Illustrated is a nanorobot crawling along a DNA track. Words with “nano” usually refer to things as small as individual atoms or molecules. Credit: Nicolle Rager Fuller

In 1966, scientists found a way to shrink anything — at least, they did in the movie Fantastic Voyage. In that film, a submarine and its crew were shrunk and injected into the body of a man. The man had been shot and was dying, and the tiny sub propelled around in his body in an attempt to save his life. The micro-crew did save his life, and the bad guy was eaten by a white blood cell. (Sorry for spoiling the ending.)

That movie was fiction — and far-fetched. A white blood cell will never consume a human being. It is true, however, that scientists are building tiny tools that will help in exploring the smallest parts of the real world. Some of these tools are called nanorobots, and in recent years researchers have been building nanorobots out of a familiar material — the same stuff that makes human life possible.

These nanorobots are built out of DNA, or deoxyribonucleic acid. (Words with “nano” usually refer to things as small as individual atoms or molecules.) DNA is literally all around (and in) you —you just can’t see it. If you were to look inside almost any cell inside any living creature, you would find DNA.

These nanorobots are made of DNA, and they “crawl” on DNA. (So sometimes researchers refer to these things as DNA “spiders.”) Being able to make such a tiny thing move in a certain way might be useful for health: A nanorobot could, perhaps, destroy just a cancerous cell, for example, but leave healthy cells alone.

DNA contains the basic directions for how to build the molecules that make life possible. From far away, a molecule of DNA looks like a jumbled mess. But up close, DNA looks like a spiral staircase. Each step of the staircase has two parts that are joined in the middle.

If you were to somehow break that spiral staircase apart, you’d have two curving sides with unconnected steps hanging off. (The steps are called bases.) Now imagine you have three or four of these DNA half-staircases, all connected at the top and dangling below.

Those half-staircases give you a simple picture of the legs of a DNA nanorobot. Each leg is made of half of a piece of DNA.

In the 1966 movie, a submarine is shrunk down small enough to go into a man’s bloodstream. Credit: 20TH CENTURY FOX / THE KOBAL COLLECTION

These ‘bots can’t walk on just any surface, but they can walk on other pieces of DNA. Scientists have found ways to fold the long, spiral molecules of DNA into other shapes: happy faces, for example and, more importantly, long tracks for the nanorobots. In a recent study, a DNA ‘bot took 50 “steps” across a track.

This might sound surprising — especially since these machines don’t need batteries or any power source. Instead, they work by using the natural structure of DNA.

Along the track are strands of DNA that stand up like hairs. These strands are attached to the track at the bottom. Just like the robot’s legs, the tracks are made of half-pieces of DNA — they resemble half-staircases with lots of broken steps. But while the spider DNA legs dangle down, the strands are attached to the track and rise up above it.

The DNA robot has half, and the track has half — so when the halves meet up, the stairs may join together. (Not always – these “stairs” must be carefully built.) This join-up is like a step for the tiny robot, and each leg can join with a floating strand from the track — the two fit together like puzzle pieces.

“The more legs you have, the stickier spiders are and the more steps they can take,” Milan Stojanovic told Science News. Stojanovic is a chemist at Columbia University in New York City, and he built the DNA nanorobot that took 50 steps.

To pick up its legs and take another step, the nanorobot has another molecular compound attached that acts like scissors. It snips the DNA strand on the track. Then, the whole staircase that had formed when the robot’s leg attached to the strand comes apart again, and the nanorobot’s leg is free — to go join up again with another free-floating piece of DNA attached to the track. In other words, the DNA nanorobot destroys the track as it goes.

“An automobile that chewed up the road behind it would be a bit unpopular,” Andrew Turberfield told Science News. Turberfield is a physicist at the University of Oxford, and he wants to build a reusable track for these tiny machines.

Nanorobots made from DNA aren’t useful yet, but they are impressive in the laboratory. One day, perhaps DNA-made machines will swim around in the human body, delivering medicine to diseased cells or helping doctors diagnose problems. Or maybe they’ll help build the smallest computers the world has ever seen.

The future is bright for DNA-built nanorobots, but one thing is for certain. We’ll never be able to shrink submarines to the size of cells, no matter what we see in the movies.

