American Scientist

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

Grapes Need Sex

Wine and table grapes (Vitis vinifera vinifera) haven’t had much recombination in the past 7,000 years. To keep specific flavors and traits together, farmers have grown grapes from cuttings for millenia. That clonal reproduction maintains genetic diversity but does not shuffle it. In an analysis of 950 grape samples from the U.S. Department of Agriculture collection, more than half the accessions were clones of others: Seventeen different pinots, for example, were all twins save for a few mutations. Encouraging some grape sex might let growers incorporate traits for pest resistance from rare and wild varieties. Using modern genetic markers, farmers could still track the flavors and colors required for flawless wine.

Myles, S., et al. Genetic structure and domestication history of the grape. Proceedings of the National Academy of Sciences 108:3530–3535 (March 1)

Methane Monsoon

On Saturn’s moon Titan, the poles are dotted with hydrocarbon seas but the tropics are an arid expanse of dunes and channels. According to new images from the Cassini spacecraft, that desert may be seasonally quenched with methane rain. In late September 2010, an expansive cloud system crossed Titan’s equator and left behind a long dark stain on 500,000 square kilometers of the moon’s surface. Researchers think the discolored ground was wet or flooded, and began to drain or evaporate within a month. If the spring rains continue, they may help explain Titan’s desert stream beds.

Turtle, E. P., et al. Rapid and extensive surface changes near Titan’s equator: Evidence of April showers. Science, 331:1414–1417 (March 18)

Mix and Match Genes

Bacteria and archaea have two ways of gaining new metabolic abilities: Extra copies of their own genes can evolve novel functions, and they can acquire genes from other species. Biologists thought the first method—predominant in eukaryotes—was also the most important in prokaryotes. But a new study of 110 genomes in eight microbial lineages suggests the reverse. When those organisms gained new versions of genes, they did it by acquisition 88 percent of the time. That’s probably because copies of existing genes may be deleted as excess baggage before they evolve useful mutations. New genes from another species, however, can serve a novel function right away.

Treangen, T. J. and E. P. C. Rocha. Horizontal transfer, not duplication, drives the expansion of protein families in prokaryotes. PLoS Genetics 7: e1001284 (January 27)

Shivering in Europe

Early humans lived in Europe for 700,000 long cold years before they mastered fire. That conclusion comes as a surprise to many archaeologists, who thought that controlled flames must have been a prerequisite for human migration into colder climates. But a review of data from more than 100 archaeological sites across Europe revealed no evidence of habitual fire use until 400,000 years ago. After that, remains of ancient hearths and scorched tools appeared with increasing frequency. The authors suggest that the first humans in cold climates must have relied on high metabolism—stoked with lots of protein and an active lifestyle—to weather frosty boreal winters.

Roebroeks, W., and P. Villa. On the earliest evidence for habitual use of fire in Europe. Proceedings of the National Academy of Sciences (published online March 14)

Fire-Ant Headquarters

In the 1930s, fire ants (Solenopsis invicta) from Argentina set up shop in Alabama and spread quickly through the southern United States. Now, the insects’ new home serves as a launch pad for more invasions around the globe. An analysis of fire-ant DNA from 2,144 colonies indicated that California, China, Taiwan and Australia experienced eight distinct introductions from the southern U.S. A ninth ant envoy passed through California before continuing to Taiwan. Researchers aren’t sure why the U.S. fire ants are such super-invaders, but the same traits that helped the first populations settle in the South may give them an edge elsewhere too.

Ascunce, M. S., et al. Global invasion history of the fire ant Solenopsis invicta. Science 331:1066–1068 (February 25)

Amoebas Save Seed

Even single-celled organisms can farm. Social amoebas (Dictyostelium discoideum) live alone and prey upon bacteria until food becomes scarce. Then they form a sluglike collective and creep away together to release spores. Working with 35 strains of wild D. discoideum, researchers discovered that about one-third of the strains always took uneaten bacteria with them when they crawled off. The bacteria then dispersed along with spores, seeding new habitat with good food. That gave the farming strains an advantage when their spores landed on sterile media or on soil with inedible bacteria. But where food was already abundant, the nonfarmers reproduced faster. A patchy food landscape probably maintains the balance between farming and nonfarming strains in nature.

Brock, D. A., et al. Primitive agriculture in a social amoeba. Nature 469:393–396 (January 20)

Bird-Inspired Design

Woodpecker anatomy has inspired a new shock absorber for delicate electronics in plane crashes and bombings. The birds incessantly slam their heads against hard surfaces without brain damage. So engineers studied X-ray scans of a golden-fronted woodpecker (Melanerpes albifrons) and modeled its shock-absorbing structures—such as its elastic beak and partially spongy skull. They mimicked key parts of the bird’s head with a cylinder made of metal, rubber and porous glass. Diodes and other delicate devices inside the cylinder survived more than 99 percent of the time when they hit a wall with a deceleration 60,000 times that of gravity. Survival was only 74 percent in conventional shock absorbers.

Yoon, S.-H., and S. Park. A mechanical analysis of woodpecker drumming and its application to shock-absorbing systems. Bioinspiration and Biomimetics 6:016003 (January 17)