Ohio State University conducted a study of rattlesnakes and squirrels in Northern California in an attempt to figure out how squirrels there manage to survive rattlesnake bites. According to their report in Proceedings of the Royal Society B, they were surprised to also learn how rattlesnakes custom-blend their venoms like master brewers.
You could drive 20, 30 miles down the road and find a lot of variation in the venom and our research suggests that this variation is adapted to overcoming differences in squirrel venom resistance.
Study author and environmental ecologist Matthew Holding saw this variation when his team collected venom from northern Pacific rattlesnakes (Crotalus oreganus) and blood samples from California ground squirrels (Otospermophilus beecheyi) living in 12 different areas of northern California.
Then they played the favorite game of environmental ecologists: Venom versus Blood. The researchers mixed the samples from both the same and distant locations. After thirty minutes, they checked to see which had won.
While the rattlesnake venom was the overall winner, the samples showed that the rattlesnakes would have done best against squirrels in their immediate neighborhood and their success rate dropped quickly against squirrels from just a little farther away.
How did the real Snake Venom versus Squirrel Blood game evolve? Obviously, natural selection played a role on the squirrel side but it doesn’t explain how or why the snake venom got fined-tuned per squirrel population, says Holding.
It’s a complex and fascinating system with lots of other questions to ask.
Adding to the mystery is the fact that another study, also done by Ohio State scientists and published in the journal Toxicon, showed similar co-evolution in Ohio’s Eastern gray squirrels (Sciurus carolinensis). Those living in rattlesnake-free Columbus (home of The Ohio State University) did poorly (they died) against timber rattlesnakes (Crotalus horridus) in a park south of the city where other Eastern grey squirrels survived the bites.
What’s next? Stay tuned for Venom versus Blood II: Revenge of the Bushy Tails.