A seedling of a vine known as dodder attaches to a tomato plant.

Photo by Justin Runyon (courtesy of De Moraes and Mescher Labs)

When a dodder seed sprouts, it doesn’t grow roots to seek its own food. Instead, it grows a shoot that reaches out to other plants, tapping them for food. The baby vine needs to find a host within a week to survive. It then grows into a spaghetti tangle that can even ensnare more than one plant.

Also known as strangleweed and witches’ shoelaces, dodders are listed among the 10 worst weeds in the United States. They can cost farmers millions of dollars by stunting their crops.

To figure out how a type of dodder vine known to prefer tomato plants finds a victim, scientists placed dodder sprouts near several possible targets. These targets included pots of moist soil, little jars of dyed water that created colored lights, young tomato plants, and even a cup of perfume made from chemicals that tomato plants give off.

A dodder tangle steals food and water from a glasswort plant.

Photo by Collin Purrington (courtesy of De Moraes and Mescher Labs)

Seedlings grew toward the tomato plant. They also reached out toward the cup of tomato perfume. They tended not to grow toward the moist soil or colored water.

The scientists then used a different setup, hiding the targets in chambers connected to dodder sprouts only by curving pipes, so the vine could find them only by smell. Dodder sprouts still grew toward their favored targets.

The tendril of a young dodder plant stretches out to entwine a tomato seedling.

Photo by Justin Runyon (courtesy of De Moraes and Mescher Labs)

By placing dodder sprouts near different plants, the scientists found that the type of dodder that they were studying prefers tomatoes and a flower called impatiens. And when given a choice between tomato and wheat, vine seedlings grow toward tomato.

The researchers then tested seven of the ingredients that make up tomato perfume separately. Dodder sprouts were attracted to three of them.

One of these ingredients turns up in wheat perfume, but the wheat perfume also contains a substance that repels dodder sprouts. This chemical could offer farmers one way to fight the vine and save their crops.—C. Gramling

Going Deeper:

Milius, Susan. 2006. Scent stalking: Parasitic vine grows toward tomato odor. Science News 170(Sept. 30):214. Available at http://www.sciencenews.org/articles/20060930/fob7.asp .

To learn more about research on dodder vines and how they respond to smell, see live.psu.edu/story/19800 (Penn State University).

To see a QuickTime movie of a dodder shoot growing toward a tomato plant, click here.

For additional information about dodder, go to
www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7496.html and
plants.usda.gov/java/profile?symbol=CUPE3.

Science project ideas: Do all types of dodder vines rely on smell to find their hosts? How do various types of dodder vines differ in their preferences for plant hosts? Do any other parasitic plants find hosts by smell?

Researchers have now found that microbes living under the ocean floor appear to produce propane and another gas called ethane. These microbes chew up ancient organic material, such as leaves and twigs buried in the sand, and they generate the gases as waste products.

That’s a surprise. Scientists had thought that propane and ethane could be produced only in the same way that petroleum is—by great heat applied to ancient, buried material.

Kai-Uwe Hinrichs examines a sample taken from a cylinder of sediment drilled out of the ocean floor.

Ocean Drilling Program Leg 201 Science Party

A team led by Kai-Uwe Hinrichs of the University of Bremen in Germany went on a research ship equipped with an enormous drill that dug out cylinders of sand or rock thousands of feet long. When the researchers examined these cylinders, they found traces of ethane and propane locked in the sediment.

Normally, to generate these gases, Earth’s heat cooks organic material in sand for many thousands of years. This can happen only at spots above cracks in Earth’s crust, where heat can leak out from inside Earth, and where thick layers of sediment would act like a blanket.

But the samples that Hinrichs and his coworkers had looked at contained thin layers of sediment. Some cylinders had also been obtained from places far from any cracks in Earth’s crust. So where could the gases be coming from?

Scientists already knew that microbes could break down organic material to produce a related, simpler gas called methane. So, undersea microbes were the only thing that made sense.

