Samplings—News from Nature

July-August 2008

Carved walrus tusk shows early whalers. Photos by Un’en’en excavation team

For many Arctic peoples, whales have traditionally been an important source of food and of bone for buildings and tools. But capturing such enormous quarry is no easy task—it requires a cooperative effort, multipassenger boats, and substantial weaponry. When did Arctic residents develop the requisite skills and technology? Until now the earliest evidence of whaling came from a 2,000-year-old site in Alaska, but a new finding moves that date back substantially in time.

     A team led by Daniel Odess of the University of Alaska Museum of the North in Fairbanks collaborated with Russian colleagues to excavate a 3,000-year-old site called Un’en’en on the Chukchi Peninsula, Russia’s northeasternmost tip. In addition to worked whalebone and heavy lance blades suitable for hunting large animals, the team unearthed an impressive carved walrus tusk. The tusk bears two scenes of men pursuing whales in multipassenger vessels called umiaks, with lines bearing sealskin floats connecting the vessels to the whales. The carving leaves little room for doubt that the communities were indeed whaling, and not simply scavenging bones from washed-up leviathans.

     Other images on the carving include what appear to be men hunting polar bears with bows and arrows, a man stabbing another in the back, small doglike animals, and tents—a rare snapshot of Arctic life 3,000 years ago. (Presented at the annual meeting of the Society for American Archaeology)

Web Link: University of Alaska Museum of the North

—Lydia Bell

	Gentile Francesco Ficetola collects water samples to identify DNA fragments. Three 15-milliliter samples are sufficient to detect the presence of bullfrogs, an invasive species, in this large pond. Photo by Claude Miaud

It’s easy for small creatures to hide in a pond—what with all the murky water, vegetation, rocks, and logs—so biologists who want to catalog them must do a lot of mucking around. A new technique might make that task a lot easier: just collect half a tablespoon of pond water and examine the DNA therein. Bullfrogs, for starters, shed enough DNA into the water to enable their detection, according to a new study.

     Ecologist Gentile Francesco Ficetola, now at the University of Milano–Bicocca in Italy, and three colleagues studied American bullfrogs (Rana catesbeiana), which have invaded European wetlands and displaced many native amphibians. Ficetola and others had already documented the invaders’ distribution in France by surveying more than 2,500 wetlands. For the present study, Ficetola’s team collected small water samples—just half an ounce each—from ponds known either to harbor bullfrogs or to be free of them. The team found bullfrog DNA in every sample from ponds with the animals, but never in samples from ponds without. What’s more, the amount of detectable bullfrog DNA in a sample signaled whether a pond is teeming or only sparsely populated.

     The free-floating DNA, Ficetola says, probably comes from mucus, feces, urine, or decomposing bodies. The next steps will be to extend the technique to additional species and to determine how long a species’ DNA “calling card” persists after animals have left a pond—or been successfully eradicated. (Biology Letters)

Web Links:

     Laboratoire d’Ecologie Alpine

     Claude Miaud

     Gentile Francesco Ficetola

—Stéphan Reebs

When an animal detects an odor, a flurry of activity ensues inside its sensory cells—whether they’re in a dog’s nose or a moth’s antenna. Those cellular mechanisms are extremely complex and were thought to be universal. New research shows, however, that in a striking departure from the rest of the animal kingdom, insects smell things their own way.

     The classical mechanism works like this: an odor molecule binds to a molecular receptor in the membrane of a sensory cell, which triggers a series of reactions inside the cell, which opens a gate that lets in ions, which sends off a message to the brain. The new research, by Koji Sato and Kazushige Touhara of the University of Tokyo, Leslie B. Vosshall of the Rockefeller University in New York City, and colleagues suggests that insects skip the intermediate steps. Instead, the odor molecule binds directly to the gate to open it.

     It’s not clear what, if any, advantage the insects’ unique system might confer, but a rapid response to odors is one possibility. Among the insects the team tested was a species of mosquito that transmits malaria. The skeeters sniff out their victims; the new study may help find ways to block their sense of smell, and thus prevent the spread of disease. (Nature)

—S.R.