POWER WORDS

nano- Extremely small. One-billionth. (For example, one billion nanometers fit into one meter.)

robot A mechanical device capable of performing a variety of often complex human tasks on command or by being programmed in advance.

DNA A molecule that carries the genetic information in the cell and is capable of self-replication. DNA consists of two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds between the bases. The sequence of nucleotides determines hereditary characteristics.

nucleotides Any of various compounds consisting of a nucleoside combined with a phosphate group and forming the basic constituent of DNA and RNA.

The cells in Drosophila melanogaster that produce pheromones are located in the abdomen. Here, the cells are marked by a green fluorescent protein.

View a video of fruit flies displaying unusual courtship behavior.

Fruit flies linger over a bowl of rotting fruit. To untrained eyes, the flies may look like a swarming nuisance, but scientists have found that flies’ swoops and buzzes are ways to send signals through the crowd. Another, less obvious way these insects communicate is through chemical signals called pheromones. (It’s easy to think of these chemical signals as being similar to smells.)

Scientists have long known that pheromones may play an important role in reproduction — certain pheromones may attract a potential mate, for example. But in a surprising new study, scientists found that male fruit flies are particularly attracted to other flies — male and female — that don’t put out any pheromones at all.

The researchers also found that fruit flies without pheromones are attractive to males of other species. This research suggests that pheromones may be even more complicated — and important — than scientists thought. Besides telling other insects to come a little closer, pheromones may also be used to say, “Back off!” That message is important for keeping up barriers between species.

There are many different types of fruit flies, no matter how similar they all look as they swarm over a rotting tomato. Scientists have wondered how fruit flies can tell each other apart. Appearance may play a role. So may sound — the mating song of each different kind of fruit fly is different, for example.

Scientists suspect pheromones may also help fruit flies find potential mates of the same species — but there are 30 or more pheromones to choose from. In the new study, which was led by Joel Levine, the scientists wanted to figure out what messages the different flavors of pheromone were each sending. Levine is a neurogeneticist at the University of Toronto at Mississauga. (Neurogenetics is the study of how genes affect the development and function of the brain and the nervous system.)

His team genetically altered fruit flies so that the flies no longer made pheromones. Then the researchers watched the mating behavior of the insects, and observed that males went after the flies that didn’t have pheromones.

“Males are only after one thing. They want to mate,” Levine told Science News. Females, on the other hand, preferred males with pheromones to the males without. “She will not go for the guy who has no odors,” Levine said. He and his team also used the scentless flies as a starting point for other experiments. They were able to identify one particular pheromone, for example, that kept flies of different species from breeding.

These chemical signals help flies tell males from females, and help tell members of different species from each other. The new research suggests that pheromones may be more important than sight or sound in that crowd of flies hovering over the fruit bowl. “We expected the chemicals would play a role,” Levin said, but “we had no reason to think that the effects we saw would be so strong.”

Strange Attraction from Science News on Vimeo.

In the absence of pheromones, flies engage in unnatural courtship behavior. In this movie, two males attempt copulation with each other’s heads.

Credit: Jean-Christophe Billeter et al, Nature 2009

Going Deeper:

I had scanned a large, plant-filled enclosure several times before locating him: a 70-something-year-old tortoise named Lonesome George. The tortoise weighs 88 kilograms (nearly 200 pounds), but he was barely visible beyond several bushes, and his head and legs were tucked neatly within his shell.

An adult Galápagos tortoise lumbers within a semiprotected space at a breeding facility on San Cristobal Island.

Bryn Nelson

Like a stubborn child who refuses to leave his room, George is not the most sociable tortoise in the world. But he’s by far the most famous, and I was happy to spot him—or at least his shell. That’s because George is the last known member of his species, sometimes called the Pinta tortoise.

A special place

George lives in the Galápagos Islands, a group of 19 islands in the Pacific Ocean about 600 miles (a little less than 1,000 km) west of Ecuador. The islands are famous for their unique plants and animals. For example, many of the islands’ lizards, iguanas, tortoises, sea lions, seabirds, land birds called finches, and even a type of penguin, have been found nowhere else in the world.

