- Hidden Messages Found in Bird Nest Decorations
- Multiple Asteroid Strikes May Have Killed Mars’s Magnetic Field
- All-Nighters Make Bodies Hoard Calories
- Slime Molds Are Earth’s Smallest, Oldest Farmers
- The Mass Extinction of Scientists Who Study Species
- Introducing: Daniel MacArthur of Genetic Future
Posted: 20 Jan 2011 01:49 PM PST
The discovery of messages in raptors' nests has raised the possibility that many bird species encode signals into these structures, with seemingly decorative flourishes actually full of meaning.
Among black kites, scraps of white plastic are used to signal territorial dominance. To other kites, the scraps are a warning sign. To humans, they hint at an unappreciated world of animal communication.
"It's probably very common that other bird species decorate their nests in ways compatible with what we found," said Fabrizio Sergio, a biologist at the Doñana Biological Station in Spain. "And not only birds, but fish and mammals."
A few species, such black wheateaters and bowerbirds, are already known to use nest design in courtship displays. But such communication is considered uncommon and relatively one-dimensional, aimed entirely at finding a mate.
Other, ubiquitous forms of decoration — colorful ribbons and man-made trinkets, or flowers and bright grasses, found in the nests of hundreds of species — have been dismissed as insignificant adornment.
"Whenever you enter their nests, you'd see all these strange materials. Almost anybody that has started to study kites has talked about this," said Sergio. "But it was only five years ago that we started" looking at it carefully.
In a study published Jan. 21 in Science, Sergio's team describes its careful observations of 127 black kite nests in Spain's Doñana National Park.
They found that, several weeks before females laid eggs, birds festooned their nests with pieces of white plastic. Fitter birds, in possession of the best territory, tended to use more plastic. Weaker birds, with less-desirable territory, used less. Elderly and very young birds used none.
Territorial confrontations are common among kites, and proved closely linked to displays of plastic. Kites with much plastic in their nest were rarely challenged, while those with little were challenged daily, even hourly.
The plastic appears to be a convenient way of codifying and announcing strength, saving kites from indiscriminate or ill-chosen battles. The birds also had access to green and transparent plastics, ostensibly preferring white because of its long-distance visibility.
When the researchers intruded, however, adding extra plastic to nests, challenges paradoxically became more frequent — suggesting that kite community is aware of existing claims, and quick to test would-be cheaters.
Sergio is currently conducting a long-term study of nest decoration, hoping to see how it changes over the kites' multi-decade lifetimes. He would also like to know the origins of nest decoration, and whether — like birdsong — it has both genetic and cultural components.
Meanwhile, other ornithologists might look for messages among more bird species. Sergio stressed that territoriality is only one type of message; there could be many more, and each needs to be studied and interpreted.
"There are countless examples of storks and magpies and crows and swans decorating their nests," he said. "We think that they're not taking some funny material to their nest, but signaling other individuals."
Images: 1) Black kite nest./Fabrizio Sergio. 2) A black kite pair./Fabrizio Sergio. 3) A magpie nest festooned with ribbon and horsehair./minicooper93402/Flickr.
Citation: "Raptor Nest Decorations Are a Reliable Threat Against Conspecifics." By F. Sergio, J. Blas, G. Blanco, A. Tanferna, L. López, J. A. Lemus, F. Hiraldo. Science, Vol. 331 No. 6015, January 21, 2011.
Posted: 20 Jan 2011 10:01 AM PST
Once upon a time, Mars had a magnetic field, just like Earth. Four billion years ago, it vanished, taking with it the planet's chances of evolving life as we know it. Now scientists have proposed a new explanation for its disappearance.
A model of asteroids striking the red planet suggests that, while no single impact would have short-circuited the dynamo that powered its magnetism, a quick succession of 20 asteroid strikes could have done the job.
"Each one crippled a little bit," said geophysicist Jafar Arkani-Hamed of the University of Toronto, author of the new study. "We believe those were enough to cripple, cripple, cripple, cripple until it killed all of the dynamo forever."
Rocky planets like Earth, Mars, Mercury and even the moon get their magnetic fields from the movement of molten iron inside their cores, a process called convection. Packets of molten iron rise, cool and sink within the core, and generate an electric current. The planet's spinning turns that current into a magnetic field in a system known as a dynamo.