“When you can’t come up with any geologic source, then biology is an obvious candidate,” Hinrichs says.

The finding may someday lead to practical applications. Propane is valuable as a fuel, and ethane is used to make plastics. Pulling propane and ethane out of sediment is too difficult to be practical. But if scientists can better understand how microbes create the gases, they might be able to use the microbes’ methods to make ethane and propane directly from organic material.—J. Rehmeyer

Going Deeper:

Rehmeyer, Julie. 2006. Gassy bugs: Microbes may produce propane under the sea. Science News 170(Sept. 30):213. Available at http://www.sciencenews.org/articles/20060930/fob4.asp .

You can learn more about propane at en.wikipedia.org/wiki/Propane and ethane at en.wikipedia.org/wiki/Ethane (Wikipedia).

Cutraro, Jennifer. 2006. Microbes at the gas pump. Science News for Kids (April 12). Available at http://www.sciencenewsforkids.org/articles/20060412/Feature1.asp .

Sohn, Emily. 2006. Plant gas. Science News for Kids (Jan. 18). Available at http://www.sciencenewsforkids.org/articles/20060118/Note2.asp .

______. 2004. Drilling deep for fuel. Science News for Kids (Sept. 29). Available at http://www.sciencenewsforkids.org/articles/20040929/Note3.asp .

ScienceFairZone
Harvesting Biogas from Manure
www.sciencenewsforkids.org/articles/
20050504/ScienceFairZone.asp

For some songbirds, the trip may be as short as a jaunt from southern Wisconsin to Georgia. Other birds fly all the way from the northern forests of the United States and Canada to their winter homes in Central and South America.

But the gold medal for the longest migration flight doesn’t belong to a songbird. Instead, it rests with a small seabird called the sooty shearwater.

A sooty shearwater.

Darren Scott, University of Otago

A team of scientists recently found that this bird has the longest migration route of any species in the animal kingdom. Sooty shearwaters travel more than 64,000 kilometers (39,000 miles) in a single year. That’s about one-and-a-half times the distance around the globe at the equator.

Why the long flight? The birds follow an “endless summer” of food supplies around the Pacific Ocean, says biologist Scott Shaffer of the University of California, Santa Cruz.

“They go to areas rich with food each season,” Shaffer says. “They leave the Southern Hemisphere in the fall, stay in our hemisphere in the spring, and leave in the fall. They don’t ever experience a true winter.”

Food plays an important part in the migration both of seabirds, such as sooty shearwaters, and of songbirds, such as warblers and thrushes. Now, scientists are uncovering new details of how these birds manage to travel long distances over open water.

Efficient flight

Shaffer and his team tracked sooty shearwaters using data recorders attached to small bands encircling the birds’ legs. The devices record a bird’s position as well as the air temperature and pressure. This information helps researchers determine when and where the birds dive for food.

This map shows the travels of 19 sooty shearwaters during breeding and migration. Their tracks during breeding, near New Zealand, are shown in light blue. Yellow pathways represent their northward migratory routes. Orange lines show the birds’ wintering a

© PNAS

To power their impressive flights, sooty shearwaters rely on global ocean-wind patterns generated by waves, weather systems, and Earth’s rotation. “It’s like a conveyor belt of wind,” Shaffer says. “The birds get onto it, and it blows them westward.”

The birds also position their bodies to tack, as a sailboat does, moving at an angle to the prevailing wind direction, he says.

“These birds take advantage of all these winds and glide in a way that doesn’t cost them very much energy,” Shaffer says.

Biologist Scott Shaffer tags a bird.

Darren Scott, University of Otago

But shearwaters still need to eat a lot to fuel their long-distance travels. Their routes cover large parts of the Pacific Ocean, targeting places where food is abundant at any given time of the year.

Energy supplies

All migrating birds, not just shearwaters, need ample supplies of energy to support their lengthy travels, says Russell Greenberg of the Smithsonian Institution Migratory Bird Center. In birds, much of this energy is stored as body fat.