Recent reports, however, suggest that many species in the Galápagos are in trouble. Scientists blame the growing problem on too much tourism, too many people moving to the islands, and the introduction of foreign plants and animals that are crowding out or killing native species.

Based on satellite photographs taken by NASA, this image shows the major islands in the Galápagos.

Wikipedia/NASA

But researchers and volunteers are working hard to save threatened animals such as the tortoises. Using a range of strategies, from radio collar–wearing goats to analyses of old tortoise bones, they are making a difference—and showing that a shy survivor named George may not be so alone after all.

The rarest creature

Before humans first arrived in the Galápagos Islands in the 1500s, 15 or more closely related tortoise species may have lived there. Twelve of those species still inhabit the islands, but two are extinct. Lonesome George is the last known member of the third.

A Galápagos tortoise shares a morning bath with a white-cheeked pintail in a duckweed-covered pool in Santa Cruz Island’s highlands.

Bryn Nelson

Scientists found George living alone on an island in the Galápagos called Pinta Island in the early 1970s. Because he is the last remaining Pinta tortoise that scientists know about, the Guinness Book of World Records has called him the “rarest living creature.”

I recently took a weeklong voyage through the Galápagos aboard a motor-powered yacht named the Letty. Aboard the boat, I met wildlife photographer Tui De Roy, who told me that several tortoise species were in even worse shape when she was a girl.

De Roy moved to the Galápagos Islands when she was 2 and lived there for more than 35 years. Now a resident of New Zealand, she helps oversee the Charles Darwin Foundation.

The foundation operates the Charles Darwin Research Station on Santa Cruz Island in the Galápagos. Scientists at the station advise the Ecuadorian government on how best to protect the Galápagos Islands.

By some estimates, De Roy says, up to 500,000 tortoises were killed for food or taken away as pets in the centuries before concerned people began protecting them. By the time preservation efforts began, perhaps only one-tenth of the original population remained.

Laws now protect the tortoises from hunting, but the lure of money still drives some people to kill the tortoises and sell their meat. Galápagos tortoises also face new dangers from animals that didn’t originally live on the islands, including goats.

Pesky goats

Over the past few centuries, fishers, pirates, sailors, and settlers brought goats to the Galápagos as a reliable food source. Unfortunately for tortoises, goats like the same types of grasses, fruits and leaves as tortoises do, and the goats are faster movers.

As the goats multiply, they beat tortoises to prime grazing spots. And they trample other favorite tortoise foods, like young prickly pear cacti.

As they stomp around, the hoofed animals can also squash sandy areas near the shoreline where tortoises build their nests. Over time, huge herds of goats can turn leafy forests into barren grassland.

This mural on the island of San Cristobal reads, “These introduced vertebrate animals are a menace in the Galápagos.” Pictured are a rat, cat, dog, pig, and goat—among the most destructive newcomers in the Galápagos Islands.

Bryn Nelson

Researchers have used helicopters, dogs, and even other goats to track down the goat invaders. The tracker goats wear radio collars that allow scientists and hunters to follow them as they mingle with wild goats. The researchers also put bright paint on the tracker goats, so hunters know to leave them alone but to nab their wild companions.

Goats be gone

The antigoat campaign has been paying off. Last year, researchers removed the last of an estimated 75,000 to 125,000 wild goats from the northern part of Isabela Island, which boasts more tortoise species than any other island in the Galápagos.

The victory built upon earlier successes on several other islands. On an island named Española, thousands of goats were removed in the 1970s, De Roy says. By then, the island’s native tortoise population had dwindled to 12 adult females and 2 males.

In the 1960s and early 1970s, researchers evacuated those few surviving tortoises to the Charles Darwin Research Station some 60 miles away. There, they set up an emergency-breeding program.

This male tortoise was once kept illegally as a pet. Now, he stretches out at the Charles Darwin Research Station on Santa Cruz Island.

Bryn Nelson

A third male tortoise from Española, named Macho, was already living at the San Diego Zoo. Scientists later brought him to the research station to help restore the island population. The descendants of Española have now helped resettle more than 1,400 tortoises on their goatfree native soil.

“Española is one of the most beautiful stories” of tortoise success, says Gisella Caccone, an evolutionary biologist at Yale University.

