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News Tip


December 31, 2002

For more information on these science news and feature story tips, contact the public information officer listed at (703) 292-8070. Editor: Josh Chamot

Spider vs. Fly: Specialized Deception, Attack and Defense Rule the Conflict

It seems quite simple: Spider spins web. Fly gets caught in web. Spider spins silk lunch box around fly, feasting on the treat at a later time. End of story.

Not so, according to scientists studying the relationship between some spiders and flies under a National Science Foundation research award. It's more of a full-blown engagement involving specialized attacks, defenses, and purposeful deception.

Biologist George Uetz and fellow researchers examined the postures of the social orb-weaving spider, Metepeira incrassata, in relation to the sarcophagid fly, Arachnidomyia lindae (a specialized predator of Metepeira spider eggs) and the non-predatory domestic housefly, Musca domestica.

The study, published in the journal Behavioral Ecology and Sociobiology, suggests that a highly specialized predator's attacks may cause the evolution of predator-specific defensive responses in the prey.

Most spiders live a largely solitary existence, but a handful of species like the orb spider Metepeira live in social colonies. The sarcophagid fly attacks egg sacs at the spider colony and deposits a larva on the egg sac surface. Developing larvae eventually eat the eggs inside the sac.

The researchers noted that when a spider guards its egg sac against the sarcophagid fly, it assumes specific defensive postures to counter the fly's attack. This defense differs from responses to attacks by other flies.

When the researchers presented a domestic housefly to the spider, it was recognized as non-threatening. The researchers believe this response results from the spider's ability to distinguish between the sarcophagid fly's wing-beat frequency and the wing-beat frequency from a domestic housefly. This behavior can be likened to soldiers being able to distinguish a two-bladed helicopter from a three or four-bladed helicopter and adjusting their response accordingly.

But the story doesn't end there. The sarcophagid fly may pluck the spider's web to imitate the vibrations of captured prey, a ploy that tricks the spider into letting down its guard. In turn, the spider may cut the web thread relaying this distracting information, thereby preventing a lapse in defense of the valuable egg sac.

"What's neat about this is the number of ploy-counterploy interactions that have evolved," said Michael Greenfield, director of NSF's Animal Behavior Program. "Here, the interactions go back and forth as many as four times, a striking level of complexity in the realm of predator/prey behavior." [Manny Van Pelt]

If you would like to speak with a science expert on this topic, please contact Michael Greenfield [(703) 292-8421 /] or Steve Vessey [(703) 292-8421 /]

the sarcophagid fly
The sarcophagid fly, Arachnidomyia lindae, is a specialized predator of the eggs of the orb-weaving spider, Metepeira incrassata Metepeira.
Credit: George Uetz, University of Cincinnati
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(Size: 450KB) , or download a high-resolution TIFF version of image (6.34MB)

a common housefly
A common housefly is presented to the orb-weaving spider so scientists can study its response.
Credit: George Uetz, University of Cincinnati
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(Size: 143KB) , or download a high-resolution TIFF version of image (2.69MB)

the orb-weaving spider
The orb-weaving spider, Metepeira incrassata, is one of only a very few species of spiders that reside in social colonies.
Credit: George Uetz, University of Cincinnati
Select image for larger version
(Size: 602KB) , or download a high-resolution TIFF version of image (6.38MB)

arachnidomyia.wav This is the sound of Arachnidomyia lindae, a specialized predator of orb weaving spider egg sacs.

musca.wav This is the sound of Musca domestica, the non-predatory domestic housefly.

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A Short Brush with Greatness

a layer of cylindrical brushes on mica
Molecular resolution of a layer of cylindrical brushes on mica as measured by Atomic Force Microscopy.
Credit: Marcelo da Silva, UNC Chapel Hill
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(Size: 48KB)

Close-up of single brush molecules
Close-up of single brush molecules shows flexible backbones with hairy shells of densely grafted side chains.
Credit: Svetlana Prokhorova, University of Ulm
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(Size: 47KB)

A brush-shaped molecule found in cartilage has inspired researchers to develop a new group of synthetic "molecular brushes." As nanotechnology progresses, the brushes may find a range of applications, from inclusion within tiny nanomechanical devices to uses in osteoarthritis therapies.

New kinds of molecular brushes are coming out of the laboratories of Sergei Sheiko and Michael Rubinstein of the University of North Carolina at Chapel Hill (UNC) and Krzysztof Matyjaszewski of Carnegie Mellon University in Pittsburg, recipients of one of NSF's Nanoscale Interdisciplinary Research Team grants.

Sheiko presented initial results of their research at the Nanoscale Science and Engineering Conference held last week at the National Science Foundation in Arlington, Virginia.

Synthetic molecular brushes are made by joining "bristles" of chain-like molecules to a flexible handle or "backbone" -- the resulting structures look like miniature bottlebrushes. The molecules are soft cylinders about 100 nanometers long, roughly 1/1000th the diameter of a human hair. Each brush has the properties of an individual molecule, but is big enough to image and manipulate like a small particle.

The brushes have interesting mechanical properties because changes in temperature and pressure trigger changes in the backbone's shape. Brushes stretch, shrink and even turn from cylinders into spheres with changing conditions.

Their spring-like quality could make the brushes useful parts in micro-machines, where they could serve as cushions, pistons, and electrical contacts in ultra-small pumps or locomotives.

Although other groups have made molecular brushes, Sheiko says he and his colleagues, including collaborator Martin Moeller of the University of Aachen in Germany, are unique in creating and studying many types with the goal of producing "designer brushes" for different applications.

