A recent study explored how shark’s electrosensing organ reacts when it detects tiny electrical fields emanating from nearby prey.
The study, funded by the National Institutes of Health and published in the journal “Nature,” was conducted by David Julius, Ph.D., professor and chair of physiology at the University of California, San Francisco, and post-docs Nicholas W. Bellono, Ph.D. and Duncan B. Leitch.
“Sharks have this incredible ability to pick up nanoscopic currents while swimming through a blizzard of electric noise. Our results suggest that a shark’s electrosensing organ is tuned to react to any of these changes in a sudden, all-or-none manner, as if to say, ‘attack now,’” Julius said via press release.
Researchers showed that the shark’s responses may be very different from the way the same organ reacts in skates, the flat, winged, evolutionary cousins of sharks and sting rays, and this may help explain why sharks appear to use electric fields strictly to locate prey while skates use them to find food, friends, and mates. They also showed how genes that encode for proteins called ion channels may control the shark’s unique “sixth sense.”
“Ion channels essentially make the nervous system tick. They play a major role in controlling how information flows through a nervous system. Mutations in ion channels can be devastating and have been linked to a variety of disorders, including cystic fibrosis and some forms of epilepsy, migraines, paralysis, blindness and deafness,” said Nina Schor, M.D., Ph.D., deputy director at NIH’s National Institute of Neurological Disorders and Stroke. “Studies like this highlight the role a single ion channel can play in any nervous system, shark, skate, or human.”
In both sea creatures, networks of organs, called ampullae of Lorenzini, constantly survey the electric fields they swim through. Electricity enters the organs through pores that surround the animals’ mouths and form intricate patterns on the bottom of their snouts. Once inside, it is carried via a special gel through a grapevine of canals, ending in bunches of spherical cells that can sense the fields, called electroreceptors. Finally, the cells relay this information onto the nervous system by releasing packets of chemical messengers, called neurotransmitters, into communication points, or synapses, made with neighboring neurons.
Further experiments suggested that these contrasting responses may be due to different ion channels genes, which encode proteins that form tunnels in a cell’s membrane, or skin. When activated the tunnels open and create electrical currents by allowing ions, or charged molecules, to flow in and out of the cell.
Almost every field raised their breathing rates to a level seen when they smelled food, suggesting their system is tuned for one thing: catching prey.
“In short, it’s cool!” said Dr. Julius. “We’re on a mission to understand how the nervous system controls pain and other sensations. Sharks and skates have a unique sensory system that detects electrical fields. Although humans do not share this experience, you can learn a lot from studying unique, or extreme, systems in nature. It’s also a captivating way to learn about how evolution shapes the senses.”