April 20, 2010

How Do Cobras Raise Their Hoods?

Scientists measuring electrical activity in the muscles of a cobra have found the mechanism that triggers the frightening "hood flare" that the snake uses as a defensive display.

The scientists found a precise group of muscles that the cobra uses to raise their hoods. The procedure was very tricky. Scientists had to implant tiny electrodes into the snake's muscles while the reptile was carefully anaesthetized. Once the electrodes were in place, they took measurements of electrical activity from all of the muscles in the neck of the cobra.

Researchers explained that the cobra's hood evolved as its ribs were "co-opted" to be used as a visual display.

Kenneth Kardong, professor of zoology from Washington State University in the US, one of the authors of the study, explained that the cobra's hood was "an intriguing problem in evolutionary biology."

"In the cobra, both the [rib bones] and the muscles that work them are deployed to erect this visual display," Kardong explained to BBC News.

"We wanted to examine the way in which the ribs were 'freed up' to rotate into this presentation position, and to understand how the muscles were able to accomplish that and return them to a relaxed position."

"The riskiest part of the study," said Bruce Young, from the University of Massachusetts Lowell, was doing the surgery to implant the electrodes. "You have to work around the head but the snakes are prone to waking, which can be disconcerting," he explained.

Once the electrodes were connected, the team waited for the snake to recover before filming and recording the muscle activity as the cobra flared its neck. They found that eight muscles were involved in the process. An interesting note is that all the muscles the cobra uses to raise its hood, are also present in non-hooding snakes.

"This is an example of evolution's remodeling [as] derived species emerge," said Dr Kardong. "There's been a change in the nervous system's control over these muscles."

Professor Young explained that cobras were not the only snakes to hood. "Several groups of unrelated snakes show almost identical defensive behavior," he said. He said he would like to study those snakes to see how they raise their hoods as well.

The findings were reported in the Journal of Experimental Biology.


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