Evolutionary biology: Darwinian serenade
Proc. R. Soc. Lond. B doi:10.1098/rsbp.2006.3736 (2006)
A population of Amazonian frogs that woos with calls (Physalaemus petersi, pictured) seems to be splitting into several species as the females' preferences for different types of call diverge, report researchers at the University of Texas in Austin.
W. Chris Funk, now of the United States Geological Survey in Corvallis, Oregon, and his colleagues gathered genetic evidence to support the idea. They found, for example, that gene flow between groups that have a simple call composed of a single whine component (which Funk pronounces “Chu! Chu!”) and groups that have a complex call containing a whine and a squawk (“Chu hanh! Chu hanh!”) is 30 times lower than within these groups.
Speciation by sexual selection, although supported by theory, is hard to catch in action.
Microfluidics: Go with the flow
Lab Chip 6, 1277–1278 (2006)
The controlled flow of liquids in microscopic channels on 'microfluidic' chips could permit chemical analysis of tiny samples as well as more efficient industrial chemical synthesis. But how can the fluid traffic be directed down the right channels?
Microscopic valves and gates are cumbersome, so Nathaniel Robinson and his colleagues at Linköping University in Sweden propose to do away with all moving parts.
They made channels with floors whose wettability can be controlled electrically, using conducting polymers that have different surface properties when electrochemically oxidized or reduced. Water injected into such a system flows preferentially along the oxidized channels (pictured).
Chemistry: Scenting money
Angew. Chem. Int. Edn. Engl. 45, 7006–7009 (2006)
“Money doesn't stink”, the Roman Emperor Vespasian's son allegedly told him. But your hands do smell after handling coins. Surprisingly, the reason for this has only just been determined.
Dietmar Glindemann of Virginia Polytechnic Institute and State University, Blacksburg, and his co-workers have found that the characteristic metallic aroma produced by touching iron and copper isn't intrinsic to the metals at all — it is a type of body odour. These metals rapidly reduce lipid-based compounds at the skin surface to aldehydes and ketones that give the distinctive musty smell we associate with metal. This process might also explain the metallic taste often experienced in drinking water, and the metallic smell of blood.
Astronomy: Missing helium
Science doi:10.1126/science.1133065 (2006)
Low-mass giant stars may have been spewing much less helium-3 into space than was previously thought, a new model suggests. This could explain why cosmic levels of helium-3 are lower than theory predicted.
Helium-3 was produced in the Big Bang and has since been emitted by giant stars, but the amount observed in the universe at large is less than had been expected given theoretical models of these two processes. Now, Peter Eggleton and his colleagues at the Lawrence Livermore National Laboratory in California have seen the fate of the missing helium in a computer model of a red giant star.
The researchers' three-dimensional model revealed a subtle instability that leads to turbulence within the star and a greater rate of helium-3 burning, greatly reducing the amount lost to space. This makes cosmic levels not much higher than those predicted by Big-Bang theorists seem reasonable.
Cell Biology: Housekeeper has two jobs
Neuron 52, 321–333 (2006)
A novel player in the business of helping brain cells to communicate with each other has been discovered by Deborah Nelson at the University of Chicago, Illinois, and her colleagues.
All nerve cells have channels in their membranes that allow ions to pass in and out of the cell. Ion transport through calcium and potassium channels, for example, triggers nerve cells to fire impulses. Chloride channels, on the other hand, were thought to have a 'housekeeping' function, preserving cell volume and maintaining electrical charge.
Nelson's group found that a chloride channel known as ClC-3 amplifies cell-to-cell communication in immature neurons by propagating action potentials. Later, as the neuron matures, its role changes to one that dampens interneuronal signalling.
Medicine: Targeting birth control
Nature Med. doi:10.1038/nm1420 (2006)
In the quest for a male contraceptive, the drug Adjudin initially seemed a promising candidate. But development slowed when researchers found that the dose that inhibited fertility also caused muscle atrophy and liver inflammation in three out of ten male rats.
