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Megan McPhee, an assistant research professor at the University of MontanaÕs Flathead Lake Biological Station, offers this explanation:

There are two general explanations for how a fish species might end up in different lakes separated by great distances.

The first is termed “vicariance” by biogeographers, who study the distribution of organisms. In this case, a species originally occupies a much larger, continuous range. Over long periods, geologic, biological and climatic events cause populations to go extinct in scattered places throughout that range, behind isolated present-day populations. For example, during the late Pliocene and Pleistocene epochs (between two million to 0.5 million years ago), western North America experienced a much wetter climate and giant lakes occupied many basins. When an increasingly arid climate swept into the area, large lakes dried into separate, smaller ones—leaving fish

species isolated.

The second explanation is based on dispersal, or movement of individuals away from the population in which they were born. Sometimes these indi-

viduals spread into new areas previously unoccupied by members of their species. In fish, where most species require male-female sex to reproduce, a minimum of one of each sex would be needed to colonize a new lake. Whereas the chance of this event happening once is quite small, in time enough opportunities will arise for these rare dispersals to result in the colonization of new lakes.

Over longer periods, dispersal is often facilitated by headwater capture—a river tributary erodes through

tween two rivers, thus linking them. Although nism is primarily responsible for the transfer dwelling fish, it can also move lake fish between they spend part of their life cycle in rivers.

Finally, humans are responsible for moving great distances. In many cases, this dispersal oc curs intentionally because people want to fish for a particular species outside its native range. In the late 19th century the U.S. Fish Commission made concerted efforts to introduce carp—as a food fish—into the waters of the western U.S., where they can now be found in

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lakes and reservoirs throughout the region. Unsanctioned or even accidental transfer occurs when people release aquarium fish or empty out bait buckets into wild habitats. We have learned that nonnative fish (including carp) often prey on or compete with native species, so such practices are now largely discouraged.

How does Bluetooth work?

Bluetooth Special Interest Group executive director Michael Foley transmits an answer:

Bluetooth is a short-range wireless communications technology that replaces the cables connecting electronic devices. It uses the principles of device “inquiry” and “inquiry scan.” Scanning devices listen in on known radio frequencies for devices that are actively inquiring. When the scanner receives an inquiry, it sends a response with the information needed to forge a connection.

A group of devices then forms a so-called piconet, which may contain one master and up to seven active slaves, with additional slaves that are not currently participating in the network. (A given device may be part of more than one piconet, either as a master or as a slave.) In a piconet, the devices are synchronized to a common clock and frequency-hopping pattern, and they share a radio channel. The pattern, which the master device determines algorithmically, helps to combat interference and fading. The basic hopping pattern cycles through the 79 available frequencies, but it may be adapted to exclude those that are used by interfering devices, improving Bluetooth’s coexistence with static (nonhopping) systems, such as Wi-Fi networks, that may

be in the vicinity of a piconet.

wireless link is subdivided into time units as slots. Bluetooth-enabled devices transin so-called packets during these slots, frequency hopping taking place between transmission and reception of packets. All complexity, of course, goes on without user being aware of anything more than task he or she is trying to complete, such talking hands-free on a cell phone or listenmusic on wireless headphones. ■

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Soaps, household cleaners, sponges, and even mattresses and lip glosses now pack bacteria-killing ingredients. Does adding those ingredients make sense?

Traditionally people wash bacteria from their bodies and homes using soap and hot water, alcohol, chlorine bleach or hydrogen peroxide. Soap works by loosening and lifting dirt, oil and microbes from surfaces so that they can be easily rinsed away with water. General cleaners such as alcohol infl ict sweeping damage to cells by demolishing key struc-

tures, after which the cleaners evaporate. Products containing antibacterial agents, in contrast, leave surface residues, notes Stuart Levy of the Tufts University School of Medicine.

Spurring Evolution

This persistence is problematic. When a bacterial population that survives the first hit of an antibacterial agent vies with the lingering chemical, a small subpopulation armed with special defense mechanisms can evolve. This group then multiplies as its weaker relatives perish, and it will withstand attack the next time the chemical is applied. “What doesn’t kill you makes you stronger” is the governing maxim here; antibacterial chemicals select for bacteria that can endure their presence.

Resistance to topical chemicals is not the only risk. When bacteria become tolerant to these compounds, they sometimes also become less sensitive to certain antibiotic medicines. This phenomenon, called cross-resistance, has already been demonstrated with triclosan, one of the most common chemicals in antibacterial products.

Genetic mutations can arise in bacteria exposed to triclosan for long periods and endow certain types of bugs with resistance to isoniazid, an antibiotic used for treating tuberculosis, explains Allison Aiello of the University of Michigan School of Public Health. Other mutations can allow microbes to supercharge their efflux pumps—protein machines in the cell membrane that can spit out several types of antibiotics, including ciprofloxacin, used to treat anthrax. These effects have been demonstrated only in the laboratory, not in households and other real-world environments, but Aiello suspects that the few household studies conducted so far might

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not have been long enough. “The potential is there,” she says. Scientists have further concerns about antibacterial compounds. Both triclosan and its close chemical relative triclocarban are present in 60 percent of U.S. streams and rivers, points out Rolf Halden of the Johns Hopkins Bloomberg School of Pub-

lic Health.

Both chemicals also end up in the sludge produced by wastewater treatment plants, which is used as fertilizer for crops, opening a potential pathway for contamination of Halden says. “The concentrations in agricultural are very high,” and this abundance, “along with the of pathogens from sewage, could be a recipe for

breeding antimicrobial resistance” in the environment, he adds.

Triclosan has also been found in human breast milk, though not in concentrations considered dangerous to babies, as well as in human blood plasma. There is no evidence that current concentrations of triclosan in the human body are harmful, but recent studies suggest that it compromises the function of the hormone systems in bullfrogs and rats.

No Benefit

Ultimately, the value of such antibacterial additives is questionable. An expert panel convened by the U.S.

Food and Drug Administration determined that there is insufficient evidence for any benefit from consumer products containing them. “What is this stuff doing in households when we have soaps?” asks John Gustafson of New Mexico State University.

Some scientists argue that consumer use of antibacterial products is appropriate in the homes of people with weakened immune systems. In general, however, good hygiene means using regular soaps rather than antibacterial ones, experts say. “The main way to keep from getting sick,” Gustafson says, “is to wash your hands three times a day, and don’t touch mucous membranes.” ■

Coco Ballantyne is a freelance writer based in New York City.

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