SAN FRANCISCO — We often point to a shark’s razor-sharp teeth, incomparable strength, and elite speed when it comes to their extraordinary ability to hunt, but a new study finds they use a super-sensitive electrical “sixth sense” that, no matter how faint, signals them to pinpoint and attack.
Sharks are one of the most fearsome predators on the planet. Their bodies and their senses — from smell to sight to touch — are all tuned for one thing: finding and killing prey. This latest research, funded by the National Institutes of Health, was aimed at finding the links between evolution and the senses in animals. Instead it wound up revealing how sharks possess an unparalleled sensor of sorts that allows them to pick up on the tiniest of electrical fields from living things in nearby waters.
“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,'” explains Dr. David Julius, professor and chair of physiology at the University of California, San Francisco and senior author of the study, in a release.
For the study, the authors exposed chain catsharks along with skates, a close cousin to sharks, to various levels of low voltage frequencies, and then measured their breathing rates. While skates’ breathing rates tended to vary from little reaction to significant movement, the research team found that sharks’ breathing rates increased to practically the same level every time, which supported the notion that the fish are constantly seeking out prey.
“In almost every way, the shark electrosensory system looks like the skate’s and so we expected the shark cells to respond in a graded manner,” says co-author Dr. Nicholas W. Bellono. “We were very surprised when we found that the shark system reacts completely differently to stimuli.”
The research team determined that though they both possess the same “electrosensing organ,” the two species use their abilities differently. Skates use their ectrosense organ to find mates, food, and friends while sharks, of course, use theirs to hunt. Sharks, on the other hand, simply used theirs to find prey.
These reactions from sharks are believed to be activated by genes that encode proteins, known as “ion channels,” which other animals also possess.
“Ion channels essentially make the nervous system tick. They play a major role in controlling how information flows through a nervous system,” says Dr. Nina Schor, deputy director at the NIH’s National Institute of Neurological Disorders and Stroke. “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.”
Which is what makes these latest findings all the more valuable for researchers.
“Studies like this highlight the role a single ion channel can play in any nervous system, shark, skate, or human,” says Schor.
Adds Julius: “In short, it’s cool! 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.”
The full study was published May 30, 2018 in the journal Nature.
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