Honey's sweet smell attracts more flies than does vinegar's sour odor, but the ultimate fruit-fly magnet is eau de nothing.
Ditching pheromones makes male and female fruit flies super-sexy to male flies, even to males of other species, Joel Levine, a neurogeneticist at the University of Toronto at Mississauga, and his colleagues report in the October 15 Nature. The discovery suggests pheromones can be back-off rather than come-hither signals. The finding could lead to a better understanding of the chemical signals that help flies and other animals interpret the world, including how to select a mate and how to distinguish other species.
"It's a very careful paper," says Nicolas Gompel, a neurogeneticist at the Developmental Biology Institute of Marseilles-Luminy in France. "I think it's raising the bar in the field because of the clarity of the analysis."
Typically fruit flies meet each other over rotten fruit. Often several species of fruit flies mill about the same location. Many of the species look very similar,at least to human eyes.
"We geneticists can hardly tell them apart unless we dissect them," Gompel says.
It was a mystery how fruit flies could tell their own species from others. Scientists thought that sight and sound probably played big roles in distinguishing both species and gender. For instance, male fruit flies serenade females during courtship and each species' love song is different. A male fly's "music" and appearance would also probably keep other amorous males from approaching him.
Scientists knew that chemicals called pheromones are important in telling males from females and one species from another, but no one knew how to interpret the message the flies were sending in a mix of 30 or more pheromones.
To decipher the message, Levine and his colleagues used a genetic trick to selectively kill special pheromone-producing cells called oenocytes that are usually part of the flies' abdomens. The team essentially created scentless flies.
Surprisingly, the lack of a come-hither signal was more of an aphrodisiac for male flies than pheromones were. Normal male flies were more attracted to both male and female flies lacking pheromones than to normal females. Males from three other Drosophila species also courted scentless D. melanogaster females, something they would not do in the wild.
The team could then use the scentless flies as a Rosetta stone to help translate the specific messages sent by different pheromones. Adding back a female pheromone thought to be an aphrodisiac, (7Z,11Z)-heptacosadiene or 7,11 HD, to scentless flies didn't make them any more attractive if worn alone. A male pheromone called cis-vaccenyl acetate or cVA, which male flies pass to females in ejaculate to warn other males away, made both normal and scentless females unattractive to males.
But if the perfume blend contained both cVA and 7,11 HD, the female chemical could "counter the chemical chastity belt imposed by cVA," Gompel writes in a commentary appearing in the same issue of Nature.
"Males are only after one thing. They want to mate," Levine says. Even in the face of conflicting signals, the males "would rather hedge their bets and go for it," than go without a mate.
In addition to identifying gender, the researchers found that just one pheromone created a barrier to mating between species. Adding 7,11 HD — which is not made by other Drosophila species — to scentless melanogaster females erected the species barrier that had been torn down by removing the oenocytes. "7,11 HD says, 'she's not one of them,'" Levine says.
These findings indicate that the chemical signals outweigh sight and sound in helping a male choose a mating partner, and that female pheromones may also serve as "slow down" or "back off" messages to keep males from getting too amorous, Levine says.
Females are more discriminating. Given a choice, normal female fruit flies chose males that produce pheromones over unscented males. "She will not go for the guy who has no odors," Levine says. That could mean that male pheromones put females in the mood.
"We expected the chemicals would play a role," Levine says. "What we didn't expect was how much you could account for with only the chemicals. … We had no reason to think that the effects we saw would be so strong."
n the absence of pheromones, flies engage in unnatural courtship behavior. In this movie, two males attempt copulation with each other’s heads.
Image: Jean-Christophe Billeter. Video: Jean-Christophe Billeter et al., Nature 2009.
Unlike many human brothers and sisters, plant siblings appear to do their best to get along, sharing resources and avoiding competition.
In a study of more than 3,000 mustard seedlings, scientists discovered that the young plants recognize their siblings — other plants grown from the seeds of the same momma-plant — using chemical cues given off during root growth. And it turns out mustard plants won’t compete with their brethren the way they will with strangers: Instead of rapidly growing roots to suck up as much water and minerals as possible, plants who sensed nearby siblings developed a shallower root system and more intertwined leaves.
“It’s possible that when kin are grown together, they may balance their nutrient uptake and not be greedy,” plant biologist Harsh Bais of the University of Delaware said in a press release. The work will be published in an upcoming issue of Communicative and Integrative Biology.
Two years ago, co-author Susan Dudley of McMaster University in Canada observed a similar pattern in the sea rocket, a common seashore plant that also appears to favor its siblings. But the initial studies of kin recognition have been criticized for failing to control for complicating factors, such as resource depletion caused by competition between the unrelated plants. And until now, the researchers didn’t know how plants managed to identify their kin.
