March 15, 2010

Experiments Show How Snakes See At Night

Scientists reported on Sunday that some snakes can detect the faint body heat from prey three feet away with enough precision and speed to hunt in the dark.

Scientists have known for decades that rattlesnakes, boas and pythons have pit organs between their eye and nostril to sense infrared radiation in their environment.

The western diamondback rattlesnake is in a league of its own by having the ability to heat-seek up to 10 times more precisely than any of its relatives.

The snake has shown the ability to track and kill prey blindfolded.

However, it has remained a mystery to scientists how these reptiles have the ability to detect and convert infrared signals into nerve impulses.

One theory is the photochemical process beneath the snake's vision, where the eye sees electromagnetic radiation in the form of photons that activate receptor cells, which converts the energy into a biochemical signal to the brain.

Some fish are able to see infrared wavelengths of the electromagnetic spectrum.

However, molecular biologist David Julius of the University of California in San Francisco demonstrated in laboratory experiments that a different neurological pathway was at work for the serpentine "sixth sense."

"In this case, the infrared radiation is actually detected inside the pit organ as heat," Julius said in a phone interview with the AFP news agency. "We found the molecule responsible."

He said that a very thin membrane inside the pit organ warms up as the radiation enters through an opening of the skin.

The membrane is very sensitive to changes in temperature because it is in a hollow space.

"The heated tissue then imparts a signal to nerve fibers to activate the receptors we have identified," known as TRPA1 channels.

The neurochemical pathway suggests that snakes can feel heat rather than see it.

"The molecule we found belongs to a family of receptors related to pain pathways in mammals," Julius said.

The equivalent to this mechanism in humans is called the "wasabi receptor," which allows our sensory nervous system to detect irritants.

However, it is not activated by heat.

Julius' discovery, which was published in Nature, may help show how snakes evolve. 

"Studying change in sensory molecules is an interesting way to look at evolution because as animals inhabit different niches, smell and taste different things, hunt different animals, their sensory systems have to adapt," Julius said.

His discovery also suggests that the forces of natural selection yielded the same remarkable heat-seeking mechanism in reptiles on separate occasions.

"It is amazing to think that random mutation could have come up with the same kind of solution more than once," Julius said.


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