Shark Jelly Conducts Electricity
Sharks, skates and rays produce a gloppy jelly that has the highest proton conductivity ever reported for any biological material.
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.
"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.)
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.
Human technological advances, such an innovations in electronic sensors, could be inspired by shark jelly in the future.
ressing along the canals on the ventral side of an adult skate causes jelly to extrude from the pores of the ampullae of Lorenzini.
Controversy has surrounded the timetable of existence for megalodon, the world's largest ever shark, but a new study concludes that this 60-foot-long predator became extinct 2.6 million years ago. The study, published in the latest issue of the journal PLOS ONE, counters other theories that megalodon (
) became extinct much later, with some even believing that the enormous shark never did die out. "I was drawn to the study of
extinction because it is fundamental to know when species became extinct to then begin to understand the causes and consequences of such an event," explained lead author Catalina Pimiento.
If megalodon did indeed become extinct 2.6 million years ago, then members of our genus
were not around when the huge shark was still alive. Human-like beings were in existence, however, such as members of the genus
, shown here. Many other terrestrial animals also existed, as did birds, plants and insects.
While not as large as monstrous megalodon, other big sharks lived at the same time. Dana Ehret, curator of paleontology for the Alabama Museum of Natural History, told Discovery News that
"most likely shared habitat" with megalodon. It belonged to the same genus as today's great white sharks and was just as fierce.
Non-avian dinosaurs were long gone by the time megalodon emerged, as they all died out 66.5 million years ago. Many of their bird relatives, however, were going strong during megalodon's lifetime. Some, including
— aka Terror Bird — were formidable in their own habitats. Terror Bird is thought to have stood 8-feet-tall and weighed over 300 pounds.
Ehret and other paleontologists believe that megalodon frequently feasted on whales. One such species was
, shown here. Megalodon is thought to have emerged approximately 17 million years ago, while Squalodon went extinct around 14 million years ago. Was the whale's entire population eaten to death over time? That has not been ruled out, although researchers have also proposed competition from dolphins and climate change as other possible reasons for the whale's extinction.
Evidence suggests that seals have been on Earth for at least 15 million years. Ehret said that they would have been in megalodon's habitat. Seals likely served as meaty snacks for megalodon.
Leatherback sea turtles are the only living species in the genus
. Many other members of this genus existed in years past, however, including giant sea turtles during megalodon's time. Could megalodon have bitten through their hard shells? The answer is probably not, based on modern great white shark bite force measurements and behavior. Megalodon's teeth were nonetheless formidable. Ehret said that the teeth were "much different" than those of other sharks during megalodon's lifetime, "having much finer serrations, being much thicker, and possessing a 'chevron,’ which is a V-shaped portion of the tooth crown."
Large, plant-loving Desmostylus was a hippo-like animal that lived during the earlier part of megalodon's time on the planet. Comfortable both on land and in water, Desmostylus surely would have attempted a hasty getaway if megalodon were near. Desmostylus usually ventured in freshwater, though, seeking aquatic plants.
The first penguins are thought to have emerged around the time of the mass extinction event 66.5 million years ago that ended the Cretaceous Period. Ehret said penguins would have shared habitat with megalodon. Some prehistoric penguins grew to be quite large, such as "Colossus," which stood 6'7" tall. It preceded megalodon's existence, however. The penguins during the large shark's lifetime would have been like a kernel of popcorn to megalodon, which probably exerted more effort targeting much larger prey.
When one animal goes extinct, the void can really benefit other species. Dinosaur extinction, for example, benefitted mammals, which evolved to become the world's dominant animals. Pimiento similarly believes that megalodon's demise led to bigger whales. "When we calculated the time of megalodon's extinction, we noticed that the modern function and gigantic sizes of filter feeder whales became established around that time," Pimiento said. "Future research will investigate if megalodon's extinction played a part in the evolution of these new classes of whales."