As seedlings grow, their developing root system gives off a variety of chemical signals, and the researchers guessed that these secretions might play a role in sibling recognition. To test their theory, the scientists grew wild Arabidopsis thaliana in a sterile liquid containing root extracts from sibling plants, unrelated plants or their own roots. Because each plant was grown in a highly controlled setup, the researchers could be sure any changes in growth were due to differences in the root extracts.
As shown in the time lapse videos below, the seedlings exposed to root secretions from unrelated plants grew significantly longer and more elaborate root systems than those grown in secretions from their siblings. The top video shows unrelated plants, while the bottom one shows siblings.
However, when the scientists blocked root secretions using a chemical called sodium orthovanadate, the differences disappeared, suggesting that the sibling identification system indeed depends on chemicals released by growing roots.
The researchers say their results may have significant implications for farming and agriculture. Although no one knows for sure how sibling recognition would affect crops grown in large monocultures, some researchers think that decreased competition among plants from identical seeds may make monocultures more susceptible to insects and disease.
However, Bais says that the effect of growing a plant with its siblings is likely to be species-dependent, as initial studies have been contradictory. “There is a possibility that the explanation of the trade-offs is not that simple,” he wrote in an email. “We have found that plants could resist pathogens better when grown with siblings compared to strangers, so I would take this with caution and not stretch it to all the plant species.”
Regardless of how sibling recognition affects agriculture, it may be an important consideration for the home gardener.
“Often we’ll put plants in the ground next to each other and when they don’t do well, we blame the local garden center where we bought them or we attribute their failure to a pathogen,” Bais said in the press release. “But maybe there’s more to it than that.”
Two Chinese scientists have successfully made an artificial black hole. Since you’re still reading this, it’s safe to say that Earth hasn’t been sucked into its vortex.
That’s because a black hole doesn’t technically require a massive, highly concentrated gravitational field that prevents light from escaping, as postulated by Albert Einstein. It just needs to capture light — or, to be more precise, electromagnetic radiation, of which visually perceived light is one form.
The desktop black hole, described in a paper submitted to arXiv on Monday, is made from 60 concentrically arranged layers of circuit board. Each layer is coated in copper and printed with patterns that alternately vibrate or don’t vibrate in response to electromagnetic waves.
Together, the patterns completely absorbed microwave radiation coming from any direction, and converted their energy to heat.
Like a near-black hole designed earlier this year and made from photon-absorbing carbon nanotubes, the material could be used in solar energy panels.
Citation: “An electromagnetic black hole made of metamaterials.” By Qiang Cheng and Tie Jun Cui. arXiv, October 12, 2009.
Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecosystem and planetary tipping points.
Wired’s Terminal Man appears to have passed the ultimate mental health test — 30 days without leaving an airport terminal except by plane — with his sanity completely intact.
Wired Science conducted a highly unscientific study of Brendan Ross’s mental health status (i.e., we gave him several self-administered exams to take before and after the big adventure), and it turns out he’s a pretty stable human being.
Despite enduring a month of constant noise, gross public bathrooms and chronic sleep deprivation, Brendan’s stress score bumped only 11 points, from 3 to 14 out of a possible 168. According to Psychology World, a website that publishes an online version of the stress test, his second score still puts him well below the reported national average of 50.
Similarly, Brendan’s score on a multiple-choice anger test jumped by 50 percent, from 20 to 30 out of a possible 250, but he says he never came close to screaming at a flight attendant or fellow passenger.
“It’s not in my nature to snap and start screaming at somebody, I guess,” wrote Brendan in a follow-up survey. “There were people who rubbed me the wrong way, sure, but it never came to that. Maybe it was because I knew they’d make good material for the blog, like the ‘air marshal’ from my last post.”
There were a few moments when Brendan felt the fatigue and stress getting to him, however. He says the mood of his fellow passengers greatly influenced his stress level, and he’d find himself getting testy among a crowd of stressed-out passengers waiting for a delayed flight. “Regional attitudes made a difference too,” he said. “I was much more irritable in New York than, say, Florida.”
Brendan also found sleep deprivation affecting his brain in some unusual ways. For instance, on the second to last day of his trek, the Long Beach airport staff arranged for him to take a quick tour of the airport fire station, where he got to ride in a fire engine and shoot the water cannon. But when they invited him to slide down a fire pole, Brendan found himself suddenly unable to control a normally manageable fear of heights.
“Normally, it wouldn’t have been a problem, but stepping up to the ledge, in the midst of the fatigue and weariness, the phobia kicked in full strength and I couldn’t do it,” Brendan said. “It was embarrassing — I had to walk back down the stairs. It wasn’t the kind of thing that would’ve happened if I was on a normal sleep schedule, I think.”