Warblers, thrushes, and other songbirds, for example, belong to a large group called neotropical migrants. These birds spend the spring and summer in the forests of northern North America. They winter in the forests of Central and South America.

In preparation for migration, the birds gorge on insects, nuts, and berries each fall. “They eat and eat and eat,” Greenberg says. “Some of these birds almost double their body weight as they deposit fat.”

Researcher Rebecca Holberton removes a blackpoll warbler from a net used to trap these birds for study.

© Rebecca Holberton

Migratory songbirds need to pig out because some species fly up to 5 days in a row without stopping to rest or fuel up. They can cover from 3,000 to 4,000 kilometers (1,900 to 2,500 miles) in a single flight. They cross bodies of water as large as the Gulf of Mexico, or even larger, says Rebecca Holberton, a biologist at the University of Maine.

And unlike seabirds, songbirds can’t land on the water if they get tired. They can’t dive for food. Instead, they pack on the pounds—or, in their case, ounces—and carry their energy stores with them.

“Our migratory songbirds are capable of extraordinary things,” Holberton says. “A lot of them cross the Gulf of Mexico in spring and fall, and that’s a good 20-hour trip.”

Ocean routes

Perhaps the most amazing songbird of all is the blackpoll warbler. In summer, this small black-and-white bird lives in forests stretching from Alaska to Nova Scotia. It spends the winter in the Amazon basin.

A blackpoll warbler, photographed in Alaska, shows its fall colors.

Donna Dewhurst, U.S. Fish and Wildlife Service

As migration time nears, blackpoll warblers congregate in forests throughout New England. They then spend up to a week eating. As a result, they double or nearly triple their body weight before taking to the air. That would be like an average fifth-grade student ballooning from 88 pounds (40 kilograms) to 196 pounds (89 kilograms) in just a few days.

Why do the birds eat so much?

“Blackpoll warblers have evolved a unique migration strategy,” Holberton says. “The shortest route from New England to the Amazon basin, if you look on a globe, is to take off from the northeast United States and go out over the ocean.”

The warblers cover this route in a 3-to-5-day nonstop flight, traveling thousands of miles over open ocean. They eventually use up their fat stores, despite their premigration feasts. So, they turn to other sources of energy, Holberton says.

A blackpoll warbler (right) gets much fatter than other birds, such as the yellow-rumped warbler on the left, that migrate much shorter distances.

© Rebecca Holberton

“The birds actually digest their digestive system, using some of the protein it is made of as another energy source,” she says.

This may sound strange, but it makes sense for the birds. “When you’re flying, you don’t need your gut,” Holberton says. Plus, digesting part of the digestive system makes the birds lighter in weight, which helps them conserve energy.

What happens when the birds complete their trans-Atlantic flight? “They can’t eat for a few hours, or even a day, after they’ve landed,” Holberton says. The birds need this time to regrow the organs that their bodies consumed in flight.

Climate change

While many songbirds migrate long distances over water just twice a year, seabirds such as sooty shearwaters spend up to 90 percent of their lives at sea.

Shearwaters are among the most abundant of all birds, and they cruise the entire Pacific Ocean to find food. But their numbers are falling in both the Northern and Southern Hemispheres.

By studying where these birds feed and fly, scientists hope to figure out the reasons for this decline. Shearwaters may serve as important indicators of what’s happening to ocean life and climate on a global scale.

Going Deeper:

Additional Information

Questions about the Article

Word Find: Bird Migration

Archaeopteryx lived 150 million years ago and had teeth and claws like a dinosaur, but wings and feathers like a bird. Feathers also covered its back legs, and a new report argues that these feathered legs acted like small extra wings.

A fresh look at a fossilized Archaeopteryx has shown that this ancient bird had feathers on its legs that may have helped it fly. The inset shows how the bird may have looked with feathers.

