Archilider via LiveScience.com
The Guiana dolphin (shown here) has the ability to sense electric fields, likely helping the aquatic mammals find prey in their murky habitat.
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updated 7/26/2011 9:45:08 PM ET 2011-07-27T01:45:08

The common Guiana dolphin has just divulged its sixth sense: the ability to sense electric fields. It is the first placental mammal known to pull off this trick, new research finds.

The dolphin, which bears live young like other placental mammals, most likely uses its sixth sense to find prey in the murky coastal waters it inhabits.

"Most of the animals which do this do this to find prey," said study researcher Wolf Hanke, of Rostock University in Rostock, Germany. "All of the dolphins' prey items, like crayfish, all of them generate electric fields to some degree."

The Guiana dolphin looks like the familiar bottlenose dolphin; it is only slightly smaller. It lives close to estuaries, inlets and other protected shallow waters off the north and eastern coasts of South America.

Electrifying the senses
The researchers examined a Guiana dolphin that had died naturally at the Dolphinariumin Münster, Germany. They focused on specialized pores called vibrissal crypts, which in other animals are located in hair follicles at the bottoms of their whiskers, allowing the animals to sense movement using their whiskers. Through evolution, the dolphins have lost their whiskers, but kept the pores.

They found that the specialized pores — which usually number from two to 10 along the dolphin's snout — are surrounded by nerve endings, have simplified blood vessels and are filled with a special matrix of proteins and cells. The pores also produce a gel-like substance.

To see if these pores react to electric fields, the researchers performed some tests on a live dolphin from the facility. They trained it to react to electric fields by giving it a treat when it correctly sensed the field or lack of field. They tested different strengths of fields; the animal sensed the field correctly most of the time at a very low level — 5 microvolts per centimeter — lower than the level produced by a typical electric fish.

Exceptional mammal
No other "true" placental mammal is known to have developed the ability to sense electric fields. Two members of the monotremes, a strange group of mammals that lays eggs (which includes the platypus), have also developed this ability. The quirky platypus and its cousin the echidnas (spiny anteaters) are semiaquatic and evolved the ability separately from the dolphins.

It's possible other marine mammals also developed the ability, Hanke said. "I think it's possible, it's likely, because there are some dolphins, like the bottlenose, that have little pits on its snout, too. They are smaller, but it's not unlikely that this one or other ones would develop it too," he said.

The electroreception would be used in short-range scenarios, when the dolphins' echolocation (ability to determine the environment around them using sounds and their echoes) becomes less sensitive. These waters are murky, so visibility is limited even at these short ranges, so being able to electrically sense their prey would help these dolphins feed.

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Carl Hopkins, a researcher from Cornell University in Ithaca, N.Y., who was not involved in the study, warns that several other studies about electroreception in animals have not been confirmed, and he would have liked to see a larger sample size in this study.

"The paper seems relatively convincing, but the sample size is very small and there really is only one study here, the behavioral assay, since the anatomy does not help with the issue of electroreception," Hopkins told LiveScience in an email. "If this holds up, it will be exciting to do follow-up work."

The study was published today (July 26) in the journal Proceedings of the Royal Society B: Biological Sciences.

You can follow LiveScience staff writer Jennifer Welsh on Twitter @microbelover. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

© 2012 LiveScience.com. All rights reserved.

Explainer: 10 secrets of the deep ocean

  • Mark Spear / Woods Hole Oceanogr

    The oceans cover more than 70 percent of the earth's surface, yet their depths remain largely unknown. It's a frontier that scientists are racing to explore using tools such as the deep-ocean submersible Alvin, shown here. Click the "Next" arrow above to learn about 10 deep-ocean secrets that have come to light.

  • Deep-ocean octopuses have Antarctic origins

    Image: Megaleledon setebos
    Census of Marine Life

    Many deep ocean octopuses trace their origins back to relatives that swam in the waters around Antarctica. The migration began about 30 million years ago when the continent cooled and large ice sheets grew, forcing octopuses there into ever deeper waters. The climate shift also created a northbound flow of deep, cold water that carried the cephalopods to new habitats. As they adapted to new niches, new species evolved. Many lost their defensive ink sacs because the pitch-black ocean depths required no camouflage screen. The species known as Megaleledon setebos, shown here, is the closest living relative of the deep-sea octopuses' common ancestor.

  • 'Brittlestar City' found on undersea mountain

    Census Of Marine Life  /  AP

    The orange and red starfish relatives called brittlestars have managed to defy the odds and colonize the flanks of a giant, underwater peak on the Macquarie Ridge, an 870-mile-long underwater mountain range that stretches south from New Zealand to just short of the Antarctic Circle. The peak, known as a seamount, juts up into a swirling circumpolar current that flows by at 2.5 miles per hour, delivering ample food for the brittlestars to grab while sweeping away fish and other would-be predators. Another brittlestar species has settled on the seamount's flat summit, a habitat normally settled by corals and sponges.