Wired Science editor Betsy Mason crossed paths with Brendan in New York City’s JFK airport just days before the end of his odyssey. Though he seemed fairly lucid, the weeks of sleep deprivation had definitely taken a toll on his comprehension speed, and probably a little bit on his self awareness as well, as evidenced by his response to “just look normal” in the photo to the right.
and we’re not sure if the fact that he started talking about doing another terminal tour with Brazil’s Azul Airlines on the day his Jet Blue tour ended is a sign that he came through with ease or a sign that he actually has gone crazy.
Wired’s determined flier says the only time he considered giving up was at the very beginning of his trip, and even then the thought crossed his mind only briefly. “The closest I came to giving up was on the second day,” he wrote, “when I was looking at a month of doing this. I thought, ‘Wow, this may have been a monumentally stupid decision.’”
But Brendan persevered, kindly providing us with a month of blog posts detailing the ins and outs of America’s airports. For a first-hand report of air rage, however, it turns out we’d have to find a more irritable traveler.
Images: 1) Brendan riding in a fire truck at the Long Beach airport fire station. / Brendan Ross. 2) Brendan at JFK. / Betsy Mason, Wired.com
By putting sensors in the brains of mice as they ran through a Quake-derived virtual reality, scientists have found a way to study neurological activity in moving animals.
The setup allows for real-time, almost-real-motion tracking of single neurons. That feat has eluded researchers who have a fuzzy, general understanding of brain systems, but little knowledge of how individual cells actually work. They hope that cell-level details will make sense motion, cognition and other complex mental functions.
“One of the major research areas of neuroscience is the development of techniques to study the brain at cellular resolution,” said Princeton University neuroscientist David Tank, co-author of the study published Wednesday in Nature. “The information of the nervous system is contained in the activity of individual neurons.”
Tank’s team studied hippocampal place neurons, which are activated when an animal is in a particular location in its environment. Ever since hippocampal place neurons were identified 40 years go, scientists have wondered exactly what mechanisms make them fire.
However, the fMRI machines used to study brain activity in humans only measure the average output of millions of neurons at once. Studying individual neurons has been possible in cell cultures, but brains in a dish behave different than real, living brains. Tracking individual neurons in moving animals has been impossible.
“The neurons move back and forth while you’re trying to measure things,” said Tank. “So we developed a way to keep the head fixed in space, but still have mice perform behaviors that are usually studied in mice running through a maze.”
Tank’s team designed an apparatus in which a mouse, its head firmly held in a metal helmet, walks on the surface of a styrofoam ball. The ball is kept aloft by a jet of air, so that it functions like a multi-directional treadmill. Around it are sensors taken from optical computer mice, which read the ball’s movement as the mouse runs.
Those readings were the input for the researchers’ virtual reality software — a modified version of the open-source Quake 2 video game engine, tweaked to project an image on a screen surrounding the mouse. Tank called it “a mini-iMax theater.”
Mice in the study ran through a virtual maze designed in the open-source Quark game editor, but rather than earning points or power-ups, they were rewarded with sips of water from a head-side nozzle.
Into the hippocampus of each mouse the researchers inserted a glass capillary just one micron wide at its tip and filled with salt water. Known as a whole-cell patch recorder, it detects electrical currents as they pulse through individual cells.
“It is difficult to overstate the importance of understanding how the dynamics of electrical activity within single neurons is related to firing patterns among collections of neurons that accompany the performance of complex tasks,” wrote Douglas Nitz, a University of California at San Diego cognitive scientist, in a commentary accompanying the findings.
Scientists have proposed at least a half-dozen models of individual neuron behavior to explain the general firing patterns of hippocampal place neurons, whose general behavior is determined by a creature’s specific spatial location. Tank’s team found that individual neurons fired in staccato bursts of varying intensity, a result that fits one of the proposed models.
Those results are likely of interest only to neuroscientists, and “to be fair, more work is needed to nail this down,” said Tank.
Nitz was less reserved, calling the observations “an exciting result” that “may prove generalizable to other brain structures, in particular the cerebral cortex.” But he too was especially excited by the virtual reality-harnessing methodology.
The findings are “a first payment on the promise of the technique,” and “represent a powerful example of what will be learned in decades to come,” wrote Nitz.
Citations: “Intracellular dynamics of hippocampal place cells during virtual navigation.” By Christopher D. Harvey, Forrest Collman, Daniel A. Dombeck & David W. Tank. Nature, Vol. 461 No. 7266, October 14, 2009.
“The Inside Story on Place Cells.” By Douglas Nitz. Nature, Vol. 461 No. 7266, October 14, 2009.
Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecosystem and planetary tipping points.
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