This month in Science Roundup:
Of the thousands of different metabolites that plants can produce, many of them are released in the form of invisible chemical clouds. These volatile compounds serve a diversity of plant functions from communication to defense, but they also provide aromatic benefits for humans and other animals. In a collection of articles published with the 10 Feb 2006 issue, Science Magazine and its online companion sites explored the complex and fascinating bouquet of plant volatiles. Review and Perspective articles in Science examined the biosynthesis, biochemistry, and evolution of volatile compounds and the ways in which these chemicals contribute to the scents of flowers and fungi and to the distinct flavors of foods and wines. Articles and resources in the Signal Transduction Knowledge Environment highlighted the evolution of olfactory signal transduction, biochemical pathways of the plant hormone jasmonate, and the regulation of plant gene expression by auxin. Meanwhile, the Science of Aging Knowledge Environment looked into the nature of age-related olfactory loss and ScienceCareers.org featured a series of articles on thriving careers in plant science.
Music executives, movie makers, and book publishers in search of the secret recipe for stardom were dealt a scientific blow this month. According to a Report by Salganik et al. ( http://www.sciencemag.org/cgi/content/short/311/5762/854) in the 10 Feb 2006 Science , there are no guarantees when it comes to knowing who or what the next big hit will be. In a study designed to understand the social underpinnings of success, the team of sociologists set up an artificial "music market" -- a Web site where people could listen to, rate, and download previously unknown songs by unknown musicians. Participants in one group were only given song titles and band names as their guide, while other groups received information about previous participants' choices (i.e., how many times songs were downloaded). The researchers found that popular songs were more popular (and unpopular songs less popular) in the groups where participants had access to other people's opinions; but which particular songs became very popular was nearly impossible to predict. Success was also only partly determined by quality: The best songs rarely did poorly, and the worst rarely did well, but any other result was possible. As noted in an accompanying Perspective by P. Hedström ( http://www.sciencemag.org/cgi/content/short/311/5762/786), "the study also makes an important methodological contribution by showing how the Web can be used for conducting large-scale [sociology] experiments."
Sub-Saharan Africa continues to bear the brunt of the HIV epidemic and is home to more than 25 million adults and children living with HIV/AIDS. But there is encouraging news that HIV infection rates are declining in some countries. In a Report in the 3 Feb 2006 Science , Gregson et al. ( http://www.sciencemag.org/cgi/content/short/311/5761/664) showed that in Zimbabwe , the HIV epidemic is slowing down because of a large-scale change in sexual behavior -- particularly among young and educated people. According to the new study, HIV prevalence in eastern Zimbabwe fell from an average of 23% to 20.5% between 1998 and 2003. The decline was most pronounced in men aged 17 to 29 years and in women aged 15 to 24 years and may be due in part to men and women waiting longer to start sexual activity and to fewer sexually experienced individuals engaging in casual sex. National prevention programs, condom use, and increased fear of death from AIDS are also likely contributing factors.
A related Report by Stover et al. ( http://www.sciencemag.org/cgi/content/abstract/1121176v1) published online Science Express on 2 Feb 2006 underscored the importance of sustaining HIV prevention efforts worldwide. Their analysis revealed that implementation of AIDS prevention measures targeting sexual transmission and drug users in low- and middle-income countries could prevent 30 million new infections in the next 10 years. Furthermore, greater spending on prevention now would actually produce a net financial saving as future costs for treatment and care are averted. An accompanying Perspective by R. Hayes and H. Weiss ( http://www.sciencemag.org/cgi/content/short/311/5761/620) in the 3 Feb issue highlighted the two studies.
Apoptosis, or programmed cell death, of certain immune cells is an important means of preventing autoimmunity -- a phenomenon in which the body attacks its own tissues. Immunologists trying to understand the basis of autoimmunity have previously focused one the overactivity of T lymphocytes, which are crucial to fighting infection. Now, a Report by Chen et al. ( http://www.sciencemag.org/cgi/content/short/311/5764/1160) in the 24 Feb 2006 Science shows that correctly regulated cell death of another central immune cell -- the dendritic cell (DC) -- is also required to maintain immune control. DCs are normally important for initiating the immune response by activating lymphocytes. In the study, the team genetically engineered mice to express an enzyme that inhibits apoptosis in their dendritic cells. This resulted not only in the accumulation of DCs, but also in chronic lymphocyte activation. Even more telling was that the mice also developed classic signs of autoimmunity including the production of antinuclear antibodies and antibody deposition in the kidneys. As noted in an accompanying News story by J. Marx ( http://www.sciencemag.org/cgi/content/short/311/5764/1086a), the new finding "points to dendritic cells as possible targets for therapies aimed at treating autoimmune diseases."