  • Deep Antarctic waters, cradle of marine life

    Wiebke Brokeland / GCMB

    This pale crustacean from the genus Cylindrarcturus is one of more than 700 species new to science found scurrying, scampering and swimming in the frigid waters between 2,000 and 21,000 feet below the surface of the Weddell Sea off Antarctica. The discoveries were part of a research project to determine how species at different depths are related to each other there, and to other creatures around the world. "The Antarctic deep sea is potentially the cradle of life of the global marine species," team leader Angelika Brandt, an expert from the Zoological Institute and Zoological Museum at the University of Hamburg, said in a statement announcing the discoveries.

  • Northernmost black smokers discovered

    Credit: Center for Geobiology/U. of Bergen

    Scientists working deep inside the Arctic Circle have discovered a cluster of five hydrothermal vents, also known as black smokers, which spew out liquid as hot as 570 degrees Fahrenheit. The vents are 120 miles further north than the closest known vents, which tend to occur where the seafloor spreads apart at a quicker pace. This image shows the arm of a remotely operated vehicle reaching out to sample fluids billowing from the top three feet of the tallest vent, which reaches four stories off the seafloor. The chimney is covered with white bacteria that feast on the freshly delivered minerals.

  • Black smoker fossils hint at life's beginnings

    Timothy Kusky / Gondwana Research

    The discovery of primitive bacteria on 1.43 billion-year-old black-smoker fossils – a crosscut is shown here – unearthed from a Chinese mine adds weight to the idea that life may have originated in deep-sea hydrothermal vents, according to geologist Timothy Kusky at Saint Louis University. The ancient microbe dined on metal sulfide that lined the fringes of the chimneys. The oldest-known life forms on Earth are 3.5 billion-year-old clumps of bacteria found in Western Australia. That find suggested that shallow seas, not the deep oceans, were the birthplace of life. Neither discovery, however, serves as the definitive answer about life's origins.

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    Once thought barren and sparsely populated, the deep-ocean floor is home to rich and diverse communities of bacteria. In fact, scientists have found that the seafloor contains three to four times more bacteria than the waters above, raising the question of how the organisms survive. Lab analyses suggest that chemical reactions with the rocks themselves provide the fuel for life. The discovery is another tantalizing hint that life could have originated in the ocean depths. In a statement about the find, the University of Southern California's Katrina Edwards said: "I hope that people turn their heads and notice: There's life down there."

  • Where do deep-sea fish go to spawn?

    Harbor Branch / E.widder

    Life in the dark, cold and vast depths of the sea was long thought to be lonely for the few fish that dared eke out an existence there, mostly from organic detritus that sinks from shallower waters. That picture began to change in 2006, when researchers probing the Mid-Atlantic Ridge discovered that fishes may occasionally gather at features such as seamounts to spawn. The evidence for these gatherings comes from the sheer volume of fish collected at seamounts – much higher than would have been expected if the fish were purely nomadic wanderers. What's more, images made from acoustical "scatterings" are suggestive of a massive fish aggregation. The 35-pound anglerfish shown here is one of the rare species hauled up from the deep during the project.

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    Image: New Zealand colossal squid
    Ross Setford  /  AP

    What did you expect? Would a colossal squid have anything but eyes big enough to generate a few over-the-top superlatives? Probably not - but still, when researchers thawed out this squid in New Zealand, the wow factor was undeniable. The creature's eye measured about 11 inches across; its lens was the size of an orange. Scientists suspect the big eye allows the huge squid to capture a lot of light in the dark depths in which it hunts. The squid weighed about 1,000 pounds when caught in the Antarctic's Ross Sea and measured 26 feet long. Scientists believe the species, which can descend to 6,500 feet, may grow as long as 46 feet.

  • Deep-sea corals record history

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    Rob Dunba  /  Stanford University

    Some coral reefs are found thousands of feet below the ocean surface, where they have grown amid frigid waters for millennia. Like tree rings, they serve as a faithful archive of global environmental change, according to Robert Dunbar, a professor of geological and environmental sciences at Stanford University. His team travels the world to collect samples of these corals, such as this one from a colony near Easter Island. In 2007, the team published a 300-year archive of soil erosion in Kenya, as recorded by coral samples collected from the bottom of the Indian Ocean. They are now analyzing 4,000-year-old corals discovered off Hawaii to create an archive of climate change.

  • Trawling destruction visible from space

    Sky Truth

    Some scientists are working urgently to expose more secrets of the deep ocean before unexplored treasures are plundered. Their biggest concern is the fishing practice known as bottom trawling. This image shows the billowing plumes of sediment left in the wake of trawlers dragging giant nets across the ocean floor in the Gulf of Mexico. The practice has been shown to strip coral reefs bare and ravage underwater ecosystems such as seamounts, where thousands of species are known to gather. Though the practice is increasingly restricted, tens of thousands of trawlers continue to ply the deep oceans.

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