Snake venom evolved to kill specific squirrels
with shocking precision
Kaplan, Sarah . Weblog post. Washington Post – Blogs , Washington: WP Company LLC d/b/a The
Washington Post. May 20, 2016.
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In high school biology, you learned that co-evolution was an arms race. Gazelles speed up to escape cheetahs,
who grow ever-swifter as the generations pass. Crabs grow more powerful claws to puncture snails’ thicker and
thicker shells. Every living thing on Earth is engaged in a battle to become bigger, safer, deadlier, smarter, faster,
harder to track and more difficult to evade.
But evolution is not always an all-out war. Sometimes it’s more subtle — an ever-evolving negotiation between two
species that are constantly sizing up one another, seeking out vulnerabilities and adjusting their strategies in
response to what they find. It’s diplomatic. Except instead of concluding with peace, these negotiations end when
one animal eats the other. (Let’s not share this metaphor with anyone at the United Nations.)
Take, for example, the rattlesnakes and squirrels of northern California, combatants in a notoriously bitter conflict
that has raged over centuries. Each species is armed to the teeth (literally). Squirrels team up to mob their
rattlesnake predators, ward them off with bushy tails, and even chew up snake skin and rub it on their fur to
confuse snakes trying to sniff them out (which is so meta). Snakes, meanwhile, perfect stealthy slithers and
possess heat-sensing pits on their faces, not to mention incredibly toxic venom.
But, as is fitting for a savvy snake, a rattler uses its chief weapon as a scalpel, not a sledgehammer. A study
published this week in the journal Proceedings of the Royal Society B found that California rattlesnakes’ venom is
carefully calibrated to overcome the specific defenses raised by the squirrels in their region. As a result, the venom
varies measurably from county to county, possibly even from one highway exit to the next. California snake venom
is kind of like wine — it comes in regional varieties. None of which you want to be drinking.
The battle starts at birth, when squirrels begin creating anti-venom proteins that they pump into their blood stream,
arming themselves for the day when a rattlesnake attacks. These proteins vary based on the environment —
altitude, annual rainfall, type of vegetation — and on the venom of the snakes that live in the region.
[These bugs have a startling strategy for keeping predators away]
In response, the snakes are constantly tweaking the composition of their own venom, working on ways to
overcome those defenses.
“It’s like a lock and a key,” said Matthew Holding, an evolutionary ecologist at Ohio State University and the lead
author of the study. “Resistance is a lock and venom is the key and I have to have the right key to open the door.”
This process isn’t a conscious one; it’s a product of natural selection. Squirrels with inadequate defenses get eaten
before they can pass their wimpy genes down to their children. Likewise, snakes with unsuitable venom starve to
death before they can reproduce. Those that do live are the ones best suited for battle.
And at the moment, the snakes seem to have the upper hand, Holding said. When he and his colleagues tested 12
venoms from 12 different regions against 12 squirrel blood samples from those same areas, the venoms usually
beat out the blood from their same region. These fights were staged in test tubes, but it’s simple to imagine what
they mean for the real world: lots of dead squirrels.
[Fine feathers: Why red birds look so fit and sexy]
That’s surprising, Holding said, because most theories of evolutionary biology predict that prey’s defenses should
be marginally better than their predator’s weapons. Prey, after all, have more to lose.
“It’s a longstanding idea called the Life-Dinner principle,” Holding said. “If the predator loses in a given contest it
just misses a meal. But if the prey loses it dies.”
Natural selection should work more intensely on those that avoid dying than ones who simply manage to get
dinner, he continued. But the snake venom study suggests that something more complex may go down when two
It’s important that we understand how this works — and not just because it’s interesting to evolutionary biologists
(or because we feel bad for squirrels). Venomous snakes bite several thousand people a year in the United States,
and every year a few of those people die. Doctors, pharmaceutical companies and ophidiophobes would all like to
know more about variation in snake venom and ways of protecting against it.
“It’s a complex and fascinating system with lots of other questions to ask,” Holding said.
How did the giraffe get its improbable neck? Genetic analysis finds some clues.
Lady spiders demand gifts from their gentleman callers — or else they eat them
Listening for love: How female crickets got so good at hearing their mates
Scientists pinpoint the genes that give Darwin’s finches their distinct beaks
Publication title: Washington Post – Blogs; Washington
Publication year: 2016
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Publication date: May 20, 2016
Section: Speaking Of Science
Publisher: WP Company LLC d/b/a The Washington Post
Place of publication: Washington
Country of publication: United States, Washington
Publication subject: General Interest Periodicals–United States
Source type: Blogs, Podcasts, &Websites
Language of publication: English
Document type: Blogs
ProQuest document ID: 1790144987
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Copyright: Copyright WP Company LLC d/b/a The Washington Post May 20, 2016
Last updated: 2018-10-08
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Snake venom evolved to kill specific squirrels with shocking precision
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