Samplings

March 2007

	Female Utetheisa ornatrix moth perched on its host plant, Crotalaria Photo by Hang-Kyo Lim

Female moths of the species Utetheisa ornatrix boost their chances of attracting a mate by pumping out sex pheromones in unison—the olfactory equivalent of chorusing frogs—according to new research. Hangkyo Lim and Michael D. Greenfield, both behavioral ecologists at the University of Kansas in Lawrence, tested females in the laboratory to find out whether they adjust their chemical signaling in the presence of other females. Females housed in groups began releasing pheromones sooner and continued to signal longer and with fewer interruptions than did isolated females. They also appeared to signal more vigorously: the group-housed females pumped their abdomens more rapidly, a behavior thought to enhance the release of pheromones.
     Until now, biologists had described sexual communication in moths largely as a straightforward interaction between signaling females and responsive males, which fly upwind toward the source of the pheromones they detect. Lim and Greenfield’s findings, however, show that female U. ornatrix moths also keep track of what their competitors are doing, suggesting that the story in that species is more complex.
     Unlike the males of most other moth species, U. ornatrix males mate infrequently compared with females, because it takes the males several days to produce a spermatophore—a kind of insect prenuptial gift that carries nutrients, toxins to ward off predators, and sperm. That valuable gift entices females to mate multiple times, another behavior unusual in moths. Those quirks lead to a circumstance fairly uncommon in nature: the sexually receptive females outnumber the males. Lim and Greenfield suspect that the competitive signaling behavior of U. ornatrix females stems from the surplus. (Behavioral Ecology)

—Nick W. Atkinson

View of the latrine area from the north, with the ancient Essene site of Qumran in the background Photo by Joe Zias (www.joezias.com)

The Dead Sea Scrolls, biblical texts written sometime before a.d. 68, were discovered in 1947 in caves near the ruined settlement of Qumran on the Dead Sea. But who were the scrolls’ scribes? Most scholars think at least some of them were members of an ancient Jewish sect called the Essenes who, they argue, lived at Qumran. Newly discovered evidence—of a decidedly worldly nature—bolsters that view.
     Two of the scrolls instruct religious adherents to build communal latrines some distance northwest of their city. Furthermore, Josephus, a Jewish historiographer of the first century a.d., wrote that the Essenes were adamant about defecating in “retired spots” and burying their feces. Evidence of buried feces a good distance northwest of Qumran, then, would connect the settlement, the Essenes, and the Dead Sea Scrolls.
     Feces can’t normally remain intact in the desert for hundreds of years. But the dead eggs of intestinal parasites can—so long as they are buried and thereby protected from sunlight and wind. Joe E. Zias, a paleopathologist at the Hebrew University of Jerusalem, led a team including James Tabor, Chair of the Department of Religious Studies at the University of North Carolina at Charlotte, that sampled the soil in and around Qumran. In only one area did they discover eggs from human intestinal parasites. As predicted, the site was about 400 yards northwest of the village (a nine-minute uphill hike, Zias determined) and hidden from view behind bluffs.
     Zias believes that the sect members, their mission accomplished, immersed themselves in a bath on their walk back down to the settlement. That sounds like a healthy practice, but the bathwater was anything but fresh: Qumran relied for water on runoff collected during a brief annual rainy season. Skeletal remains indicate a population in extremely poor health, possibly because disease-causing organisms were repeatedly carried from toilet to bath, where they flourished and infected new hosts. (Revue de Qumran)

—Stéphan Reebs

	To study individual and genetic variation in human odor, the research team traveled to a small village in the Austrian Alps. There nearly 200 people in sixteen families allowed the team to collected samples of their armpit sweat repeatedly over ten weeks. Photo by Konrad Lorenz Institute for Ethology/Dustin J Penn

Everyone has a special smell, often recognizable to other people and to dogs. New research, the most comprehensive study of human odor to date, shows that body odor is made up of a diverse array of volatile compounds. One’s own distinctive scent, moreover, comes from a personalized blend of those chemicals.
     A team led by Dustin J. Penn, an evolutionary and behavioral ecologist at the Konrad Lorenz Institute for Ethology in Vienna, collected samples of saliva, armpit sweat, and urine from nearly 200 people living

Photo © Milos V. Novotny  and Helena A. Soini /  Indiana University,  Bloomington, Indiana,  USA

in an Austrian village. Sweat, the team discovered, includes the greatest number of volatile compounds; the team counted 373 such compounds that subjects consistently produced throughout the ten-week study.
     Each person produced his or her own subset of the compounds. The subsets overlapped, yet individuals were readily distinguishable. Unsurprisingly perhaps, men and women tended to produce different mixtures—though no single compound differentiated the sexes. The study provides a new method for measuring a person’s baseline odor. Because body odor can change with the onset of illness, the method could lead to new ways of diagnosing disease. (Journal of the Royal Society Interface)

—S.R.