Magnetic fields can shield a planet from the constant rain of high-energy particles carried in the solar wind by deflecting charged particles away from the surface. Some studies have suggested that Earth's magnetic field could have protected early life forms from the sun's most harmful radiation, allowing more complex life to develop. But traces of magnetism in the Martian surface reveal that the red planet lost its magnetic field some four billion years ago, leaving its atmosphere to be dessicated by the harsh solar wind.
Previous studies suggested that a massive impact could have shut down Mars's dynamo by warming the mantle layer, disrupting the heat flow from the core to the mantle and shutting down convection. The fact that the crust of Mars's younger impact craters is not magnetized supports this idea. Earlier computer models by geophysicist James Roberts of Johns Hopkins University showed that the largest known impacts on Mars could turn the mantle to a warm blanket, bringing the dynamo to a standstill.
But Arkani-Hamed's new study in the Journal of Geophysical Research suggests that just one impact wouldn't suffice. The dynamo would recover in less than one hundred million years. "The magnetic field should come back again," he said.
To make his case, Arkani-Hamed modeled the heat that could have been produced when — according to some geophysicists — an asteroid the size of Texas hit Mars about 4.5 billion years ago, producing the biggest impact in our solar system's history. Called the Borealis impact, it may have flattened Mars's entire northern hemisphere.
This mega-impact would have flattened out the heat cycle inside the planet, too, snuffing out the dynamo within about 20,000 years. Without the cold compress of the mantle to siphon heat away from the core, convection wouldn't have a chance.
But left alone, convection would have recovered in the outer parts of the core, and eventually penetrated deep and started the whole core churning again. The Borealis impact would have crippled the dynamo, but not killed it outright.
"If there were a dynamo at 4.5 billion years, it could cease, go away and regenerate after about 100 million years," he said.
But perhaps several impacts in a row could do the job. The planet's crater record shows that Mars suffered 20 impacts in quick succession between 4.2 and 3.9 billion years ago. In work to be presented at the Lunar and Planetary Science Conference in The Woodlands, Texas this March, Arkani-Hamed teamed up with Roberts to show that just the five largest of these impacts could have shut down the magnetic field. The impacts came so rapidly that the dynamo had no time to recover before the next crippling blow arrived.
"This research is important because it shows that this scenario is plausible. It could have physically happened," said Wesley Watters of Cornell University, who was not involved in the new research. "But to test this model versus another is enormously difficult to do."
To really figure out when and how Mars lost its magnetic field, we'd need to know the ages of lots of Martian rocks with the same kind of precision with which we know them on Earth.
"We just don't have that for Mars," he said.
Posted: 20 Jan 2011 07:29 AM PST
Staying up all night clearly taxes the body, but scientists have only now added up the exact bill. By measuring the actual number of calories the body expends to fuel an all-nighter versus a good night's sleep, researchers from the University of Colorado at Boulder calculate that a full night of sleep helps the body conserve as much energy as is in a glass of warm milk.
Missing a night of sleep forces the body to burn about an extra 161 calories than it would have during eight hours of sleep (not counting what's used in moving around while awake), but it's no weight-loss miracle: The body tries to make up for the deficit by saving more energy than usual the next day and night, researchers report in the January Journal of Physiology.
The measurements, the first to put precise numbers on how much total energy people use in a 24-hour period while asleep, awake or recovering from a night of sleep deprivation, help bolster a theory that an important function of sleep is to save energy (SN: 10/24/09, p. 16).
To measure how much energy people use during sleep in a more rigorous way than has been done before, Kenneth Wright, a physiologist at the University of Colorado, and his colleagues studied seven people. Each of the healthy young volunteers lived inside a sealed room for three days. The volunteers were on bed rest the entire time and ate the same amount of calories at the same time each day. The researchers continually monitored the subject's brain waves and how much oxygen and carbon dioxide the person breathed in and out. From there, the team could calculate each person's energy use during each stage of sleep and waking.
"This is a Herculean effort," neurobiologist Paul Shaw of Washington University in St. Louis says of the study. "This will be the gold standard going forward."
Recently, scientists had dismissed energy conservation as sleep's most important mission. "Sure, there's energy savings, but it's not worth much. It's a hot dog bun or a cup of milk's worth," Shaw says of many scientists' attitude toward the amount of calories the body saves during sleep. But "small differences can have large consequences," says Shaw, who was not involved in the current research.
Wright notes that eating just 50 extra calories per day over an extended period can lead to obesity. So, he contends, the amounts of energy savings associated with sleep aren't trivial. But would-be dieters shouldn't interpret the new data as pointing to sleep deprivation as a weight-loss plan, Wright says. Many studies have linked chronic sleep deprivation with obesity and other health problems (SN: 10/24/09, p. 28).
