 Hones in on Prey
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Dec. 17, 2003 — The bills and brains of duck-billed platypuses are specially equipped with electro-sensors to home in on the electrical signals of prey in muddy night-time stream bottoms, say Australian biologists.
A row of nerves in platypus bills, wired to the touch and electro-sensing part of the platypus brain, work like a short-range radar system to pick up the electrical signals of fish, shrimp, crayfish and other invisible food in the murky platypus feeding grounds.
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The sensory system is just one more remarkable asset for the egg-laying, aquatic Australian mammal.
"What's curious is that the system in the platypus evolved entirely independently," said Uwe Proske of Monash University in Victoria, Australia.
Proske and Ed Gregory published the latest speculations about platypus electro-receptors in this month's issue of Comparative Biochemistry and Physiology.
The first time the underwater stealth-busting system evolved was in sharks, rays and other non-bony fish, said neuroscientist and electric fish researcher Curtis Bell of the Oregon Health and Science University. The second time was in certain electric bony fish and some amphibians. The third time was in platypuses.
Because platypuses had to evolve the system from scratch, it looks like they adapted touch receptors — not unlike what we humans have in our skin — to do the job. What really gives this away is that the electro-receptors in platypus bills are connected to the touch-processing part of platypus brains.
As a result, that part of the brain has also grown to meet the new challenge. "It's a huge part of the brain," said Proske.
The way the electro-receptors work is analogous to sonar or radar, Bell said. The nerves in the platypus bill send out a weak electrical field that is altered when a shrimp, crayfish or fish, all with electrical signatures of their own, comes within two to four inches.
The electro-receptors are so sensitive that platypuses can capture half their house-cat-sized body weight in prey every night — in muddy water, at that.
"It's a very useful sense in the aquatic environment," said Bell, but is useless in the air, since air doesn't conduct electricity as well as water.
In fact, that's why platypuses had to recreate the electro-sensory system for themselves: their evolutionary ancestors were not aquatic, and so they had no use for electro-sensors.
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Name: Duck-Billed Platypus (Ornithorhynchus anatinus)
Primary Classification: Ornithorhynchidae (Platypus) Location: Eastern Australia and Tasmania. Habitat: Streams, lakes, and other freshwater systems. Diet: Insect larvae, freshwater shrimp, mollusks, frogs and fish eggs. Size: Up to 18 inches in length and 4 lbs in weight. Description: Plum-colored body fur; duck-like, beak-shaped mouth; flat, streamlined body; fully webbed front feet; partially webbed back feet; flattened, beaver-like tail. Cool Facts: The male has poisonous glands embedded in his thighs that are connected to spurs on his ankles; when he fights with another platypus or a predator, he can puncture his opponent with a spur, injecting the animal with poison. Conservation Status: Not listed by the IUCN. |
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