Photomicrograph of a soil bacterium growing on the blockbuster antibiotic Levofloxacin as the sole carbon source. Image by G. Dantas and M.O.A. Sommer

That so many bacteria have become drug-resistant is testimony to the microbes’ toughness, but here’s tougher: some bacteria actually eat antibiotics for breakfast. What’s more, such super-tough bacteria are naturally widespread in the soil, according to a new study by Gautam Dantas, graduate student Morten O.A. Sommer, and two colleagues, all at Harvard Medical School.

     To study bacteria with varying degrees of prior exposure to artificial antibiotics, the team sampled dirt from eleven disparate locations, including pristine wilderness, farms, and cities. Then they exposed the samples to eighteen antibiotics, including natural ones like penicillin and synthetics like ciprofloxacin. All eleven soil types sheltered bacteria that could grow on antibiotics—including commonly prescribed ones—as their only source of carbon. What’s more, all but one of the antibiotics became fodder for bacteria in most soil types.

     To be able to eat antibiotics, those bacteria must obviously have a high degree of resistance. Indeed, they tolerate antibiotics at levels fifty times more concentrated than do bacteria that are just conventionally resistant. The poison-munching bacteria aren’t harmful to people, but some of them have close relatives that are, such as the agent of infection, Pseudomonas aeruginosa. Because bacteria swap genes freely, Dantas and Sommer warn that the soil dwellers might be able to transfer the genes for super-resistance to their infective cousins. (Science)

—S.R.

The space surrounding a black hole at a galaxy’s center normally radiates lots of X-rays, yet the vicinity of the black hole called Sagittarius A that lies at the hub of our own Milky Way is unusually dim. It wasn’t always so: 300 years ago, astronomers now say, Sagittarius A flared up with X-rays, blazing out a million times more radiation than it does today.

     How were the astronomers able to peer back in time? Apparently, through a clever trick with mirrors. Next to the black hole, at a distance of 300 light-years, is a cloud of gas and dust that reflects X-rays. Because radiation takes 300 years longer to travel from black hole to cloud to Earth than directly from black hole to Earth, the cloud now shows black-hole radiation as it would have appeared 300 years ago, say Tatsuya Inui and three colleagues, all from Kyoto University in Japan.

     Another possibility is that the cloud emits its own X-rays as charged particles collide with it—but then the emissions would remain constant from year to year. By combining years of observations from several X-ray telescopes, Inui’s team discovered a steep drop in radiation coming from the cloud over a ten-year period. Such instability is a sign of Sagittarius A’s waning X-ray flare.

     Magic tricks aside, the black hole still holds mystery. Nobody knows why it’s quiescent now—or whether it will spring to life again someday. (Publications of the Astronomical Society of Japan)

—S.R.

	World map of newly discovered oceanic currents (rectangles outline two study areas). Oleg Melnichenko (IPRC/UH)

Sailors and scientists have been mapping ocean currents for centuries, but it turns out they’ve missed something big. How big? The entire ocean is striped with 100-mile-wide bands of slow-moving water that extend right down to the seafloor, according to a recent study.

     Nikolai A. Maximenko of the University of Hawaii at Manoa and colleagues developed a precise new method for measuring the topography of the ocean surface by combining data from satellites and from the movements of more than 10,000 drifting oceanographic buoys. In doing so, the team generated detailed maps, in which they first noticed the peculiar striations. Some scientists initially dismissed the stripes as statistical artifacts, but Maximenko’s team dug deeper, looking for a similar pattern in water temperature measurements from two test areas in the Pacific.

     Indeed, though barely detectable, the striated currents are real. They flow past each other in opposing directions at 130 feet per hour—just one-tenth to one-hundredth the speed of major ocean currents—and subtle changes in temperature demarcate their boundaries.

     Maximenko says a new computer model has corroborated some features of the observed striations, but his team is still mystified by their orientation, location, and strength. The discovery is important, he says, because even weak currents can have large effects on global climate and on the flow of food and creatures in the oceans. (Geophysical Research Letters)

Web link: Detailed Data

—Brendan Borrell

Brain Freeze

No one likes making mistakes on the job, but it’s easy to lose focus when you’re stuck doing the same thing over and over. What if you could predict—and prevent—such errors? A new study shows that the brain begins to wander as long as thirty seconds before the body makes an error, a departure signaled by changes in the brain’s blood-flow patterns.