After staying up all night, volunteers burned about 28 fewer calories during eight hours of recovery sleep than they had during a full night of regular sleep. And the energy conservation didn't stop there. In the 24-hour period during which people caught up on missing sleep, they burned about 228 fewer calories than during a comparable period in which they were sleep-deprived. Overall, when people slept normally, they expended 96 more calories than they did on days when they were making up for lost sleep.
Volunteers were limited to eight hours of recovery sleep, and the effect might have been even greater if the researchers had allowed volunteers to fully sleep off their sleep debt, Wright says.
Shutting down muscles and other body functions during sleep might save the body even more energy than measured, but the body does have crucial energy requirements in other areas. The body may be using energy to fuel essential sleep functions such as rewiring connections between brain cells, boosting the immune system and regulating hormones, the researchers speculate. Sleep-deprived people are diverting some of the energy needed for those important processes, says Wright. "It's not worth the cost."
Chronic sleep deprivation caused by conditions like sleep apnea and insomnia might exact a high energetic toll, Wright says. Each time volunteers awakened from sleep at night, energy consumption shot up, even if the episode lasted only seconds, the researchers report. People with sleep apnea rouse many times during the night, raising the possibility that they are tapping energy reserves needed for sleep's other functions, Wright says.
Next, the researchers hope to learn whether missing a few hours of sleep each night over several days has different energy costs than staying up all night.
Posted: 19 Jan 2011 01:20 PM PST
Colonies of a bizarre microbial goo have been found practicing agriculture at a scale tinier than any seen before.
Animals such as ants, snails and beetles are known to farm fungus. But the slime mold's bacterial-farming trick takes it into a whole new realm..
"If you can pack your food source with you, it's a serious advantage," said molecular biologist Debra Brock of Rice University, co-author of the slime-mold study, published Jan. 19 in Nature.
Dictyostelium discoideum, the best-known of a group of creatures called slime molds, spends part of its life as a single-celled amoeba feeding on bacteria that grow in decomposing leaves on forest floors.
When food is short, hundreds of thousands of amoebas come together, fusing into a single entity. It may crawl off as a slug in search of richer pastures, then form a stalk topped by a "fruiting body" that bursts to disperse a few lucky amoebas-turned-spores. Or it may form the stalk right away, without crawling.
It's been thought that slime molds simply scavenge, eating bacteria they like and oozing out the rest. In laboratories, researchers "cure" slime molds of their bacteria by allowing them to purge themselves on Petri dishes. But Brock, who studies how slime-mold cells communicate and self-organize, kept finding bacteria in the fruiting bodies of some slime molds and not others.
When grown in the lab, the unusual fruiting bodies grew both the slime mold and the bacteria.
"The typical response to finding two species in a culture is, 'Ick, I don't want this!'" said evolutionary biologist Kevin Foster of Oxford University, who wasn't involved in the study. "[Brock's team] had the insight to realize this was more than a simple contamination, that something else was going on here."
Brock's team took new samples of different slime molds in the wild, growing them with careful attention to their dietary and excretory habits. They found that some strains didn't gorge themselves and "lick the plate clean" of bacteria, but instead saved some inside of the colony. They were farmers, and fared better in some soils than their nonfarming counterparts.
In another experiment, the researchers gave antibiotics to their slime molds, killing off the colonies' bacteria. When Brock's team reintroduced bacteria, the farmers absorbed multiple strains, keeping some but not eating all of them. Nonfarmers simply consumed bacteria or left them behind.
Follow-up experiments are underway to see what genes may differ, if any, between farmers and nonfarmers.
Foster said he'd like to know where farmed bacteria hide when slime molds form spores. "If they're taken inside spores, that's even stronger evidence of an adaptation for farming," he said.
In an accompanying commentary, University of Copenhagen biologist Jacobus Boomsma noted that "the ancestors of these slime molds were among the earliest colonizers of terrestrial habitats, so the history of this bacterial-husbandry symbiosis may go back further than any other farming system."
"They may well possess unknown adaptations that, if revealed, would illuminate fundamental questions of conflict and cooperation across species boundaries," Boomsma wrote.
"As humans, we have very intimate relationships with microorganisms," Brock said. "[Slime molds] have amazing similarities to humans, with all kinds of developmental genes similar to ours, and even have immune systems. We can use them to attack basic questions about ourselves."