Is the primate brain a generalized machine that can tackle a wide range of problems, or is it composed of individual components, each specialized for a specific task? In a Report in the 3 Feb 2006 Science , Tsao et al. ( http://www.sciencemag.org/cgi/content/short/311/5761/670) offered compelling support for the "modular" hypothesis. Using functional magnetic resonance imaging (fMRI), the team first showed that macaque monkeys have three areas in their brains that selectively respond to faces. Next, they targeted electrodes into one of the regions, called the "middle face patch", to record the responses of individual neurons. Amazingly, 97% of the neurons in this area responded exclusively to faces -- and convincingly so. On average, the neurons responded at least twice as strongly to faces as they did to other objects. Some neurons showed weak activity in response to items such as apples, clocks, and other round objects similar in shape to faces. It remains to be seen if any of the face-selective patches in monkeys is homologous to the human brain region associated with face perception. But as noted in an accompanying Perspective by N. Kanwisher ( http://www.sciencemag.org/cgi/content/short/311/5761/617), the new findings "provide the strongest evidence yet for extreme specificity of a cortical region for a complex high-level function."
We generally believe that taking time to think about a decision will result in a good choice. And the more complicated the decision, the more time many of us will spend agonizing over it. Now a Report in the 17 Feb 2006 Science suggests that thinking too much can sometimes get in the way of making the right decision. In a set of laboratory and "real-world" experiments, Dijksterhuis et al. ( http://www.sciencemag.org/cgi/content/short/311/5763/1005) studied people making a range of consumer choices -- from simple ones like deciding what kitchen accessories to buy, to more complex ones like choosing a new car or furniture. They found that shoppers who spent time consciously thinking about simple items like oven mitts or shampoo were generally pleased with their purchases. But when faced with a more complicated choice like picking the best of 4 cars based on 12 attributes (with one car clearly better than the rest) conscious thinkers performed no better than chance, choosing the best car only 25% of the time. Even more surprising was that when researchers distracted the participants with puzzles before asking for their car choices, more than half ended up picking the best car. Counter to what we might think, the findings suggest that as choices become more complex, better decisions come from allowing one's unconscious to sift through the options.
Sexual reproduction is energetically expensive. . . so why bother? It is believed that most organisms have sex because genetic recombination provides a fitness advantage by speeding up the rate of adaptive evolution. That is, deleterious mutations have a better chance of being eliminated (and more quickly) when genetic material is exchanged. Now, a Report by Paland and Lynch ( http://www.sciencemag.org/cgi/content/short/311/5763/990) in the 17 Feb 2006 Science has provided empirical evidence in support of this hypothesis. The team examined different populations of the water flea Daphnia pulex , which can shift from being sexual to being asexual and thus serves as an ideal system for studying the genetic consequences of sexual reproduction. Their analysis shows that the asexual flea lineages developed four times as many mildly deleterious mutations in their mitochondrial genomes as the sexual lineages. An accompanying Perspective by R. Nielsen ( http://www.sciencemag.org/cgi/content/short/311/5763/960) noted that these results support the hypothesis that sexual reproduction plays a prominent role in reducing the mutational burden in populations.
Before the demise of dinosaurs around 65 million years ago, most early mammals were thought to be small, nocturnal, and terrestrial. Now, a new fossil from the Middle Jurassic suggests that some were aquatic. In a Research Article in the 24 Feb 2006 Science , Ji et al. ( http://www.sciencemag.org/cgi/content/short/311/5764/1123) described a large 164-million-year-old fossil unearthed from China that has impressions of fur and a scaly beaverlike tail. The animal was about a half meter in length, and limb and other skeletal features as well as evidence of webbed feet suggest that it was well-adapted for swimming and burrowing. Dental remains are indicative of teeth suited to eating fish and aquatic invertebrates and resemble those of modern carnivorous seals. As noted in an accompanying Perspective by T. Martin ( http://www.sciencemag.org/cgi/content/short/311/5764/1109) the new fossil "is a further jigsaw-puzzle piece in a series of recent discoveries, demonstrating that the diversity and early evolutionary history of mammals were much more complex than perceived less than a decade ago."
