We all know that sight, sound, taste, touch, and smell are the five human senses, but really they’re just the beginning.
There are things like proprioception, the sense of orienting your body in space, and other senses even have subtypes. Within touch, for instance, mechanoreception detects surface texture, while thermoreception discerns temperature. There are also different types of vision that pick up infrared or ultraviolet light. And for some animals outside the genus Homo, they even possess electroreception — the ability to perceive electric fields.
This natural superpower clues creatures into the ubiquitous electrical signals that all living things — and some non-living things — emit. It’s as much of an ambient quality as the sounds of a cafe’s gentle chatter or the sumptuous aromas of its caffeinated creations. (Though, we don’t experience it, so we can’t know for sure.)
The newest animal discovered to have electroreception is the bottlenose dolphin (Tursiops). Already known for being one of the smartest animals on the planet, these golden retrievers of the sea can indeed perceive the weak electric fields surrounding them, and researchers demonstrated this remarkable ability in a study published today in the Journal of Experimental Biology. This finding further enriches our understanding of these brainy porpoises that use electroreception for both hunting and migrating.
Dolphins Go Electric
All living creatures emit electric fields — after all, the neural activity in our bodies is just electricity — and detecting these fields in the water is especially vital as this aquatic medium is better than air for transmitting electrical impulses, even extremely weak ones.
To sense those unseen electric fields, bottlenose dolphins use dimples called vibrissal pits on their beak. These pits hold whiskers when a dolphin is born, but fall out soon after. Researchers once believed these dimples were simply vestigial structures, but a study on a single Guiana dolphin (Sotalia guianensis) confirmed that they can detect electric fields and are crucial for locating other animals.
The follicles fill with seawater and contain receptors that respond to electric stimulus and register it in the brain, senior author Guido Dehnhardt, a marine biologist at the University of Rostock’s Marine Science Center, tells Inverse. Although scientists still don’t know the biological mechanism behind these receptors, this sense, or “modality,” as the authors call it, helps paint a bigger picture. Biologists can now contextualize some behavior as responses to the weak electric field dolphins feel pulsing around them. For example, when bottlenose dolphins stir up sediment while hunting for fish, they could be tracking their prey by following their electric fields, which leaves a trace in the sand.
To test this newly discovered ability, trainers at the Nuremberg Zoo taught two dolphins to first rest their jaws on a metal bar in their tanks and then placed electrodes right above their snouts. The dolphins, named Dolly and Donna, learned to swim away less than five seconds after feeling an electric field pulsed through these electrodes, signaling their response to the stimuli. The team started with an electric field at 200 microvolts per centimeter, going all the way down to 2 microvolts per centimeter. Both dolphins sensed the strongest fields, but Donna was evidently more sensitive to fields as low as 2.4 microvolts per centimeter, while Dolly’s threshold was 5.5 microvolts.
The team then upped the stakes by changing the electric fields from constant static to a pulse, which mimics what sea creatures produce. They pulsed electric fields 25, five, and finally one time per second as they reduced strength. Regardless of the pulse rate, Donna and Dolly could still pick up on these oscillating fields at varying voltages.
Sensing Electrons
So what does sensing electricity feel like? Dehnhardt compares the feeling to a very light pricking sensation. Our fingertips are quite sensitive, for example, but “it’s hard to compare the sensation arising from a movement of a whisker in comparison to touching my fingertip.” What’s certain is that humans aren’t nearly as sensitive to these electric fields as dolphins. Tim Hüttner, a behavioral biologist and research assistant at the Nuremberg Zoo, says he once put his hand in the water as the electric field moved through it and couldn’t feel a thing.
And dolphins also aren’t alone — platypuses and sharks also have electroreception. A platypus bill is full of receptors even though they reside in freshwater where Dehnhardt says animals don’t need to be as sensitive to the fields because of how salt interacts with them.
Dehnhardt also says that external factors can interfere with dolphins’ electrosense. Sun storms, for example, which have a strong electromagnetic effect on the Earth, can affect this sense during migration. That’s because electric fields create a “kind of magnetic map,” he says, and a sunstorm can actually meddle with how they interpret those maps. Human-made structures, too, like undersea cables, have been known to interfere with animal behavior.
Dehnhardt’s next challenge is figuring out how animals interact with these fields as they’re swimming since Donna and Dolly were only tested when stationary. This is particularly important as migrating dolphins can travel upwards of 20 miles a day on average, so scientists need to understand how electroreception impacts these majestic marine mammals while traveling.
Dolphins have been long known as the brainiacs of the sea, and this newly discovered electroreception just might push that intellectual accolade beyond reproach.
