S C I E N C E N E W S

When the researchers offered whiffs ofthese substances to the wasps, only a fewrelated compounds inspired males tostart attempting to mate. One chemical,9-hydroxydecanoic acid, had been previ-ously described only in honeybees.

The scientists next set out pairs of deadfemales, one with the scent from a flowerblown over it and the other with the scentfrom a real female wasp. Males respondedto the floral scent with more than twice asmany attempts to mate as they did to thetrue sex lure.

This orchid’s chemical seduction takes theopposite strategy from that of a species inthe same genus that the team had analyzedearlier (SN: 7/3/99, p. 11). That study hadfound that Ophrys spegodes relies on a spe-cific blend of more than a dozen commonchemicals rather than a mix of a few rarecompounds. Finding sister species that takesuch different approaches indicates that “the[orchid] system is very flexible,” Schiestl says.

Says pollination biologist Elizabeth Elleof Simon Fraser University in Burnaby,British Columbia: “Think of it as an armsrace. At the moment, the plants areahead.” —S. MILIUS

Shark SenseGel helps animals detectthermal fluctuations

Sharks possess uncanny skill at trackingdown prey, but it’s unclear how the animalssense their surroundings so acutely. Newstudies suggest that a clear jelly under ashark’s skin keeps the animal informed aboutminute changes in seawater temperature thatmay serve as signposts to feeding grounds.

Brandon R. Brown, a physicist at the Uni-versity of San Francisco, set out to charac-terize this mysterious gel. The salty brew ofglycoproteins fills hundreds of electrosen-sory canals, called ampullae, that connectskin pores to subsurface nerve cells insharks, skates, and rays.

After collecting gel from black-tip reefsharks and white sharks that had recentlydied at aquariums, Brown placed each sam-ple in a tube and warmed one end. He thenmeasured any voltage produced by the tem-perature difference along the gel’s length. Tohis surprise, Brown found that a variation assmall as 1°C would produce a voltage as largeas 300 microvolts. From these data, reportedin the Jan. 30 Nature, he concluded that a

temperature change in seawater of less thana thousandth of a degree Celsius wouldinduce a voltage in the gel filling the ampul-lae large enough for the shark to detect.

Brown wondered why a shark wouldrequire such exquisitely fine temperaturedetection. Sensitivity to one-thousandth ofa degree could be a distraction to the ani-mal unless it served a purpose, he says.

Scientists have known for years thatsharks can home in on prey that congre-gate at thermal boundaries, where theocean’s temperature varies by a coupledegrees over a kilometer or so. Brown con-jectured that sharks use their supersensitivegel to detect these subtle boundaries.

“My guess is that sensing temperature isa pretty good strategy for finding food,”agrees David W. Sims of the Marine Bio-logical Association in Plymouth, England,who has studied sharks and their prey atthermal boundaries. Sharks may use theseboundaries as “foraging corridors,” he says.

Over the years, researchers have pro-posed that sharks use their ampullae to findtheir way and that the sensory canals playa role in detecting temperature. However,the questions of how and how well thecanals might do so haven’t been answeredentirely, Sims notes.

Now, Brown’s work indicates that“sharks seem to have the equipment todetect very small temperature changes,”says Sims. —J. GORMAN

Rackets andRadicalsNoise may cause genedamage in heart

Exposure to loud, continuous sound canpepper free radicals throughout heart tis-sue and cause injury to cells’ DNA that per-

sists after the din subsides. This new find-ing from animal research adds to evidencethat too much noise may be bad for theheart, but some scientists suggest that thechanges may be no more than part of thebody’s general response to stress.

Research over the past 2 decades has sug-gested that in addition to causing hearingloss, excessive noise exposure contributes tohigh blood pressure (SN: 3/28/81, p. 198)and elevated death rates from diseases ofthe heart and arteries (SN: 5/7/83, p. 294).Researchers at the University of Pisa in Italyand elsewhere recently reported that noiseexposure can damage cells’ power-gener-ating structures, or mitochondria.

According to Pisa geneticist Giada Fren-zilli, loud sound sensed by the auditory sys-tem can trigger a surge in blood concen-trations of the hormone norepinephrine,which stimulates heart cells to absorb toomuch calcium. That can weaken the mem-branes of the mitochondria and cause themto release free radicals.

To investigate whether free-radical activ-ity induced by noise might damage DNAin cells’ nuclei, Frenzilli and her colleaguesblasted 10 male lab rats with white noise at100 decibels, a volume heard in some danceclubs and loud industrial workplaces.Meanwhile, the scientists kept a similargroup of rats in relative quiet.

Immediately after 12 hours of these reg-imens, the researchers removed heart cellsfrom half the rats in each group. The remain-ing animals got another 24 hours of quietbefore Frenzilli’s team analyzed their cells.

Under microscopes, mitochondria fromthe noise-blasted rats had more brokenmembranes than did those from animalsthat had experienced quieter conditions.Mitochondria from rats given a day to recoverfrom the din were no better off than thosefrom the other animals exposed to loud noise.

The researchers then examined DNA inthe cells’ nuclei. Again, the sound-exposedanimals displayed damage not suffered by

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SCIENCENEWSThis Week

SENSITIVE GUY Sharks rely on gel under their skin to detect ocean temperatures.

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