Now, Chuen-yan Cheng of the Population Council in New York and his colleagues have targeted Adjudin directly to the testes. They did this by coupling it to a recombinant form of a hormone — known as follicle-stimulating hormone — that is important for producing sperm and whose receptor is restricted to the type of cell in the testis known as a Sertoli cell. Targeting the drug allowed them to block fertility in rats using doses of Adjudin a thousand-fold lower than previously recommended. The researchers hypothesize that targeting Adjudin could eliminate its unwanted side effects.
Physics: Cool it
Nature Phys. doi: 10.1038/nphys443 (2006)
For the first time, physicists have cooled a gas by demagnetizing its atoms. This simple cooling technique has previously only been used for solids.
Marco Fattori and his colleagues at the University of Stuttgart in Germany used lasers to trap a magnetically polarized gas containing about a million chromium atoms. When the team ramped down the applied magnetic field, the atoms' magnetic alignments spread into a number of energy levels, absorbing thermal energy in the process. The temperature of the gas dropped from 19 microkelvin to 16.5 microkelvin in 5 seconds.
By using this process to ratchet the temperature lower still, the authors believe they can push the atoms into a quantum state known as a Bose–Einstein condensate.
Biological chemistry: New twist for DNA
J. Am. Chem. Soc. doi:10.1021/ja065606n (2006)
Unnatural DNA bases that fluoresce will pair up with DNA's natural bases to form a double helix, report Eric Kool and his colleagues at Stanford University in California. Strands of such bases could be used to image and sense specific DNA sequences.
The researchers deciphered the stucture of a stretch of 'xDNA' ten bases long in which each of the four natural DNA bases was matched to one of four 'expanded' unnatural bases containing a benzene ring.
The modified DNA structure (pictured right) is similar to the original form, with the bases forming hydrogen-bonded pairs in a right-handed helix. But the molecule's backbones are further apart and the helix turn is slower, with more base pairs per turn, than in natural DNA.
Cell Biology: Dual use
Cell 127, 397–408 (2006)
The protein PGC-1α not only stokes up energy production in mitochondria, but also induces enzymes to detoxify the damaging reactive oxygen species (ROS) that are a by-product of energy production.
This finding, from Bruce Spiegelman of Harvard Medical School in Boston, Massachusetts, and his colleagues, might explain how some tissues, such as muscle, can ramp up mitochondrial activity without suffering self-inflicted damage.
The researchers showed that mice lacking the Pgc-1α gene are abnormally sensitive to ROS damage, and that PGC-1α protects brain cells in culture from ROS damage. They propose that PGC-1α could be a therapeutic target for diseases such as Alzheimer's and Parkinson's, which are associated with mitochondrial dysfunction and ROS damage.
Royal Holloway, University of London, UK
Methane humour hides serious issues, argues a geologist.
Methane people are like the Jumblies of Edward Lear's poem — far and few, far and few. We work together across continents, sharing air samples in 'round robin' experiments. We also suffer bovine eructation jokes; but it's not just about cows' breath.
Methane is a potent greenhouse gas, produced by wetlands, fossil fuels, grass and forest fires, and rice paddies. But there are major puzzles in the global budget. Methanologists at a recent meeting in Cape Town, South Africa, discussed two of these.
One stems from experiments suggesting that plants emit methane (F. Keppler et al. Nature 439, 187–191; 2006). Our first reaction was 'surely not!', yet satellite studies of tropical forests seem to back up the result. We folk who once energetically sampled the atmosphere on mountain peaks are becoming plant biochemists, watching air bubble through flasks.
Another dispute surrounds methane leaks from fossil fuels. We used to estimate leakage by measuring the carbon-14 in methane. But nuclear power stations release this, so the technique became useless.
Recently, researchers reanalysed methane's carbon-14 record in a way that avoids the nuclear problem (K. Lassey et al. Atmos. Chem. Phys. Disc. 6, 5039–5056; 2006). The result is surprising: roughly 29% of atmospheric methane is fossil — much more than expected. Some of this leakage is geological (that's a worrying puzzle too), but most is from gas and coal industries.
Methane is the quickest, cheapest, easiest greenhouse-gas target. But governments aren't interested. Important monitoring programmes were cut recently in Europe and Australia, and UK regulators even limit industry proposals for leak reduction. Are we looking a gift cow in the mouth?