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ODD-LOOKING PLATYPUS AND ECHIDNA DELIVER SHOCKER

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Two of the world's oddest creatures, the platypus and its cousin, the echidna, are giving scientists a shock - literally.

Their research has revealed that these strange creatures have a sixth sense: Both can detect tiny electrical fields, a power they use to find their prey.The discovery adds a new twist to the already baffling story of the platypus and the echidna, two animals that make up a unique class of mammals known as monotremes. Found only in Australia, platypuses and echidnas lay eggs instead of giving birth to live young as do all other mammalian species. Only after their eggs have hatched, about 10 days after being laid, do mothers suckle their young.

So unusual is this behavior that when specimens of the platypus were sent to Britain in 1798 from Australia, they were widely considered to be fakes, made by stitching the bill of a duck to the body parts of a mammal. Since then, scientists have endeavored to uncover the origins of the strange creatures with little success, although they now know that the platypus and the echidna have thrived in Australia for at least 15 million years.

However, recent research in Canberra on the platypus provided the real surprise. These amphibious animals, with their pliable duck-like bills, thick fur and strongly webbed forefeet, thrive over much of eastern Australia. The platypus (Ornithorhynchus anatinus) lives in river-bank burrows and dives for food - mainly shrimps, larvae, worms and other tiny creatures. However, biologists were baffled when they found that platypuses usually do this with their eyes closed and their earflaps tightly shut.

Then researchers made a remarkable discovery. They found that platypuses investigated live batteries left in their cages but ignored dead ones. Further experiments revealed that platypuses could learn to avoid transparent objects left in their pools when an electrical field was generated around it but would bump into these objects when the field was turned off.

Subsequent research revealed that the platypus has millions of thick nerves that run into its brain, carrying sensory information from receptors along its bill. These receptors, shaped like microscopic rose buds, are extraordinarily sensitive: They can detect currents as weak as two ten-thousandths of a volt.

This impressive feat helps the platypus detect food because creatures such as shrimps generate oscillating electric fields when their tails flick, and the platypus's receptors are tuned exactly to detect such a field.

The movements of other prey, such as fishes, earthworms and insect larvae, probably generate detectable electric fields in a similar way. When underwater, the platypus is known to move its head from side to side, which suggests it is scanning, rather like a radar scanner, for food.

Scientists then started wondering about the echidna. In fact, there are two species of echidna: the long-beaked New Guinea echid-na (Zaglossus bruijnii) and the short-beaked Australian version (Tachyglossus aculeatus). Similar to the platypus in internal biology, they share the characteristic egg-laying, baby-suckling habits of all monotremes but have adapted to living on land.

Echidnas, which eat termites, ants, worms and other insects, have lengthy snouts, long tongues and sharp, spiny coats that act as defenses against predators.

Recently researchers made a key observation about echidnas: They have perpetually runny noses. Could that have something to do with the detection of electricity which, after all, flows best in wet conditions? To find out, scientists put short-beaked echidnas in cages and placed food in water troughs in which electrical fields were generated. The echidnas came to associate food with these fields and would seek something to eat there when the current was switched on. But when the field was switched off, they simply wandered away.

These experiments showed that, just like the platypus, the echidna has receptors at the end of its snout for detecting electricity. But why has the echidna evolved this sophisticated attribute? After all, it does not hunt in water where fish easily generate tiny electric currents.

Possibly, they can detect tiny electric currents set up by beetle grubs and other prey as they move around deep in their nests. However, Australian scientist David Morgan suggests a stranger idea - that the echidnas' snouts are coated with chemicals that react with the gas, methane. This generates a tiny electrical current when methane is present, and this reaction can be detected by the echidna's receptors. In other words, the echidna's snout is a highly efficient gas detector.

But what could be the purpose of such a detector? The answer is simple: Termites, the echidna's favorite food, emit methane, an otherwise odorless gas. By evolving highly sensitive methane detectors, echidnas are able to home in on some of their favorite foodstuffs.