Home Advantage Gives Rattlesnake Venom an Edge

May 23, 2016 | Erica Tennenhouse

rattlesnake vs squirrel
Photo credit: Snakes: Dawn Endico/flickr (CC by SA 2.0). Squirrels: Benefactor123/Wikipedia (CC BY 3.0)

Snakes vs. Squirrels

Throughout California, Northern Pacific rattlesnakes wage an ongoing battle against California ground squirrels. It might seem like an unfair match, as the rattlesnakes have toxic venom at their disposal. But the squirrels have risen to the challenge, developing effective immune defenses over evolutionary time.

In a new study published in the journal Proceedings of the Royal Society B, researchers collected venom and blood samples from rattlesnakes and ground squirrels living in 12 spots in California to examine how location might affect the outcome of the battle between snake and squirrel.

Venom was placed in petri dishes with blood serum of squirrels from either the snake’s home turf or one of the other locations.

After a 30-minute match between rattlesnake venom and squirrel serum played out, the researchers measured how active the venom remained compared to how strong it had been before it encountered the serum. Less venom activity at the end meant there was a better chance the squirrel would have survived the attack.

The researchers found that rattlers battling their squirrel neighbors had a huge advantage in most locations, whereas their venom was less effective when pitted against the serum of non-local squirrels.

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Matthew Holding, a graduate student at Ohio State University and lead author of the study, said in a press release, “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."

Though the squirrel serum also showed traits that were adapted to the local snakes, it remains unclear to Holding why the rattlesnakes appear to have the home advantage. But at any given point in an evolutionary arms race, one species is bound to find itself in the lead.

The vast geographical variation in venom function identified in the study indicates that the snakes do not produce a universally potent venom that works equally well on all squirrels.

Insights gained from this research could help manufacturers of anti-venoms tweak their recipes to make products that are effective against a wide spectrum of venoms, according to Holding.

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