miércoles, 8 de junio de 2016

Electric Eels Found To Leap Out Of Water To Shock Predators

Main image credit: Josh More/Flickr CC BY-NC-ND 2.0
ELECTRIC EELS HAVE BEEN FOUND TO SHOW SHOCKING LEAPING BEHAVIOR.
As if growing up to 2 meters and being able to produce an electric shock equivalent to that of a Taser isn’t impressive enough, researchers have confirmed a more unusual aspect about the electric eel. It seems that the animal, which isn’t actually an eel but a type of knife fish, isn’t content with just shocking its attackers underwater, but that under the right conditions they will leap out of the water to stun predators. 

More than 200 years ago, when the famous Prussian naturalist and geographer Alexander von Humboldt made the first scientific exploration to describe Latin America he faced many difficulties. But one of his most famous encounters occurred on March 19, 1800, when he described how locals caught electric eels by driving horses into the river, where the fish would then leap out of the water and stun the poor animals. This dramatic description quickly entered into legend, but in the centuries that followed no one had seen this unusual behavior repeated, leading most to think that von Humboldt exaggerated his electric experiences with the eels.

Yet it seems that there is far more truth to these accounts than anyone had previously given credit for. “The first time I read von Humboldt's tale, I thought it was completely bizarre,explains Kenneth Catania, who has described this behavior for the first time in the Proceedings of the National Academy of Sciences. “Why would the eels attack the horses instead of swimming away?” 
The eel jumps up to place its chin on the "predator" before shocking it. Kenneth Catania/Vanderbilt University
He actually corroborated these original accounts in the first place by accident. Studying the eels at Vanderbilt University, he was attempting to catch them from their tank using a metal rimmed net (“In hindsight, probably wasn't the best design to use,” he notes). He found that every so often, the eels would leap from the water and press their chins against the net, while at the same time generating a series of high-voltage pulses.

By measuring the power of the shocks used during this electric behavior, Catania was able to determine that the eels used a different shocking pattern than they used to stun prey. He found that they only leap from the water to attack living animals that are partially submerged, and did so with more frequency when the water level in their tank was lowered. This, suggests Catania, implies that the behavior is used to protect themselves against land-based predators when the eels feel cornered or threatened, such as in the dry season when the water levels are much lower. This is also the time when some of the eels breed.


But why leap from the water, rather than just sidling up close? Well, it seems that the higher up the intruder they can get, the more powerful the shock they deliver. When shocking in the water, the electric current dissipates through the water, but by hitting the target with its chin and then shocking, the current travels through the target's body. “This allow the eels to deliver shocks with a maximum amount of power to partially-submerged land animals that invade their territory… [while] also allow[ing] them to electrify a much larger portion of the invader's body,says Catania.

So after over two centuries of doubt and despite great interest in the animals, it seems that von Humboldt has finally been proven to be right, and that electric eels really do jump from the water to attack predators.

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