Sharks are archetypal predators, fine-tuned by over 400 million years of natural selection. Over this storied evolutionary history, these animals have picked up an arsenal of anatomical weapons that have helped them survive. But one of the least understood is a highly specialized sense organ known as the ampullae of Lorenzini, whose key element researchers have just discovered has the strongest proton conductivity of any biological material yet studied.
Named for the 17th century ichthyologist Stefano Lorenzini, who first described the adaptation in detail, the ampullae are pores in shark skin that open into subdermal jelly-filled canals connected to electrosensitive receptors. Incredibly, these organs allow sharks and other elasmobranchs—the evolutionary subclass that includes sharks, skates, and rays—to detect the weak electric fields surrounding their prey. Exactly how these hunters pull off this Electro-style superpower, however, has been under debate for centuries, which is what makes the new findings so exciting.
Now, a study published Friday in Science Advances suggests that the ampullae's success is linked to the extraordinary properties of its jelly. The authors identified the carbohydrate keratan sulfate as playing a key role in its unusually high conductivity, due to the compound's capacity to organize water into hydrogen bond chains that allow for optimal proton transfer.
"The observation of high proton conductivity in the jelly is very exciting," Marco Rolandi, an associate professor of electrical engineering at UC Santa Cruz and co-author on the study, said in a statement. "We hope that our findings may contribute to future studies of the electrosensing function of the ampullae of Lorenzini and of the organ overall, which is itself rather exceptional."
The discovery is not only a step towards a firmer understanding of the underlying dynamics of this unusual organ, but also has applications for material sciences. Synthetic substances with high proton conductivity, such as the polymer Nafion, are used in the development of more efficient fuel cells, so Rolandi and his colleagues think the biological counterpart in elasmobranch jelly could yield new insights into that effort. The unique electrosensory makeup of the ampullae of Lorenzini could also lead to the development of unconventional sensory technologies.