In addition to providing parts for tiny machines, the team's ability to manipulate brush characteristics might also help replace a structural component of human joints.

Natural molecular brushes in our cartilage, called proteoglycans, contribute to its strength. Loss of these molecules is one of the earliest signs of osteoarthritis, and the UNC team hopes their synthetic brushes could one day be used in novel therapies to treat the disease.

Alan Grodzinsky, director of the Massachusetts Institute of Technology's Center for Biomedical Engineering and a researcher developing artificial cartilage from human and animal cells, calls the group's work creating brushes "terrific." He adds that "if their molecules can be used by living cells to mimic the way the body makes cartilage, they could have important uses in the future." [Roberta Hotinski]

For more on nanotechnology at NSF, see:

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Researchers Discover Properties of Perovskite, Explain Why no Earthquakes Start in Earth's Lower Mantle

Scene from animation
"Animation of perovskite crystal structure under uniaxial pressure. The fundamental building blocks of the crystal structure adapt to the load by changing their orientation."

Credit: Jiuhua Chen, Mineral Physics Institute, State University of New York at Stony Brook

Researchers at the State University of New York at Stony Brook have found that the mineral perovskite's strength and character prevents earthquakes from starting in our planet's lower mantle (the lower part of the roughly 1,400-mile-thick envelope surrounding Earth's core). Perovskite is a dominant mineral in the lower mantle and critical to the mantle's physical properties.

Using x-rays from the Department of Energy's National Synchrotron Light Source (NSLS), NSF-supported researcher Jiuhua Chen and colleagues have measured the strength of perovskite at high pressures and temperatures.

Chen and his colleagues found that perovskite not only is stronger than other minerals at high pressure and under searing heat, it also has a pliant nature that is insensitive to temperature.

"The result revises the existing prediction for how material flows in Earth's lower mantle and supplies the first experimental evidence for understanding why earthquakes do not start in the lower mantle," said Chen.

Some earthquakes occur where adjacent tectonic plates catch, bursting forth when the pressure that builds over time is suddenly released. These are called near-surface or shallow earthquakes. Earthquakes can also start along a tectonic plate where one slab of crust pushes beneath an adjacent slab, sinking into the mantle. These are called deep earthquakes.

Seismic observations show no deep earthquakes starting in the lower mantle, but until Chen's research, the reason was not known.

Among many possible mechanisms for what starts an earthquake, said Chen, plastic instability may be largely responsible. Perovskite -- and Earth's lower mantle, it turns out -- are earthquake-resistant. [Cheryl Dybas]

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Extreme Micro-Networks Developed for Wireless Biosensors

retina chip
This is the retina chip developed at Wayne State University attached to a testing die. The small 1.5-mm portion (center) of the chip is the implantable device.
Photo Credit: Greg Auner, Wayne State University
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(Size: 49KB)

Larger versions (Total Size: 1,339KB) of all images from this document

 Note About Images

While setting up a wireless network in your house may be mostly a plug-and-play operation, a wireless network inside the human body changes the rules a bit. Putting one inside the human eye is a whole new ball game.

Networking researchers led by Loren Schwiebert at Wayne State University and Sandeep Gupta at Arizona State University, together with teams of sensor and chip designers, ophthalmologists and neurosurgeons are developing the first wireless networks for biomedical sensors.

With support from an NSF Information Technology Research award, the team is designing full-fledged networks that operate under extreme conditions, for decades at a stretch without repair, using almost no power, and in a biomedically safe manner -- all while avoiding interference and outside tampering.

Such networks are needed to expand the possibilities of artificial retinas, which are being developed by groups around the world, including a team at Wayne State led by Schwiebert's collaborator, and fellow awardee, Greg Auner.

Current retinal sensor chips hold an array of a few hundred electrodes, each representing a single retinal cell. An external camera on a pair of eyeglasses transmits image signals to the electrodes four or five times per second.

"You can put a tiny chip in someone's eye, and they'll see a spot of light, but people's goals in this area are bigger than that," Schwiebert said. An ideal artificial retina would include hundreds or thousands of sensor chips for receiving a high-resolution image. "However, retinal sensors present the worst-case scenario, since they're constantly on during waking hours," he said.

With all biosensors, researchers must minimize the energy involved in their operation, because some of that energy will dissipate as heat. Among other problems, excess heat could make a portion of the body habitable by unwelcome bacteria.

The heat issue forces tradeoffs in other aspects of the network. To understand these tradeoffs, Gupta and his students at Arizona State have been modeling electromagnetic signals inside body tissues and developing an energy-efficient communication system for establishing a wireless link from an external camera to the sensor chip in the eye.

The effects of cell phones and other radiation sources on human tissue have been carefully studied, but only from a safety perspective. For the first time, Gupta's team is looking at what happens when you try to send and receive signals inside the body.

The researchers have developed models and conducted simulations to examine the interplay of power, radio frequency, antenna size, signal-to-noise ratio and signal penetration depth that result in a reliable signal with a safe level of radiation absorption. Their preliminary results will be presented at several conferences in 2003.

The next step for Schwiebert will be to deploy an experimental network of sensor nodes in the lab. Unlike most networking prototypes that start with small-scale models, they will be working with a prototype considerably larger than life-size.

Because of the many opportunities and challenges presented by sensors and sensor networks, NSF recently announced a new $34 million initiative to advance fundamental knowledge of sensor design, networking, and applications. [David Hart]

For more on the Sensors and Sensor Networks program, see:

For the Networking Wireless Sensors Lab at Wayne State University, see:

For the Mobile Computing and Wireless Networking Lab at Arizona State University, see:

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