Ecology: Chain of death
Loss of a species can spark a cascade of secondary extinctions as the community adapts to its absence. To determine the impact of such secondary extinctions on biodiversity, Owen Petchey of the University of Sheffield, UK, and his colleagues used computer models of food webs and field data.
The impact of secondary extinctions on reducing the diversity of feeding habits in a community turned out to be larger than expected from chance. Secondary extinctions were also more common among species with rather unique feeding habits.
Such correlations could be used to identify high-risk species whose extinction would trigger large losses of biodiversity.
Chemistry: Pole-dancing pumpkins
A molecular valve that is triggered by changes in pH and works in a watery environment like that in the human body has been developed by Jeffrey Zink and his colleagues at the University of California, Los Angeles. The valves are on porous silica nanospheres studded with pole-like molecules. Each 'pole' is threaded with a large pumpkin-shaped molecule of cucurbituril. At neutral pH, the cucurbiturils sit at the bottom of their poles, blocking the pores. As the pH increases, they move up the poles, unblocking the pores and releasing the contents of the sphere, which could be a small-molecule drug. With tweaks, the system could respond to very small differences in pH such as those between healthy and diseased cells.
Evolution: Royal machinations
Ant societies seem to be models of cooperation; queens monopolize reproduction and are maintained by sterile female workers. But William Hughes and Jacobus Boomsma at the University of Copenhagen, Denmark, have found a few cheaters among the leaf-cutter ants (Acromyrmex echinatior).
They found that a queen's offspring by certain males were much more likely to develop into queens themselves — hogging the reproductive opportunities. Cheats make up no more than 20% of the male lines. Evolutionary theory says cheaters must be rare in order to prosper or cooperators will be selected to suppress them.
Marine Ecology: Defensive cloning
Larvae of the sand dollar (Dendraster excentricus) clone themselves as a defence mechanism when they detect the presence of predatory fish.
Dawn Vaughn and Richard Strathmann at the University of Washington in Seattle exposed 4-day-old sand dollar larvae to mucus from fish. Within 24 hours the larvae had formed clones by budding and fission. The clones are smaller than the original larva (clone pictured with an egg for comparison), which probably helps them avoid being eaten.
Until now, cloning was not considered a defensive strategy. Echinoderm larvae were only known to clone themselves in response to abundant food or temperatures favourable to growth and reproduction.
Astronomy: Good samarium
Rare-earth elements spotted by astronomers are helping pin down how distant stars burn.
'Heavy' elements — anything heavier than iron — can be created through one of two fusion pathways. To find out which process rules where, astronomers led by Ian Roederer at the University of Texas at Austin collected spectra from two stars suspected of using different pathways, and scrutinized the elements europium, samarium and neodymium. The team was able to count the fraction of isotopes of each element, concluding that one process dominated in one star and the alternative in the other star.
While not surprising, the finding happily suggests that scientists' understanding of nucleosynthesis “is not wildly mistaken”, the authors write.
Animal Behaviour: Coming out of their shells
Mark Briffa and colleagues at the University of Plymouth, UK, have detected the first signs of personality among crustaceans.
Briffa's team devised a new statistical method to differentiate between natural variability in responses of individual European hermit crabs (Pagurus bernhardus, pictured) to different situations, and a consistent trend in responses that reflects a 'personality'.
P. bernhardus retreats into its commandeered shell at any sign of danger. The team timed how long crabs took to re-emerge from their shells in a variety of situations. Some bold crabs consistently emerged sooner than others.
Nanotechnology: Cells on a roll
Sorting cells in the lab generally means labelling them with chemicals and using expensive cell-sorting equipment. Robert Langer and collaborators at the Massachusetts Institute of Technology have instead capitalized on the natural proclivity of some cells to roll along surfaces, including the insides of blood vessels, to sort them. On coating part of a flow chamber with a ligand called P-selectin, Langer and his colleagues found that cells with the right receptors rolled with the flow until they reached the edge of the coating. The cells then continued to roll along this edge, diverting from the direction of flow at angles of up to 8.6°.
Ecology: Egregious edge effects
How wide is a forest edge? For a fifth of the beetle species found in New Zealand, 'edge effects' — the suite of differences that characterize the fringes of a forest fragment, including increased light and wind — influence the abundance of species more than 250 metres inside the boundary of the forest.
Robert Ewers of Imperial College London and Raphael Didham of the University of Canterbury, Christchurch, New Zealand, also found that edge effects penetrated a full kilometre into the forest for one in eight of a number of common beetle species, a much greater distance than previously reported for invertebrates.
Chemistry: Cobalt coupling
Chemists have found a new way to carry out the most basic, but often the most challenging, of chemical reactions — making carbon–carbon bonds. Robert Bergman and his colleagues at the University of California, Berkeley, have developed a nitrogen-containing cobalt reaction system that makes otherwise docile carbon–hydrogen bonds reactive. Cobalt-containing molecules are first reacted with nitric oxide. The resulting complex holds on to a target molecule — a simple alkene with a carbon–hydrogen bond — while this reacts with another similar alkene. The two molecules become joined by a brand new carbon–carbon bond. Chemists trying to make complex drug molecules now have another trick to try.
Star walks into a bar
Spiral galaxies with star-dense 'bars' in their centre are commonplace in the present-day Universe, but were not in the past.
Kartik Sheth at the California Institute of Technology in Pasadena and his colleagues studied over 2,000 spiral galaxies from different cosmic epochs imaged by the Hubble Space Telescope.
The survey shows that bar galaxies make up roughly 65% of spiral galaxies formed in the very recent past, but were only a third as common when the Universe was half its present age. The bars are frequently found in lower-mass galaxies, whose stars form later on average than those in higher-mass systems.