Exactly how sharks can sense the minute twitch of a faraway fish is a puzzle. But a team from the US has uncovered a big clue: a jelly-like substance produced by sharks, rays and skates turns out to conduct protons better than any other biological material measured.
The jelly fills specialised electrical sensory organs that form a network of deep pores dotted across a shark’s snout.
Stefano Lorenzini, an Italian physician and shark enthusiast, was the first to describe the enigmatic network of pores and canals in 1678.
The function of the ampullae of Lorenzini, as they became known, remained a mystery for nearly 300 years. It wasn’t until the 1960s that researchers recognised their role in detecting electric fields.
Many sharks are apex predators, with a knack for homing in on their prey. They do this by detecting the weak electric fields produced when a fish – or an unsuspecting surfer – contracts its muscles.
Sharks are extraordinarily sensitive to these fields, and a single pore-like ampulla is able to detect an electric field just 1.5 billionths of a volt in strength.
Sensory cells at the base of the pores transmit this information to the brain, but exactly how the ampullae of Lorenzini do this is unknown.
The new study, published in Science Advances, suggests that the conductivity of the jelly inside the pores could play a role.
Marco Rolandi from the University of California, Santa Cruz and colleagues squeezed jelly from the pimple-like pores of a bonnethead shark, and two species of skate.
They then measured the jelly’s ability to conduct protons, or charged hydrogen ions. A process of proton “hopping” relays the signal through the jelly.
The conductivity was higher than any other biological material tested to date, and only 40-fold lower than Nafion, a state-of-the-art proton-conducting polymer used in fuel cells.
Whether the jelly could have some applications in biosensors and biological transistors – an area the team specialises in – remains to be seen.
How proton hopping in the jelly triggers the ampullae sensory cells also needs to be investigated further.
“The ampullae of Lorenzini are such a fascinating organ,” says Rolandi.