A stunning find

Earlier this year, Caccone and her colleagues announced another stunning discovery: Lonesome George may not be alone after all.

The discovery began with a routine study of the genetic material known as DNA. Every animal’s DNA is different, but researchers can look for common patterns among members of the same species that distinguish them from other species. A crow’s DNA, for example, looks significantly different from a hawk’s DNA, even though both creatures are birds.

First, Caccone’s team extracted a sample of DNA from George’s blood. The researchers also took DNA from the bones of long-dead Pinta tortoises that had been stashed away in museums for decades. By looking at samples of both living and dead specimens, the scientists came up with a profile of a typical Pinta’s DNA.

Next, the team compared the Pinta DNA with DNA from tortoises living on neighboring Isabela Island. They already knew the Isabela population had a mixed heritage, and they wanted to know more about where the ancestors of the Isabela tortoises had come from.

Their results surprised them. One young Isabela male tortoise, the scientists learned, shared half of George’s DNA. Caccone says that this discovery suggests that the youngster’s mom was likely born on Isabela Island. But his dad, like George, originally lived on Pinta Island, about 50 miles away.

No one knows how the tortoise father made the trip to Isabela. It’s possible that he and others rode to their new home with sailors or settlers, or on strong ocean currents. Unlike sea turtles, tortoises live only on land. Even so, tortoises have been known to survive for long periods in the ocean, whether floating by themselves or clinging to mats of vegetation. Some researchers, in fact, believe the first tortoises to arrive in the Galápagos Islands did so by floating westward from the mainland.

Either way, the new find has researchers hoping they’ll be able to identify more Pinta tortoises now living on Isabela—or at least tortoises that are partly descended from Lonesome George’s extended family. If they can find both males and females with Pinta DNA, scientists will start a new breeding program to pass on as much of that unique DNA to tortoise hatchlings as possible. If they’re really lucky, their breeding program may help the Pinta species survive. George, who seems completely uninterested in reproducing, would be off the hook.

These tortoise hatchlings are a few years old. Here, they seek shelter from the heat at the Charles Darwin Research Station on Santa Cruz Island in the Galápagos. Researchers have bred these hatchlings in captivity and will release them into the wild

Bryn Nelson

Caccone’s group has done more than revive the hope of rescuing Pinta Island tortoises from the brink of extinction. Two years ago, the team also discovered a previously unknown species of tortoise on Santa Cruz Island, where most people in the Galápagos Islands live. The isolated population of about 100 tortoises still doesn’t have a formal name.

“The Galápagos can yield an incredible amount of new surprises,” Caccone says. “Think what you can find when you really study well the other islands.”

Going Deeper:

News Detective: A Galápagos Journey

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It doesn’t take long before a hive is nearly empty. Researchers call this phenomenon colony-collapse disorder. According to surveys of beekeepers across the country, 25 to 40 percent of the honeybees in the United States have vanished from their hives since last fall. So far, no one can explain why.

Inspecting a honeycomb from a healthy hive (above), beekeeper Dan Geer finds bees densely packed. A honeycomb from a hive whose colony is collapsing (below) has far fewer bees.

Cutraro (both images)

Colony collapse is a serious concern because bees play an important role in the production of about one-third of the foods we eat, including apples, watermelons, and almonds. As they feed, honeybees spread pollen from flower to flower. Without this process, called pollination, a plant can’t produce seeds or fruits.

Now, a group of scientists and beekeepers has teamed up to try to figure out what’s causing the alarming collapse of so many colonies. By sharing their expertise in honeybee behavior, health, and nutrition, team members hope to find out what’s contributing to the decline and to prevent bee disappearances in the future.

Sick bees?

It could be that disease is causing the disappearance of the bees. To explore that possibility, Jay Evans, a research entomologist at the United States Department of Agriculture (USDA) Bee Research Laboratory, examines bees taken from colonies that are collapsing. “We know what a healthy bee should look like on the inside, and we can look for physical signs of disease,” he says.

And bees from collapsing colonies don’t look very healthy. “Their stomachs are worn down, compared to the stomachs of healthy bees,” Evans says. It may be that a parasite is damaging the bees’ digestive organs. The bees’ inability to ward off such parasites suggests that their immune systems may not be working as they should.