Nick Longrich

Nick Longrich of the University of Calgary started wondering if Archaeopteryx might have used leg feathers for flying after researchers in China found a fossil of a ancient bird that had long flight feathers on both its wings and its legs.

Longrich studied an Archaeopteryx fossil that had been found in 1877. When it was first discovered, it had shown hind feathers. But when the fossil was prepared for display, the feathers had been stripped away to show the bones more clearly.

All was not lost, however. When researchers split a rock in two to reveal a fossil, one side has the bones and the other side has an imprint of the fossil. Usually, scientists look at the fossil, but Longrich decided to look at the imprint. It still showed the feathers.

Could the feathers have helped Archaeopteryx fly? Because the feathers were more like the ones that modern birds use for flying than the ones they use just to keep warm, Longrich concluded that Archaeopteryx could have used them for flying, too. He found that the feathered back legs would have allowed the creature to make tighter turns and fly more slowly that it could have without its feathered legs.

But some other scientists don’t think Archaeopteryx could have spread its legs out like wings. They suggest that the hind-leg feathers were like ones on eagles today, which just keep the birds warm and streamlined.—J. Rehmeyer

Going Deeper:

Rehmeyer, Julie. 2006. Flying with their legs: Hind feathers made primitive bird nimble. Science News 170(Sept. 23):197-198. Available at http://www.sciencenews.org/articles/20060923/fob6.asp .

You can learn more about Archaeopteryx at www.ucmp.berkeley.edu/diapsids/birds/archaeopteryx.html (University of California, Berkeley).

Ramsayer, Kate. 2004. Early birds ready to rumble. Science News for Kids (Oct. 27). Available at http://www.sciencenewsforkids.org/articles/20041027/Note3.asp .

These cricket-stalking flies, known as Ormia ochracea, are about the size of houseflies but have big red eyes and fly at dawn or dusk. The flies pinpoint the source of a cricket chirp, and a female deposits larvae on the unlucky

R. Hoy and G. Haldeman

Only male crickets chirp. They have special parts on their wings that, when scraped against each other, make a noise.

In the 1990s, a certain type of fly began hunting Polynesian field crickets found on Kauai, says Marlene Zuk of the University of California, Riverside.

These flies implant their babies in the bodies of crickets. The larvae use the crickets as food, and the crickets eventually die.

Because male crickets make so much noise, they’re easy to locate and suffer the most. So, within 5 years, the male crickets stopped chirping almost entirely, Zuk says.

By 2003, the cricket population had started increasing again, she reports, but only a few of the males had wings with chirping parts that still worked.

“What surprises me most is that the cricket song went away so fast,” says Ron Hoy of Cornell University, who also studies flies and crickets.

The change is an example of natural selection, which is part of the process of evolution. In this case, chirping was a bad quality for a cricket to have on Kauai, and cricket numbers were dropping.

A gene or two happened to change, or mutate, so that the cricket wing couldn’t chirp anymore. In some places, this change would have doomed the mutated crickets. But on Kauai, faced with deadly flies that could zero in on the sound, the mutated crickets thrived and passed the changes on to their young. Now, these silent crickets are the main type of cricket on the island.

Unfortunately for male crickets, their only way of attracting females is by chirping. For now, the silent males cluster around the few remaining chirpers in order to meet female crickets.—E. Jaffe

Going Deeper:

Milius, Susan. 2006. Crickets on mute: Hush falls as killer fly stalks singers. Science News 170(Sept. 23):197. Available at http://www.sciencenews.org/articles/20060923/fob5.asp .

For more about crickets, see www3.telus.net/~ecade/CricketsintheClassroom/
cricketsintheclassroom.html (Elsa Salazar Cade). William Cade and Elsa Salazar Cade discovered the song-tracking fly in 1975 and were the first to report that the female fly follows cricket chirps to deposit larvae on a male.

