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Robosquirrel’ Helps Tell An Epic Story Of Evolution

Evening Edition

In California, the ground squirrel is natural prey for the rattlesnake. So I’m a little perplexed when biologist Rulon Clark shows me a video, in which a squirrel approaches a rattler so it can get face to face with it.

"This is the typical display,” he said. “They'll approach, get really close and do this tail flag while they inspect the snake."

The most enduring relationship in nature is between predator and prey. Clark is part of a team that's discovered how evolution has changed relations between this pair of antagonists -- rattlesnakes and ground squirrels. And he’s done it with a little help from a robot.

Aired 7/3/12 on KPBS News.

A San Diego State University biologist shows how evolution has changed the rattlesnake and its prey, the ground squirrel, and he does it with a little help from a robot.

Rulon Clark is a snake guy. He’s a professor of biology at San Diego State University, and this summer he's in northern California studying the way rattlesnakes and ground squirrels play the game of survival. Clark becomes excited talking about rattlesnake-squirrel relations, an evolutionary story he calls “epic.”

But before we get to that epic, let's learn why squirrels wave their tails at snakes.

When the ground squirrel approaches the snake, it holds its tail erect and flags it from side to side as if the squirrel were an old-time navy signalman.

Clark said the rattlesnake, meanwhile, is like a gun with one bullet. When it strikes, it gives itself away and loses its coiled launching pad. If it misses the prey, the prey gets away.

"It all has to do with the snake relying on (stealth) and ambush,” he said. “If the animals around that area are on the lookout for snakes, the odds of a snake being successful – very low."

So the squirrel flags its tail, even raising the temperature of its tail to send infrared signals to the rattlesnake.

"So the tail flag seems to be a way to say to the snake, 'I'm ready to jump away.' Sometimes the squirrel doesn't even know the snake is there for sure, but it's still tail flagging," said Clark.

This body language seems to make the snake withhold its strike. But how do you create a reliable way to test this theory? Meet robosquirrel.

A tail-flagging robosquirrel from the perspective of the snake.
Enlarge this image

Above: A tail-flagging robosquirrel from the perspective of the snake.

The creation of UC Davis engineer Sanjay Joshi, robosquirrel is a taxidermied squirrel with a mechanical tail that mimics the tail flagging movement.

In another video, we see it placed, face-to-face, with a rattlesnake. When robosquirrel flags his tail, the snake does not strike. But when the tail remains still, the snake strikes, to its great disappointment. Just another robosquirrel.

Now let's get back to that epic story, Rulon Clark was talking about. The story is evolution. Or, to be specific, coevolution.

"Coevolution is evolution but it's between two parties that are continually adapting to each other,” said Clark.

He points out you can have “mutualistic” coevolution between plants and their pollinators, in which the two parties benefit each other.

“Then you can have ‘antagonistic’ coevolution, also a very powerful force,” he added. “Two parties that are at odds like host-parasite or pathogen-human."

Or ground squirrel-rattlesnake, fighting the battle of predation over thousands of generations, making each other genetically stronger and more cunning.

Rulon Clark's research is pure scientific research, but it could have practical applications. Co-evolution has made ground squirrels quite resistant to snake venom. Clark said studying the squirrel's genetics might, some day, lead to snake-bite treatments for humans.

Video by Nicholas McVicker

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