The Sahara covers some 9 million square kilometers and is the largest warm-climate desert it the world. Its past has not always been dry, however. Throughout its history, the region has endured a series of wet periods, the last occurring about 6000 years ago. These humid spells have made it difficult to date the onset of the Sahara 's desert condition. Now, a study by Schuster et al. ( http://www.sciencemag.org/cgi/content/short/311/5762/821) in the 10 Feb 2006 Science describes wind-driven dune deposits from the northern Chad Basin , which indicate that at least part of the Sahara had formed by 7 million years ago. Patterns of dune formation and sand ripples indicate the same trade winds that prevail today helped shaped the desert at that time. In one region, sandstones were overlain with a geological layer bearing a number of vertebrate fossils, including Sahelanthropus tchadensis , the earliest known hominid. The researchers contend that the repeated sequences of wind- and water-deposited formations they observed provide strong evidence for arid-humid climate changes. This in turn suggests that desert conditions existed repetitively rather than continuously. These new insights extend the demonstrated age of the onset of desert conditions in the Sahara and may prove useful in paleoclimate models.
Of all the ringed planets -- which include Jupiter, Saturn, Uranus, and Neptune -- Uranus seemed to have the most straightforward ring system. It was made up of a series of dark, narrow rings and a family of small, inner moons orbiting in the region between the ring system and two large, classical moons. Or so we thought. In a Research Article in the 17 Feb 2006 Science Showalter and Lissauer ( http://www.sciencemag.org/cgi/content/short/311/5763/973) reported the discovery of two more moons, named Mab and Cupid, and two faint, dusty rings. All of them orbit outside of Uranus's main ring system but are interior to the large moons. They were spotted in images from the Hubble Space Telescope and traced in earlier pictures taken by the Voyager 2 spacecraft. The findings yield a picture of a "second ring system" comprising 11 densely packed and dynamically interacting moons, a possible tiny or disrupted moon, and the belts of dust that emerge from them. Orbital simulations further suggest that the whole system may be gravitationally unstable or chaotic. An accompanying Perspective by C. D. Murray ( http://www.sciencemag.org/cgi/content/short/311/5763/961) highlighted the discoveries.
Magnetic fields on stars like the Sun affect their interiors, their atmospheres, and their surrounding environment. Understanding the large- and small-scale structure of these fields can help us understand how they formed and what impact they may have on long-term stellar evolution. In the 3 Feb 2006 Science , a Report by Donati et al. ( http://www.sciencemag.org/cgi/content/short/311/5761/633) revealed unexpected details of stellar magnetism and the internal mechanisms of an important class of stars called the "M stars". These cool stars constitute most of our stellar neighbors, but until recently they were too dim to be detected by common diagnostic techniques. The turbulent nature of M stars, as well as their rapid rotation, has made studying their magnetic fields all the more tricky. In the new study, the team used Doppler imaging to reconstruct a 2-dimensional map of the surface of a star known as V374 Peg from a series of high-resolution spectral line profiles and other signatures of polarized light. Their observations show that in contrast to existing theoretical models, the magnetic field of this very-low-mass star is strong and dipolar despite vigorous convection (movement of energy from the star's core to the surface). An accompanying Perspective by G. Basri ( http://www.sciencemag.org/cgi/content/short/311/5761/618) highlighted the Report.
Quantum computing holds great promise for solving difficult problems that would take classical computers an infinitely long time. But working out the algorithms to solve these problems efficiently remains a major hurdle. According to a Report in the 24 Feb 2006 Science , help lies in the realm of geometry. In essence, a quantum computer designer wants to figure out the shortest path from the input data of a problem to its output solution without having the number of calculations grow out of hand along the way. Using that logic, Nielsen et al. ( http://www.sciencemag.org/cgi/content/short/311/5764/1133) showed that finding optimal quantum circuits is essentially equivalent to finding the shortest path between two points in a certain curved geometry -- a geodesic, which also represents a path that a freely falling object would take. In making this analogy, the researchers open up the possibility of using the mathematical tools of Riemannian geometry (which involves the study of curved surfaces and spaces) to suggest new and efficient quantum algorithms or to reveal limitations of the power of quantum computers. An accompanying Perspective by J. Oppenheim ( http://www.sciencemag.org/cgi/content/short/311/5764/1106) highlighted the study.