The honeybees have other signs of troubled immune systems, such as high levels of bacteria and fungi inside their bodies, says Dewey Caron, an entomologist at the University of Delaware. He’s one of the leaders of the colony-collapse research team.

But why would parasites, bacteria, or fungi in the body cause bees to leave their hives? After all, when you’re sick, you want to stay at home, right?

Caron says that some of these disease-causing agents may lead to disturbances in bee behavior. “It may be that sick bees are not processing information correctly and learning where home is,” he says. In other words, a sick bee might leave the hive and simply forget how to get back.

If enough of the bees in a colony can’t find their way home, he says, it’s just a matter of time before the colony collapses. Being social insects, even healthy bees are unable to live long on their own. And once the bees vanish, the crops that they usually pollinate are in trouble.

Environmental clues

Another cause of colony-collapse disorder may be certain chemicals that farmers apply to kill unwanted insects on crops, says Jerry Hayes, chief bee inspector for the Florida Department of Agriculture. Some studies, he says, suggest that a certain type of insecticide affects the honeybee’s nervous system (which includes the brain) and memory. “It seems like honeybees are going out and getting confused about where to go and what to do,” he says.

Adding to the mystery, Hayes says, is an observation about moths and other insects that frequently use empty beehives to raise their own young.

“Usually, they move right into an empty hive,” he says, “but now they’re waiting several weeks before they do.” As Hayes sees it, this suggests that something repellent in the hive may not only be driving out bees but also keeping other insects from moving in, he says. So far, scientists haven’t identified what that repellent thing could be.

Looking at bee genes

If it turns out that a disease is contributing to colony collapse, bees’ genes could explain why some colonies have collapsed and others have not. In any group of bees—or other animals, including people—there are many different kinds of genes, because each individual has a slightly different unique set of genes. The more different genes a group has, the higher the group’s genetic diversity. And genetic diversity is a plus as far as survival is concerned.

Some scientists are now studying genetic diversity in honeybee colonies to see if it has an effect on colony collapse disorder.

“If a colony is genetically diverse, it’s less likely the colony will be wiped out completely from a sweeping infection or disease,” says David Tarpy, a University of North Carolina entomologist. That’s because at least some bees in a genetically diverse group are likely to have genes that help them resist any specific disease that gets into the colony, he says. Scientists haven’t determined the role of genetic diversity in colony collapse, but it’s a promising theory, says Evans. He and his colleagues at the USDA bee lab are currently running genetic tests on bees from collapsing colonies. Their goal is to find out whether there are genetic differences between the bees that vanish and those that remain in their hives.

Beekeeping helps support these important, pollinating insects.

Cutraro

Scientists are working hard to figure out the causes of colony collapse. Meanwhile, bees continue to disappear. Can anything be done to help them survive?

Tarpy suggests that more people could raise bees to help restore their numbers. “Given this decline in honeybees, if you want to get active in helping to promote pollination, the best thing to do is to become a beekeeper and keep your own bees,” he says.

Don’t be put off by the possibility of a sting, says Dan Geer, who raises bees in North Smithfield, Rhode Island. First of all, beekeepers can wear protective gear. And bees, he says, have a bad rep. “You’d be surprised by how gentle they are,” he says.

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Going Deeper:

Silk threads can be dyed bright colors and then woven into beautiful fabric.

iStockphoto

Since then, researchers have unraveled many of silk’s mysteries, but they still don’t fully understand how silkworms, spiders, and other small creatures create what turns out to be one of the toughest materials known.

Silkworms weave silk into white cocoons.

iStockphoto

But Ann Terry, a physicist and a visiting professor at Oxford University in England, thinks that she and other researchers are closing in on that remaining mystery. Terry and other experts hope that current research into silk will lead to a new generation of fabrics that are lightweight and superstrong. Such materials would be useful for medical and military purposes and also could help astronauts and clothing-makers.

Strong stuff

The silk industry still depends on silkworm silk, but scientists have lately focused their attention on spider silk because it’s much tougher. (Toughness describes how much energy it takes to break a material.)

