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w w w. s c i a m . c o m S C I E N T I F I C A M E R I C A N 29

W H A L E S

Sense and SensitivityThe narwhal sports an eight-foot-long spiraled tooth that makes it resemble a unicorn of the sea. Some thought that the whale, typically 13 to 15 feet long, used it to break arctic ice; others theorized that it served as a lance in male jousts. The tooth, in fact, may be a giant sensor for navigating and hunting. Through electron microscopy of two male tusks,

researchers from Harvard University, the Smithsonian Institution, and the Nation-al Institute of Standards and Technology discovered that a single horn possesses some 10 million nerves running from its surface to its core. Instead of infl icting the narwhals with a massive ice cream head-ache, this sensitive tooth appears capable of detecting changes in water tempera-ture, pressure and particle gradients linked with salinity and prey. Their fi nd-ings surfaced last December at the 16th Biennial Conference on the Biology of Marine Mammals in San Diego. —Charles Q. Choi

P H Y S I C S

Nanoparticles Can’t HideDetecting a virus or any nanosize particle usually means fi xing it to a substrate or attach-ing a fl uorescent probe to it. Neither method is practical for detecting particles in real time. Now University of Rochester physicists have assembled a simple system for doing just that. They split a laser beam in two, sending one half to a sample. When the light hit a small particle, it scattered back and recombined with the reserved half of the laser beam, produc-ing a detectable interference pattern only when a moving particle was present. The method works where others do not, the researchers say, because it relies on the light’s amplitude rather than intensity. The amplitude is the square root of intensity, so it decays much less than intensity as particles get smaller. The investigators have so far detected single particles as small as seven nanometers across. Peruse their fi ndings in the January 13 Physical Re-view Letters. —JR Minkel

B I O L O G Y

Where the Bacteria RoamDespite bacteria’s ubiquity, their diversity in the world’s soils is poorly understood. To get a handle on what makes the organisms thrive, Duke University researchers trekked far and wide to collect a few centimeters of dirt from 98 locations across North and South America, then analyzed each sample for genetic variation. To their surprise, the strongest predictor of high diversity was neutral pH. The acidic soil of the Peruvian Amazon, for example, harbored one half to

one third as many species as did the neutral dirt of the arid American Southwest. “There are a lot of variables that didn’t turn out to be very important,” says co-author Robert Jackson, who adds that a more exhaustive search of different habitats might turn up other stimulators of diversity, such as car-bon abundance. The report was published online January 9 by the Proceedings of the National Academy of Sciences USA. —JR Minkel

NOT FOR JABBING: The narwhal’s horn seems to be a sophisticated sensor.

BRIEF POINTS

■ Buddy system: A dwarf galaxy containing hundreds of thousands of stars seems to be merging with the Milky Way. The new companion galaxy lies 30,000 light-years from Earth, toward the constellation Virgo.

Sloan Digital Sky Survey announcement, January 9

■ Patterns of frog extinctions and lethal fungus outbreaks appear to be synchronized. To some scientists, the connection implicates global warming, which stimulates the fungal growth.

Nature, January 12

■ Just hand me the leash and go away: nursing home residents felt much less lonely when they spent time with a dog, rather than with a dog and other people.

Anthrozoos, March

■ Seeing a person who behaved unfairly get an electric shock triggered the empathy areas in women’s brains, but in men the reward centers were activated instead. Men may fi nd pleasure in retribution, although both sexes reported disliking the unfair person.

Nature online, January 18GL

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