You can learn more about the cricket-stalking fly Ormia ochracea and its remarkable hearing at www.utsc.utoronto.ca/~amason/Ormia.htm (University of Toronto), www.npr.org/programs/re/archivesdate/
1999/jul/990712.ormia.html (NPR), and en.wikipedia.org/wiki/Ormia_ochracea (Wikipedia).

Science project idea: What factors affect the rate at which a cricket chirps? Information about raising crickets can be found at hobbyscience.com/bug.html (HobbyScience).

New England’s brilliant fall colors attract many visitors.

National Park Service

“Being in the Northeast during autumn is just about as good as it gets in this country,” says David Lee. He’s a botanist at Florida International University in Miami.

Lee studies leaf color, so he’s biased. But plenty of other people share his admiration. Areas of the United States with especially colorful fall displays attract thousands of leaf peepers.

Even as they “ooh” and “aah,” few people know what makes many plants blush in the autumn. Research has shown that leaves change color when their food-making processes shut off. The chemical chlorophyll, which gives leaves their green color, breaks down. This allows other leaf pigments—yellow and orange—to become visible.

No one knows exactly how global warming will alter forests and affect fall colors.

J. Miller

But “there’s still a lot we don’t know about this,” Lee says.

It isn’t clear, for example, why different species of plants turn different colors. Or why some trees become redder than others, even when they’re standing right next to each other. And no one knows exactly how global warming will alter forests and affect leaf-peeping season.

Food factory

In summer, when a plant is green, its leaves contain the pigment chlorophyll, which absorbs all colors of sunlight except green. We see the reflected green light.

The plant uses the energy it absorbs from the sun to turn carbon dioxide and water into sugars (food) and oxygen (waste). The process is called photosynthesis.

When chlorophyll breaks down, yellow pigments in leaves become visible.

I. Peterson

As days get shorter and colder in the autumn, chlorophyll molecules break down. Leaves quickly lose their green color. Some leaves begin to look yellow or orange because they still contain pigments called carotenoids. One such pigment, carotene, gives carrots their bright-orange color.

But red is special. This brilliant color appears only because the leaves of some plants, including maples, actually produce new pigments, called anthocyanins.

That’s a strange thing for a plant to do without a reason, says Bill Hoch of the University of Wisconsin in Madison. Why? Because it takes a lot of energy to make anthocyanins.

Why red?

To figure out the purpose of the red pigment, Hoch and his coworkers bred mutant plants that can’t make anthocyanins and compared them with plants that do make anthocyanins. They found that plants that can make red pigments continue to absorb nutrients from their leaves long after the mutant plants have stopped.

Red leaves get their color from a pigment called anthocyanin.

I. Peterson

This study and others suggest that anthocyanins work like a sunscreen. When chlorophyll breaks down, a plant’s leaves become vulnerable to the sun’s harsh rays. By turning red, plants protect themselves from sun damage. They can continue to take nutrients out of their dying leaves. These reserves help the plants stay healthy through the winter.

The more anthocyanins a plant produces, the redder its leaves become. This explains why colors vary from year to year, and even from tree to tree. Stressful conditions, such as drought and disease, often make a season redder.

Now, Hoch is breeding plants for a new set of experiments. He wants to find out whether turning red helps plants survive cold weather.

“There’s a clear correlation between environments that get colder in the fall and the amount of red produced,” he says. “Red maples turn bright red in Wisconsin. In Florida, they don’t turn nearly as bright.”

More protection

Elsewhere, scientists are looking at anthocyanins in other ways. A recent study in Greece, for instance, found that as leaves grow redder, insects eat them less. On the basis of this observation, some scientists argue that red pigments defend a plant against bugs.

Leaves may turn red in the autumn to protect themselves from the sun’s ultraviolet rays.

J. Miller

Hoch rejects that theory, but Lee thinks that it might make sense. He points out that red leaves contain less nitrogen than green ones do. “It may actually be that insects avoid red leaves because they’re less nutritious,” Lee says.

However, “it’s pretty confusing at this point,” Lee admits. “People debate back and forth.”

