American Scientist

This roundup summarizes some notable recent items about scientific research, selected from news reports compiled in Sigma Xi’s free electronic newsletters.

Swarms of Giant Trilobites

Trilobites roamed the ocean floor for some 300 million years. The largest known examples of these extinct arthropods recently turned up in a Portuguese quarry. Previously, specimens larger than 30 centimeters were rare. But the new cache of thousands of fossils includes individuals that top 80 centimeters in length. What’s more, many of the animals were clustered in groups of a few to more than a thousand, some of them in the act of shedding their exoskeletons. The authors say the clusters prove that trilobites, like today’s horseshoe crabs, gathered in social groups to molt and mate.

Gutiérrez-Marco, J. C., et al. Giant trilobites and trilobite clusters from the Ordovician of Portugal. Geology 37:443–446 (May)

Little Boxes Made of…

DNA origami forces a long circular strand of DNA into a specific shape by mixing it with many shorter “staple” strands. The staple strands entwine with complementary sections of the long strand and pull it into shape. Researchers have used the method to create nanoscale smiley faces, a map of North America—and now, three-dimensional DNA boxes just 30 nanometers across. The 3-D advance used a computer program to predict the sequences of 220 staple strands that would assemble the one long strand into a box. The nanocubes even open up when exposed to a specific DNA “key,” hinting at future applications in drug delivery.

Andersen, E. S., et al. Self-assembly of a nanoscale DNA box with a controllable lid. Nature 459:73-76 (May 7)

Sleepy Genes

People with narcolepsy suffer from uncontrollable daytime drowsiness and sudden bouts of sleep. The condition arises from lack of hypocretin, a wakefulness-promoting hormone produced by just a few brain cells. Narcoleptics share a variant of the gene for an immune system protein, human leukocyte antigen (HLA). Researchers have therefore suspected that an autoimmune disorder kills the hypocretin-producing brain cells, but further evidence has been hard to find. Now a genetic study of nearly 4,000 narcoleptics and healthy controls identifies another narcolepsy-associated variation in an immune-system gene. This one codes for T-cell receptor alpha, a protein that interacts with HLA. Still, not everyone with the mutations has narcolepsy, so the next step is to find what triggers the autoimmune assault.

Hallmayer, J., et al. Narcolepsy is strongly associated with the T-cell receptor alpha locus. Nature Genetics (published online May 3)

Better Bee News

The U.S. and Europe have watched in despair as their honeybee (Apis mellifera) populations decline. Some researchers have predicted a grim global crisis in which crops won’t bear fruit for want of pollinators. But a new analysis of a global database of managed honeybees shows that, despite local losses, global bee numbers have risen 45 percent since 1961. Furthermore, the authors note that it’s luxury crops such as cherries, mangoes and nuts—not staples such as rice and wheat—that require bees. Global demand for luxury crops has escalated out of proportion to total food production, and out of proportion to the bees—leading to a perceived pollinator crisis.

Aizen, M. A., and L. D. Harder. The global stock of domesticated honey bees is growing slower than agricultural demand for pollination. Current Biology (published online May 7)

Effici-ant Decisions

Forget comparison shopping. When rock ants (Temnothorax albipennis) have to find a new home, workers start scouting for a dry dark crevice under a rock. But there’s no need for individual ants to compare different crannies and choose the best. So say researchers who attached tiny radio transmitters to hundreds of the two-millimeter-long workers. The transmitters revealed that most scouts visited only one potential nest site. Ants that found a good-enough nest on the first try stayed there, whereas 40 percent of ants that found a substandard (too bright) nest quickly left it to keep searching. The result: A quorum accumulated at the good-enough nest, and the colony moved in.

Robinson, E. J. H., et al. Do ants make direct comparisons? Proceedings of the Royal Society B: Biological Sciences (published online April 22)

Hunting the Indus Language

When it disappeared some 4,000 years ago, the Indus culture left behind sculptures, carts and the earliest evidence of urbanization on the Indian subcontinent. Whether it also left written records is a matter of debate. Many Indus artifacts are inscribed with pictographs, but it is unclear whether these represented the culture’s spoken language. A new statistical analysis suggests that they did. Researchers analyzed the pattern in which the symbols appeared and found that it was neither random nor completely rigid. Rather, the sequence was most like that of words or characters used to represent known spoken languages. Without another Rosetta Stone, however, the meaning of the symbols remains a mystery.

Rao, R. P. N., et al. Entropic evidence for linguistic structure in the Indus script. Science (published online April 23)

Stop Scratching!

Scratching satisfies an itch. But how it does so is a neurological puzzle. Now researchers have tracked down neurons that are active during itching and also calmed by scratching. Spinal cord cells called spinothalamic tract (STT) neurons receive itch signals from neurons in the skin, and transmit those signals to the brain. To see if scratching could calm the same STT cells, neuroscientists injected the legs of sedated monkeys (Macaca fasciularis) with histamine. The STT neurons went crazy—and scratching the legs slowed the firing in a subset of the cells. Researchers hope to target comparable neurons in humans to stop itching in diseases such as shingles or psoriasis.

Davidson, S., et al. Relief of itch by scratching: State-dependent inhibition of primate spinothalamic tract neurons. Nature Neuroscience 12:544–546 (May)