Images: 1) Scanning electron microscope image of Dictyostelium discoideum in several developmental stages. Shown in this image are slime molds growing stalks topped with spore-filled balls (top, left to right), as well a slug (bottom left) and mounds (bottom center)./M.J. Grimson & R.L. Blanton via Dictybase.org. 2) A light microscope photograph of D. discoideum fruiting bodies./Scott Solomon.
Video: A yellow slime mold (not D. discoideum) grows over 5 hours on a log./Vimeo/sesotek.
Citations: "Primitive agriculture in a social amoeba." By Debra A. Brock, Tracy E. Douglas, David C. Queller & Joan E. Strassmann. Nature, Volume 469 Number 7330, Jan. 20, 2011.
"Farming writ small." By Jacobus Boomsma. Nature, Volume 469 Number 7330, Jan. 20, 2011.
Posted: 19 Jan 2011 10:30 AM PST
We are currently in a biodiversity crisis. A quarter of all mammals face extinction, and 90 percent of the largest ocean fish are gone. Species are going extinct at rates equaled only five times in the history of life. But the biodiversity crisis we are currently encountering isn't just a loss of species, it's also a loss of knowledge regarding them.
Scientists who classify, describe and examine the relationships between organisms are themselves going extinct. The millions of dollars spent globally on technology to catalog species may actually be pushing out the people we rely upon: taxonomists and systematists. We're like young children frantic to add new baseball cards to our collections, while the actual creators of the baseball cards themselves are vanishing.
From the Fields is a periodic Wired Science op-ed series presenting leading scientists' reflections on their work, society and culture.
Take for example the aplacophorans, a rare rare group of invertebrates closely related to octopuses, squids, snails and clams. Most of us will never see even one of the approximately 360 known species of small (less than a couple of inches long) aplacophorans that inhabit ocean depths greater than 50 feet. But, ignorance of this group is not limited to the public.
Fewer than two dozen scientific papers have been published on the group since 2005, even though many new species await discovery and description. And most of these studies were done by one scientist, the venerable Amélie Scheltema of Woods Hole Oceanographic Institute. As she edges closer to retirement, she may sadly become the last to study aplacophorans.
If 50 percent of the species of aplacophoran went extinct tomorrow, we would never know.
Amelie's story is tragically common. Martin Sørensen of the Natural History Museum of Denmark is one of the very few active kinorhynch, or mud-dragon, taxonomists. Martin also represents one of only two living taxonomists who have studied gnathostomulids. The other, Wolfgang Sterrer, is retired.
Both kinorhynchs and gnathostomulids are small, less than one-tenth of an inch in length, and dwell in between grains of sand and mud on the ocean floor. Fewer than 300 species are described from both of these phyla — the broadest classification scientists group animals into — and our knowledge of them is based almost entirely on collections from the well-explored eastern coast of the United States, the Mediterranean and the west coast of Europe.
"Even within these areas new species appear quite often, and when I collect outside [these areas], I always expect to find undescribed taxa exclusively," Sørensen wrote in a recent e-mail to me. His new work in the East China sea has already uncovered 15 new species. Indeed, the morning he e-mailed me, Sørensen, looking through his microscope, had just discovered another new species.
"The number of taxonomists working on these obscure taxa has always been rather low (which explains our limited knowledge about them), but within the last 20 years taxonomy as a discipline has come under even harder pressure which has resulted in a further decline in the number of experts," Sørensen wrote.
This problem plagues well-known groups, too. For example, nematodes represent more than 28,000 described species of freshwater, marine, terrestrial and parasitic roundworms. On the seafloor they account for 85 to 95 percent of all organisms. But a new study found the number of scientific papers describing new nematode species is half of what it was a decade ago, and a third of the decade before that. Anywhere between 10,000 and 100,000 species remain undescribed.
Why the loss of taxonomists? Because we have devalued their contributions, both monetarily and scientifically.
Some attribute the decline of these researchers to the replacement of outdated methods that would not meet the scrutiny of science today. These critics envision taxonomists as lone museum scientists surrounded by dusty wood cabinets and bottles of formaldehyde where species description is more art than science. But this portrayal overlooks the suite of modern genetic methods that those interested in discovery and description of new species use with increasing frequency.