	Hot gas cloud from a supernova, a cosmic-ray source Photo from NASA / ESA / Johns Hopkins University

Cosmic rays—charged particles emitted by supernovas and other highly energetic sources in space—continually strike the Earth’s atmosphere. Most scientists, however, had assumed they could have little effect on terrestrial life. Then last year, Henrik Svensmark, a physicist at the Danish National Space Center in Copenhagen, published experimental evidence that cosmic rays could increase the formation of cloud droplets, with obvious implications for climate and thus for life. Now another study by Svensmark reveals a remarkable link between cosmic rays and the stability of biological productivity on Earth.
     Two main factors, Svensmark assumes, have accounted for most of the changes in Earth’s cosmic-ray exposure through geological time: the amount of shielding from cosmic rays afforded by the Sun’s magnetic field, and the rate of supernova formation throughout our Milky Way. Svensmark estimated the Sun’s shielding by studying other sunlike stars for clues to our star’s history, and the supernova rate from straightforward astrophysical records. He also estimated changes in Earth’s biological productivity through time by measuring the ratio of the isotopes carbon-13 to carbon-12 in ancient sediments. Life processes, such as photosynthesis, preferentially use carbon-12, so the higher the relative amount of carbon-13 left behind in sediment, the greater Earth’s biomass must have been when the sediment was deposited.
     Svensmark discovered that when cosmic rays were most intense (between 2 billion and 2.5 billion years ago, for instance), life was particularly unstable: periods of high productivity alternated with leaner times. Thus a surprising connection exists between distant supernovas and life on Earth: intense cosmic rays appear to cause climate fluctuations that bring on alternating periods of feast and famine. (Astronomische Nachrichten)

—S.R.

A coral grouper about to signal in front of a giant moray eel Photo by Redouan Bshary

Small fish on the coral reefs of the Red Sea face danger from all directions. Swimming in open water increases their chances of lethal encounters with hungry groupers, but hiding in a crevice exposes them to giant moray eels. It gets worse: a new study shows that the little fish’s pursuers are in cahoots.
     Redouan Bshary, a behavioral ecologist at the University of Neuchâtel in Switzerland, and three colleagues discovered that groupers shake their heads in a distinctive way to invite moray eels to leave their lairs and join the search for prey. The predators then set off together to patrol the reef; the eel sneaks through the rocks while the grouper waits to intercept fleeing prey. Similarly, the team found, if a grouper hunting solo chases its target into an inaccessible coral fissure, it sometimes gives a slightly different headshake to mobilize a nearby eel.
     Cooperative hunting between species had previously been noted only in humans hunting with dogs or dolphins. Even cooperative hunting among members of the same species is limited to a handful of mammals and birds, animals with relatively strong cognitive abilities. But Bshary’s study shows that the active collaboration between groupers and eels increases hunting success—for the groupers, at least—by as much as a factor of five. Once caught, prey are never shared, but Bshary’s group thinks the selfishness is actually the key to success because it eliminates competition for the kill. So long as both species benefit from the arrangement in the long run, it doesn’t matter which hunter happens to catch a particular fish. (PLoS Biology)

—N.W.A.

Blue whales (cow and calf) in coastal California waters near San Miguel Island Photo from the Protected Resources Division, Southwest Fisheries Science Center, NOAA Fisheries Service

Blue whales, the biggest creatures on Earth, have the deepest voices: most of their vocalizations are pitched far too low for people to hear. Their songs repeat a series of eerie tones, blips, and creaks and may carry on for hours or even days. To human ears, the alien, barely audible songs are all but indistinguishable. A new study shows, however, that the leviathans sing several variations on the “blues,” each correlated with a particular region of the sea.
     Mark A. McDonald, an acoustician at Whale Acoustics, a company in Bellvue, Colorado, and two colleagues examined thousands of sound spectrograms computed from blue-whale songs recorded around the world since 1959. They found they could visually classify the spectrograms into nine distinct groups, each corresponding to a particular geographic region.
     Blue whales of both sexes make short calls, but only the males are known to sing, suggesting the songs may enable them to attract mates or advertise their presence to other males. (Under certain conditions their songs can travel thousands of miles, communicating to other whales across vast ocean distances.) If so, each song group may be characteristic of a particular blue-whale population: after all, mating calls should attract compatible mates.
     Songs, McDonald’s team proposes, could become a convenient, noninvasive, low-cost way for biologists to keep track of blue-whale populations—though distinguishing animal groups by their behavior instead of their physical or genetic characteristics remains controversial. (Journal of Cetacean Research and Management)
     [Listen to blue whale songs online.]