     Tom Eichele of the University of Bergen in Norway, Stefan Debener of the Institute of Hearing Research in Southampton, England, and several colleagues used functional magnetic resonance imaging (fMRI) to monitor the brains of thirteen subjects as they undertook the “flanker task.” In that classic psychological test, subjects select one of two buttons depending on the direction of arrows displayed on a screen. Analyzing the brain’s blood-flow patterns, the team found that a subject tended to blunder after the brain simultaneously activated a set of regions associated with rest, and reduced activity in a different area associated with staying on task. Intriguingly, the change began up to half a minute before an error occurred, and the brain seemed to refocus after the subject caught the mistake.

     The study challenges a long-standing theory that the brain flubs simple tasks because of fleeting, random errors in neuron firing. With the new information in hand, it may be possible to build a device that warns us when we’re drifting off. (PNAS)

—B.B.

Surface of a rose petal SEM image by Lin Feng

Ah, roses. Their heady fragrance and delicate petals glistening with dew could soften the hardest heart. But take a sharper look at the dewdrops. They bead, rather than spread—and that’s because the material composing the petal surface doesn’t bond well with water. Yet the droplets don’t roll off. What binds them to the petals?

     To find out, a team of chemists led by Lin Feng of Tsinghua University in Beijing peered at the petals with a scanning electron microscope. What they saw was a carpet of minuscule bumps covered with even tinier ridges. To confirm that those structures—and not the chemical makeup of the petals—are what grip the water droplets, Feng’s team made a plastic cast of the petal surface. As with the original petal, water droplets stuck to the cast, even when it was turned upside down.

     It’s the texture, then, that does the trick. Texture is also important in the so-called “lotus effect,” which causes water to bead up and roll off many plants’ leaves and petals, clearing away dust and debris. The difference: on drop-shedding surfaces, the tiny bumps have wax-coated tips and are separated by narrower troughs, so they make less contact with water. Feng thinks that the rose’s waxless “petal effect” might help flowers attract pollinators by holding glistening dewdrops.

     Casts like Feng’s could be cheaply manufactured, should any commercial uses be found for the unusual properties of rose petals. But romantics needn’t worry—even a dozen casts won’t convey love messages like the real thing. (Langmuir)

—S. R.

The Warming Earth

	Red-leafed trees in background photograph of a Canadian forest indicate damage by the mountain pine beetle, inset. Beetle photo by Klaus Bolte, Natural Resources Canada; Aerial view: Natural Resources Canada

Hordes of mountain pine beetles are decimating British Columbian forests. Rising temperatures due to global warming have boosted the beetles’ numbers by increasing their reproductive rate and reducing their winter die-off. Now, in a perverse twist, a new study shows that in a few years, the pests will have turned the once climate-friendly forests into net emitters of carbon dioxide (CO₂).

     Since 2000, the beetles have killed off more than 32 million acres of forest, according to Werner A. Kurz and a team of scientists from the Canadian Forest Service. Kurz and colleagues say the current outbreak is an order of magnitude larger than any previous mountain-pine-beetle explosion, and they predict it will take another twelve years or so to taper off. That’s a lot of dead trees, which release CO₂ as they decompose. Meanwhile, there are fewer healthily growing trees left to absorb the greenhouse gas through photosynthesis.

     Using a computer model, Kurz’s team calculated that by 2020, the beetles will have killed so much forest that their net effect will be the equivalent of five years of CO₂ emissions by all the cars and trucks of Canada.

     Kurz and his team are the first to account for large-scale insect outbreaks in an analysis of forest carbon balances—and to show the positive feedback loop between climate change and insect pests. They’re unlikely to be the last, however, given the risk of more boreal forests falling prey to warmth-loving insects. (Nature)

Web link: National Resources Canada

—S.R.

Copyright © Natural History Magazine, Inc., 2008