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When it dives, the platypus closes its eyes, ears and nostrils and finds its food through electrical receptors in its bill that detect the movement of small prey. (Photo courtesy of Nicole Duplaix/Getty Images)

On the Evolutionary Gold Mine Down Under

What the platypus and other Australian species reveal about genetics

smithsonian.com

(Continued from page 1)

The kangaroo is the second marsupial to be sequenced. The genome of a South American species of opossum was published last year. The scientific community has published twenty mammalian sequences up until now, but that number is expected to increase dramatically as a result of technological advances and international cooperation. After the platypus and the kangaroo, the echidna could well be the next Australian native (it is also in New Guinea) to undergo genetic decoding. ARC Australian Research Fellow Frank Grützner of Adelaide University, who also participated in the platypus project, has been equipping some echidnas with radio transmitters and taking their DNA for sequencing.

But it's not just mammals that are receiving genetic scrutiny. Graves's lab is also looking at alligators, birds such as the emu, and even the nearly extinct corroboree frog.

"The genomics age has really been exciting for us who work on weird animals," she says. "We couldn't be happier."

Weird is certainly the term for the platypus—an Aboriginal legend maintained it was the offspring of a duck and a water rat—but evolution has equipped it nicely for its semi-aquatic lifestyle. Its flat tail acts as a rudder when it swims and is also a storage area for extra food. Its webbed front feet extend to aid in swimming, but on land fold back, allowing the claws to become spades for digging burrows in earth banks around rivers, lakes or streams. When it dives, it closes its nostrils as well as its eyes and ears (it has no outer ear lobe). But its flat bill locates food through unique electrical receptors that detect movement made by small prey such as insect larvae, shrimp and dragonflies.

The platypus is a real loner: mating is its only social interaction. Staff at South Australia's Warrawong Wildlife Sanctuary near Adelaide who have witnessed the mating ritual describe it as a ten-minute water dance, with the male initially holding the female's tail in his mouth as they swim and dive through the water. After mating, each partner returns to its burrow.

"I think the whole rational of using comparisons between distantly related animals to tell us about our own genomes is sometimes a bit lost in the ‘gee-whiz, how weird' aspects of the platypus genome," says Graves. "Comparative genomics is a terribly powerful strategy for exploring our own past."

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