—Rebecca Kessler

Picture of a gash on the south side of Khufu’s Pyramid, blasted in the nineteenth century by the Egyptologist Colonel Richard William Howard Vyse: The blocks inside the gash appear carved, while those on the periphery, especially the bottom, appear cast. Photo by Michel Barsoum

How the ancient Egyptians built the Great Pyramids of Giza nearly 5,000 years ago, using only manpower and copper tools, is one of Egypt’s enduring mysteries. Their most impressive creation, the pyramid of Khufu, stands forty-five stories tall and is made up of some 2 million massive, three-ton blocks, some of which fit together flawlessly.
     Most Egyptologists think crews of workers cut the blocks from nearby limestone quarries, carved them with copper chisels, and hoisted them into place with immense ramps, levers, and wedges. But the absence of supporting evidence—no ramps, tools, or limestone waste piles remain—has given rise to alternative, and often controversial, explanations.
     Now Michel W. Barsoum, a materials scientist at Drexel University in Philadelphia, and two colleagues have discovered evidence that could finally settle the issue—though in the meantime it has certainly fueled debate. The team examined samples from two pyramids at Giza and from local limestone formations with an electron microscope and analyzed the samples chemically. Their results support a two-decade-old idea: parts of the Great Pyramids were built not of carved limestone blocks but of concrete casts.
     In ancient Egyptian concrete, Barsoum says, limestone particles were mixed with a silica-rich binder. The ingredients could be transported in manageable quantities, then poured on site.
     If confirmed, Barsoum’s discovery will burnish the already impressive reputation of Egyptian builders: they would get credit for inventing concrete. And their recipe may point toward a clean, inexpensive, long-lasting substitute for portland cement, which is widely used today but highly polluting. (Journal of the American Ceramic Society)

—Graciela Flores

For further details see Engineering the Pyramids.

The Warming Earth

Warm Down, Cool Up

Many satellites orbit Earth in the thermosphere, between sixty and 500 miles above the surface. Air is pretty thin up there, of course, but in the long run it’s enough to make satellites slow down and fall to a lower orbit, a phenomenon known as orbital decay.
     Orbital decay has been less pronounced in recent years, and that can mean only one thing: the thermosphere is thinning, which in turn means it’s cooling. Here’s where the story strikes closer to home. By burning fossil fuels people have been releasing ever more greenhouse gases—carbon dioxide (CO₂), in particular. And though CO₂ warms the lower atmosphere, it cools the thermosphere, because at those rarefied heights it converts the energy of collisions with other molecules to heat that radiates into space.
     Liying Qian and Stanley C. Solomon, both atmospheric scientists at the National Center for Atmospheric Research in Boulder, Colorado, and two colleagues have taken advantage of satellite tracking to test a computer model of how the thermosphere responds to input energy. In their model, the investigators calculate how much the thermosphere has cooled in the past thirty years by estimating the contributions of two factors: variations in solar activity (which warms the thermosphere directly) and changing levels of CO₂. They found good agreement between their model and the temperature as measured independently by satellite orbital decay. Their model confirms that CO₂ has indeed cooled the thermosphere, and it predicts a further cooling of 3 percent by 2017.
     If the useful life-times of satellites depended on physics rather than on budgets, maybe excess CO₂ would be good for something, after all. (Geophysical Research Letters)

—S.R.

Many bird species in the United States are shifting their breeding ranges northward, a new study shows. Similar northward shifts have been observed in Great Britain, so the cause of both is probably the same. Global warming is the likeliest suspect.
     The new study comes from data gathered by the Breeding Bird Survey (BBS), a program run by the U.S. Geological Survey and the Canadian Wildlife Service. Each year, skilled birders spend a summer day driving or walking along more than 4,100 road segments of the U.S. and Canada, identifying the bird species they hear or see along the way. Because the survey has continued uninterrupted since 1966, its data enable ornithologists to analyze long-term population trends.
     Alan T. Hitch and his graduate adviser, Paul L. Leberg, a conservation biologist at the University of Louisiana at Lafayette, report that out of twenty-six southern–U.S. species they studied in the BBS records, nine have significantly pushed the northern limits of their breeding ranges northward since the late 1960s. The northward shifts vary from twenty-six miles for summer tanagers to more than 200 miles for great-tailed grackles. At the same time, the northern limits of only two of the twenty-six species, Bachman’s sparrows and Bewick’s wrens, have retreated southward.
     Hitch and Leberg say the diversity of the nine southern species shows they are not being drawn northward by some specific factor in the midlatitudes—more bird feeders, for instance. Nor are their ranges simply expanding. If that were the case, northern species should have expanded their ranges southward, too, and there was no systematic indication of that. Instead, rising temperatures seem to be nudging southern ecosystems northward. (Conservation Biology)

—S.R.

Copyright © Natural History Magazine, Inc., 2007