To settle the debate, scientists will need to look at more species under more conditions, Lee says. So, he’s now researching leafy plants rather than trees. He’s especially interested in tropical plants, whose leaves turn red when they’re young rather than old.

You can do your own leafy experiments. Observe the trees in your neighborhood and keep track of weather conditions. When autumn begins, write down when the leaves change, which species change first, and how rich the colors are. You can even see anthocyanins under a simple microscope. After several years, you might start to notice some patterns.

Going Deeper:

Additional Information

Questions about the Article

Word Find: Leaf Color

In this artist’s illustration, a newfound planet closely orbits a star that’s just 450 light-years from Earth. A partner star (top center) lies in the distance. The inset compares Jupiter (left) with the puffy planet, HAT-P-1b (right).

D. Aguilar

The newfound planet is called HAT-P-1b. It’s 450 light-years from Earth and 36 percent wider than Jupiter, which is the largest planet in our solar system.

HAT-P-1b circles its parent star very closely—much more closely than Earth circles its own parent star, the sun. It also has a surprisingly low density. Although it’s bigger than Jupiter, it has only half of Jupiter’s mass. That makes it a puffy giant.

The density of HAT-P-1b is the lowest of any known planet, says codiscoverer Robert Noyes of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

That’s very unusual for a planet, especially one that orbits its star so closely. “We have a bit of a puzzle,” Noyes says.

Astronomers found HAT-P-1b using six small, robotic telescopes. Four of the telescopes are at the Whipple Observatory in Arizona, and the other two are in Hawaii.

They detected the planet because, while orbiting, it passes directly between Earth and its parent star, the fainter member of a double-star system called ADS 16402. Each time it does this, the planet blocks a little bit of the star’s light reaching Earth.

HAT-P-1b is an extrasolar planet, which means it exists outside our solar system. It’s one of about 200 extrasolar planets that astronomers have discovered so far.

Only one other extrasolar planet has a density nearly as low as that of HAT-P-1b. Originally, some astronomers had considered this planet a fluke. Now, they have to take more seriously the idea that puffy, hot supergiants may not be that rare.—E. Jaffe

Going Deeper:

Cowen, Ron. 2006. Oversize orb: Puffy planet poses puzzle. Science News 170(Sept. 16):181. Available at http://www.sciencenews.org/articles/20060916/fob5.asp .

Sohn, Emily. 2006. Pluto and the plutons. Science News for Kids (Aug. 23). Available at http://www.sciencenewsforkids.org/articles/20060823/Note3.asp .

______. 2005. Cousin Earth. Science News for Kids (June 29). Available at http://www.sciencenewsforkids.org/articles/20050629/Note2.asp .

______. 2004. A very distant planet says “cheese.” Science News for Kids (Sept. 22). Available at http://www.sciencenewsforkids.org/articles/20040922/Note2.asp .

______. 2004. Planet hunters nab three more. Science News for Kids (Sept. 8). Available at http://www.sciencenewsforkids.org/articles/20040908/Note2.asp .

______. 2003. A planet’s slim-fast plan. Science News for Kids (March 19). Available at http://www.sciencenewsforkids.org/articles/20030319/Note2.asp .

Road builders uncovered this stone slab, now known as the Cascajal block, in a gravel quarry in Veracruz, Mexico.

Image courtesy of Stephen Houston

Road workers discovered the stone in 1999 while digging in a gravel pit near Veracruz. This area of Mexico was at the center of the ancient Olmec civilization.

Scientists who have studied the rock, known as the Cascajal block, say that it displays an early form of Olmec writing, dating back nearly 3,000 years.

Signs inscribed on this slab from southern Mexico may represent the earliest writing in the Americas.

Image courtesy of Stephen Houston

Scientists had previously found samples of Olmec writing from 2,650 years ago. The new block is older and clearly shows writing, says Stephen D. Houston of Brown University in Providence, R.I.