This new breed of taxonomists includes Chris Mah of the Smithsonian National Museum of Natural History and Adrian Glover of the Natural History Museum in London, who are among the world's leading experts on sea stars and marine worms, respectively. Both demonstrate that the most informative science comes from synthesizing genetic techniques with more classical taxonomy based on knowledge of the anatomy and natural history of organism.
Extinction of taxonomists continues despite a growing pool of funds for biodiversity programs and databases. EUNIS, EOL, OBIS … the list goes on. These databases have pooled our collective biodiversity knowledge, helping identify what drives biodiversity and set conservation priorities.
Thankfully (my own research has relied upon them), thousands of hours and millions of dollars have been spent on these initiatives. However, many of these programs did not financially support taxonomists generating the data these databases required.
After a decade and 650 million dollars, the Census of Marine Life represents one of the largest initiatives to document biodiversity on our planet. In some regards, it was a great success, supporting 2,700 scientists to produce 2,600 new scientific publications and thousands of new species descriptions. But as the Census ends this year, no agency or organization is offering to fill the funding void previously filled by the Alfred P. Sloan Foundation.
Perhaps more importantly, the Census, like many initiatives, did not provide long-term positions and appointments for those doing taxonomic work. Many biology departments within universities no longer employ a taxonomist. The remaining positions are relegated to museums.
Why? As Sørensen explains, "The declining number of taxonomists and systematists is at least to some extent linked to the fact that your scientific production today should be measurable." And the units of measurement are collected grant money or the impact factor of a journal paper. Taxonomy has never been considered hot, and pure taxonomic studies are rarely funded, he wrote. Departments need grant money to operate.
Science as an institution may also be partly responsible for undercutting taxonomic work. Although a crude metric fraught with several issues, we measure the impact of a scientific paper by how many times other scientific papers have cited it. Similarly, we measure the impact of scientists by counting their cumulative citations. Unfortunately, taxonomic work is rarely cited, even when it should be.
On the other hand, the brilliant biodiversity databases we have created lead to a plethora of scientific papers. The Paleobiology Database, a comprehensive online catalog of fossil species, has already generated more than 100 publications. But the requirement for using this database, like most others, is citation of the database itself, not the nearly 35,000 papers generating the original data.
The decline in taxonomists means that at some point in the future we will be unable to train new generations of taxonomists. This problem is recognized by the National Science Foundation ,which in 1994 created a program to enhance taxonomic research. But while this initiative provides training, it does not create job opportunities.
Other problems are taking form too. For example, in 2006 I set out to explore how biodiversity and body size were linked among animals. To do so I needed information on the largest- and smallest-sized species for each group of animals — something surprisingly not readily garnered from the published literature.
I relied on my connections with taxonomists for guidance and information, but for many groups I struggled to find a contact. Even for well-known animals, I was amazed by how few scientists still studied them.
My personal experience highlights how progress in biology as whole may be impeded if we lose taxonomy. The problem we face is a loss of knowledge not yet recorded in the scientific literature. In our technological efforts to concentrate our biodiversity knowledge, we may be rendering a field and body of knowledge obsolete.
And in the process, we may be undermining our own efforts to protect biodiversity.
Images: 1) NOAA. 2) Craig McClain.
Posted: 19 Jan 2011 06:00 AM PST
Wired Science Blogs is delighted to welcome a new addition to our fleet of awesome: Daniel MacArthur of Genetic Future. A postdoctoral genomics researcher in the United Kingdom by day, science blogger by night, Dan writes about the fast-moving world of human genetics and the companies offering to sell you information about your own DNA. His goal on Genetic Future is "to provide readers with the knowledge and tools they need to gain access to their own genome, make sense of the information it contains, and use that information sensibly."
Dan has been blogging about the emerging direct-to-consumer genetic-testing industry for three years, previously at ScienceBlogs.com and currently on Genomes Unzipped. There he and other genetics experts write about developing new analysis programs using their own genomes, which are freely available online. Dan hopes his efforts will "provoke discussion about the benefits, risks and limitations of genetic information and the challenges of genetic privacy."
Wired Science Blogs is a network of independent science bloggers hosted on Wired Science. The addition of Genetic Future will bring the network total to seven blogs, including Clastic Detritus, Dot Physics, Frontal Cortex, Laelaps, Neuron Culture, and Superbug.
We hope you'll enjoy reading Genetic Future in its new home. Go stop over and say hello using the newly installed DISQUS commenting system, which makes it easier than ever to participate in our ongoing discussions.
Image: Circos, an information aesthetic for comparative genomics/Genome Research.
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