Spiders use a particularly tough type of silk to form the “arms” of their webs. These arms, like spokes of a wheel, run outward from the center of the web, where the spider in this photo is.

iStockphoto

Spiders can spin different types of silk, some of which are tougher than others. In a classic orb web (like the kind you’d expect to see in a haunted house), the toughest type of silk forms the arms of the frame. These arms, like spokes of a wheel, stretch outward from the center of the web, says Gareth McKinley, a scientist at the Massachusetts Institute of Technology in Cambridge. Another type of silk, which is sticker, forms the spirals that connect the arms of the frame. This sticky silk helps the spider capture its prey.

Spider silk can be “strong stuff,” McKinley says. To test silk’s strength, scientists hang weights from the frame threads of an orb web, then measure how much weight those threads can hold. The researchers have found that spider silk can be as much as 100 times tougher than the same amount of steel. It is about twice as tough as Kevlar, a synthetic fiber used to make sturdy objects such as bulletproof vests and boats.

Slippery and sticky silk

Spider silk starts out as a goopy, yellowish liquid inside the animal’s body. So, how do silk-spinning creatures turn this liquid into one of nature’s toughest solids?

To better understand how that happens, McKinley and colleagues tested two properties of spider silk: slipperiness and stickiness. To test slipperiness, they used a microscopic device that mimicked the motion of a thumb and forefinger sliding back and forth against each other, with a glob of liquid in between. The stickiness test mimicked a thumb and forefinger pulling a glob apart over and over again.

Shawna Liff, a graduate student at the Massachusetts Institute of Technology, works with a synthetic material that is similar to spider silk in its strength and stretchiness.

Donna Coveney/MIT

Sliding the glob quickly, the researchers found, made spider silk 30 times as slippery as it was to start with. And pulling made it more than 100 times as sticky.

Those results help explain what happens when a spider squeezes out liquid silk through the narrow channel in its abdomen. First, the silk becomes slippery. This allows the silk to flow more easily as the spider excretes it. It’s so sticky that the spider can hang from it—like a person dangling from a bungee cord. When clinging to a strand of silk, a spider can change how fast it drops by varying how quickly it draws out its silk, McKinley says.

This microscopic picture shows what happens when a synthetic material that’s like silk gets stretched. The stretched part of the material is near the bottom of this picture. It appears to be brightly colored because the molecules are lined up.

Courtesy of Gareth McKinley Lab/MIT

Scientists have already figured out how to extract liquid silk from a spider’s body and to use it to spin fibers. But these human-made threads are never as tough as the ones spiders spin on their own, Terry says. Scientists are still trying to figure out exactly why. They’ve found out, for example, that the protein molecules that make up the silk line up and form parallel chemical bonds inside a spider’s body. This adds an extra measure of toughness, Terry says. Spiders regulate the amount of water and other molecules that go into their silk supplies, which can also affect the silk’s quality.

Supersilk soon?

Unfortunately, farming spiders for their silk is impractical because the creatures produce only very small amounts of liquid. They are also too territorial to tolerate living closely with other spiders. Silkworms are easier to breed and keep in captivity.

The spinning process that silkworms use may explain why their silk isn’t as tough as spider silk. Unlike spiders, which draw silk out of their abdomens, silkworms draw silk out of their mouths. They move their heads in a figure-eight pattern as they do this. In a recent study in which researchers kept the worms’ heads from moving, the worms produced fibers that were just as tough as spider threads.

This finding suggests that silk manufacturers might someday be able to use the silk from silkworms to make spider-strength thread.

Researchers are also looking for more efficient ways to make silk. Some experiments have involved inserting the spider’s silk-making gene into alfalfa, goats, and other organisms to have them produce silk proteins. These proteins could then be harvested and spun into silk.

Ultimately, understanding the biology of the silk-making process and the physical qualities of silk should help researchers make even better materials, Terry says. Knowing how each factor affects the final product will give scientists more control over the process. And that control could open a wealth of potential uses for silk—from the manufacture of lighter, stronger protective gear to the ability to help repair torn ligaments in people.

Spiders make silk spinning look easy, but they’ve had millions of years to figure it out.

“Nature still beats us,” Terry says. “We have a lot to learn from nature.”

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