One side of the stone block is covered with 62 carved signs. Twenty-eight of these signs are distinctive elements, similar to individual letters, that might represent things like corn, eyes, or animal skin. The signs run across the block, just as words run across a page.

This drawing shows the 62 symbols carved into the Cascajal block.

© Science

Scientists aren’t sure exactly what the symbols mean, and they don’t know whether the writing system had any basic rules or grammar.

This type of writing might have spread across southern Mexico, says Houston. Wooden figurines found at other Olmec sites have a few similar signs carved in the backs of their heads.

Some scientists aren’t sure that the stone bears evidence of writing. The signs on the stone, for example, appear to run horizontally, whereas later writing in the region ran vertically.

Houston, however, suspects that other blocks with writing exist in the area. He and his team plan new excavations near the quarry where the original stone was found.—E. Jaffe

Going Deeper:

Bower, Bruce. 2006. Scripted stone: Ancient block may bear Americas’ oldest writing. Science News 170(Sept. 16):179-180. Available at http://www.sciencenews.org/articles/20060916/fob2.asp .

Peterson, Ivars. 2006. From counting to writing? Muse 9(May/June):40. Available at http://www.sciencenewsforkids.org/pages/puzzlezone/muse/muse0506.asp .

Ramsayer, Kate. 2006. Early Maya writing. Science News for Kids (Jan. 25). Available at http://www.sciencenewsforkids.org/articles/20060125/Note3.asp .

Sohn, Emily. 2005. Stone tablet may solve Maya mystery. Science News for Kids (Oct. 12). Available at http://www.sciencenewsforkids.org/articles/20051012/Note2.asp .

LabZone
Maya Math
http://www.sciencenewsforkids.org/articles/20050119/LZActivity.asp

But it’s also possible to find pygmy elephants, enormous rodents, and giant squid. Such surprising size variations have sent scientists scrambling to understand why certain types of animals grow larger or smaller in some places than they do in others.

One place to find animals with unusual sizes is on an island. In such an isolated setting, creatures that are normally small, such as tortoises and rodents, tend to grow unusually large. Creatures that are normally large, such as deer and elephants, become unusually small.

Large animals, such as elephants, may become smaller when isolated on islands. In contrast, relatively small animals, such as shrews, sometimes evolve into larger species.

© 2006 MBARI

The trend is so common that it has a name: the island rule. Scientists know that it happens, but they don’t yet know why.

The deep sea might hold the answer, says Craig McClain, a biologist at the Monterey Bay Aquarium Research Institute in Moss Landing, Calif.

According to McClain’s research, creatures that live thousands of feet below the surface of the ocean are also often noticeably smaller—or larger—than related species that live in shallow waters. A key reason could be food supply, he says.

Snail studies

McClain and his coworkers focused on snails. The scientists identified every snail genus (group of related species) that includes some species that live in shallow water and other species that live in deep water.

The scientists recorded the average body size of each of about 6,000 species of snails. Then, they looked for trends.

They found that snail species that live in the seas undergo the same types of changes as animal species on islands do. Snails that are large in shallow water get smaller in deep water, while snails that are small in shallow water get bigger in deep water.

This photograph shows three medium-size shallow-water snails and three tiny deep-sea snails (upper left).

© 2006 Craig McClain

Scientists have proposed several theories to explain the island rule. For example, large animals might get smaller on islands because there’s less living space. The same area that supports only 5 ordinary-size elephants could allow, say, 20 small elephants to survive.

But there’s no such space crunch in the deep sea. There’s plenty of room.

As a second explanation, scientists have proposed that when on an island, animals have fewer predators than they do on the mainland. As a result, they can get bigger.

In the seas, however, predators appear to be just as active, if not more so, in the ocean depths as in shallow water.

So, the usual explanations for changes in animal size on islands—cramped living space and predators—don’t appear to apply to creatures that live in the sea.

Food supply

To explain both the island rule and the ocean results, McClain focuses on something that all animals need, regardless of their environment: an adequate food supply.

