A thick and clear jelly produced by sharks, skates and rays is key to these predators to detect even the weakest electric fields produced by their prey and other animals, new research suggests.
The viscous jelly has the highest proton conductivity ever reported for any biological material, according to the study, published in the journal Science Advances. Proton conductivity refers to the ability of a material or solution to conduct an electric current made up of positive hydrogen ions.
The current flows swiftly through the jelly, which is produced by an array of unusual organs called the ampullae of Lorenzini.
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"The observation of high proton conductivity in the jelly is very exciting," Marco Rolandi, an associate professor of electrical engineering at the University of California at Santa Cruz Rolandi, said in a press release. "We hope that our findings may contribute to future studies of the electro-sensing function of the ampullae of Lorenzini and of the organ overall, which is itself rather exceptional."
He and his team analyzed the jelly and found that the substance's conductivity is only 40 times lower than the current state-of-the-art proton-conducting polymer, Nafion, which is widely used in fuel cell technologies. Nafion is in items like hybrid cars. It is chemically related to Teflon and looks like plastic food wrap, but is a lot thicker.
Sharks, skates and rays therefore, for probably millions of years, have been using a natural material that has nearly the same abilities as a product that humans only started to make and use in the late 1960s. (One of Nafion's first uses was in NASA's Gemini space program.)
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The discovery of the ampullae of Lorenzini goes back to 1678, when researcher Stefano Lorenzini first described the organs. They are visible as small pores in the skin around the head and on the underside of sharks, skates, and rays. Each pore is open to the environment and is connected to a set of electricity-sensing cells by a long canal filled with the jelly.
The integration of signals from several ampullae allows sharks, skates, and rays to detect changes in the electric field as small as 5 nanovolts (billionths of a volt) per less than half an inch. It has long been a matter of debate, however, as to how such weak signals are transmitted from each pore to the sensory cells.
While many questions still remain, Rolandi and his team suspect that a compound called keratan sulfate, also found in the ampullae of Lorenzini, provides the jelly with more protons for even higher conductivity.
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Human technological advances, such an innovations in electronic sensors, could be inspired by shark jelly in the future.