On islands, there’s less room for food than there is on continents. And only a tiny amount of food ever drifts into the dark, cold depths of the ocean.

Large shallow-water snails tend to evolve into smaller species in deep water, while tiny snails often grow larger.

© 2006 MBARI

This food-based theory is unique, McClain says, because it explains both the shrinking of some species and expanding of others.

If food is scarce and you’re small, for example, getting bigger can help you travel farther for food and survive longer without eating. If food is scarce and you’re large, on the other hand, getting smaller can help you survive on less food.

“The thing that trips me out is being able to describe two completely different things simultaneously with one idea,” McClain says. “Science is about trying to keep it simple.”

Island rule

Experts are intrigued by the possibility that the island rule describes more than just islands.

“It extends a pattern way beyond what I initially thought existed,” says Mark Lomolino, a biologist at the State University of New York College of Environmental Science and Forestry in Syracuse. “When I began to study the island rule, I thought it just applied to mammals.”

This giant deep-sea isopod has evolved to a much larger size in deeper water. These isopods are distant relatives of the tiny pill bugs found in many gardens. They are also related to small, shallow-water isopods that live in tide pools.National Oceanic a

National Oceanic and Atmospheric Administration (NOAA)

Not everyone is convinced that food supply tells the whole story, and scientists continue to discuss other explanations.

To provide additional evidence for his own theory, McClain plans to look for similar patterns among squid, octopuses, clams, oysters, and other animals that may be sensitive to the amount of food in the environment.

No matter what McClain finds, he’s sure to have an interested audience. “Scientists look for fundamental rules about how nature is organized,” Lomolino says. “That’s probably why this is so alluring.”

Going Deeper:

Additional Information

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While courting a female in dim red light, a male cockroach forces air through holes in his abdomen to make soft, enticing whistles.

Jérôme Sueur, University of Paris XI-Orsay

The chirps, trills, and squeaks of many insects, including most other kinds of roaches, come from the rubbing of legs or other body parts against each other.

Mammals and birds, on the other hand, use their breath to make noises. Hissing cockroaches are among the few insects that communicate this way, too. You may have seen giant hissing cockroaches in pet stores or at insect zoos.

When threatened by a predator, hissing cockroaches make loud hisses. Researchers have found that some male roaches also make soft, whispery sounds to get the attention of females.

In the new study, researchers from France focused on the songs of a roach species called Elliptorhina chopardi, which are smaller than the giant hissing cockroaches found in pet stores. During the experiment, a male and a female cockroach shared a piece of wood under a dim red light. For 2 hours, the scientists watched and recorded sounds as the male tried to convince the female to mate with him.

The recordings included sounds in the air and vibrations traveling through the wood under the roaches’ feet. No one has yet studied how E. chopardi hears, but some roaches have “ears” on their legs below the knees. So, it’s possible that the creatures can “feel” sounds through the ground.

The scientists divided the recorded sounds into three categories: hisses, noisy whistles with static-like fuzz, and complex, pure whistles.

The pure whistles sometimes sound like two, intertwined voices. In this case, a roach squirts air through the holes in its abdomen so that it plays two songs at once. That’s like having a person with two mouths, each one whistling a different tune.

The results showed that males didn’t mate unless they made their sweet whistling noises. This finding backs up older research, which found that giant hissing cockroaches, which don’t sing, have to make certain sounds to partner up.—E. Sohn

Going Deeper:

Milius, Susan. 2006. Hey, roach babe: Male cockroaches give fancy courting whistles. Science News 170(Sept. 9):165-166. Available at http://www.sciencenews.org/articles/20060909/fob6.asp .

View a colony of giant Madagascar hissing cockroaches at cricket.biol.sc.edu/usc-roach-cam.html (University of South Carolina).

Science project idea: Learn about raising hissing cockroaches for study at www.uky.edu/Ag/Entomology/entfacts/misc/ef014.htm (University of Kentucky).