Story ideas from the Proceedings of the National Academy of Sciences

PNAS tipsheet for June 8-12

ARTICLE HIGHLIGHTS

• Math model for Web-based information networks
• Tearing down termites' defenses
• Fire mitigation treatments are often misplaced
• How snakes slither
• Biodegradable fluorescent polymers

ALSO OF INTEREST

• Paleoindian settlements beneath the Great Lakes
• REM sleep enhances creativity
• Genetic mutation that may cause gout

Researchers have created a mathematical model that captures the rich network structures that emerge from annotations on social bookmarking websites. Vittorio Loreto and colleagues borrowed concepts from statistical physics and network analysis to develop a model of social annotation systems, which allow users to tag posts with relevant keywords. These systems, like those on the websites del.icio.us and BibSonomy, which the authors studied, have emerged as critical tools to create information networks across the globe. The authors found that features of the information networks produced by annotations can be captured by regarding the social annotation process as a series of "random walks," which is a concept used in statistical physics to describe a trajectory achieved by a series of steps that are not predetermined and occur arbitrarily. The modeling framework reproduced several aspects of the social annotation networks on del.icio.us and BibSonomy, including the growth of the size of the vocabulary used by the community and its network structure. Because these networks rely on human cognitive, behavioral, and social aspects, this research may aid in an understanding of the potential impact web-based systems will have on our societies, according to the authors.

Article #09-01136: "Collective dynamics of social annotation," by Ciro Cattuto, Alain Barrat, Andrea Baldassarri, Gregory Schehr, and Vittorio Loreto.

MEDIA CONTACT: Vittorio Loreto, Dipartimento di Fisica, Sapienza Universita' di Roma, Rome, ITALY and Fondazione ISI, Torino, ITALY; tel: +39-06-4491-3461 (day), +39-348-481-7746 (evening); e-mail: vittorio.loreto@roma1.infn.it

MEDIA CONTACT: Ciro Cattuto, Fondazione ISI, Torino, ITALY; tel: +39-011-660-3555, +39 340- 172-5467 (evening); e-mail: ciro.cattuto@gmail.com

Insect pests can be killed by blocking a component of their immune system with a sugar derivative, researchers have found. The results may provide a non-toxic, sustainable method for protecting crops and buildings against termites and other destructive insects. Ram Sasisekharan and colleagues found that blocking the actions of termites' Gram-negative bacteria binding proteins leaves termite nests vulnerable to bacterial and fungal infections that can attack and kill the termites. Termites normally secrete a form of an antimicrobial protein into their nests to prevent these pathogenic infections. The authors report a technique to block the protein's effects with a naturally occurring derivative of glucose called GDL. The researchers found that adding GDL to termite nests caused the termites to die more quickly at the hands of fungi that normally infect termites, as well as other opportunistic bacteria. The authors suggest that GDL, which is nontoxic and biodegradable, and other similar molecules could be developed for food processing and storage and in building materials to protect against insect attacks. Plants could be engineered to produce GDL at high amounts in specific locations to increase their immunity, the authors suggest.

Article #09-04063: "Targeting antimicrobial effector function in insect immunity as a pest control strategy," by Mark S. Bulmer, Ido Bachelet, Rahul Raman, Rebeca B. Rosengaus, and Ram Sasisekharan

MEDIA CONTACT: Ram Sasisekharan, Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA; tel: 617-258-9494; e-mail: rams@mit.edu

Only a small percentage of National Fire Plan treatments in the United States are implemented near where people live and work, researchers have found. A study suggests that federal efforts are likely not effectively mitigating the threat of wildfire to homes and people in the western United States. Tania Schoennagel and colleagues examined 44,000 fuels treatments (a type of controlled burning to clear excess flammable material from a forest) implemented between 2004 and 2008 and found that only 11 percent of the treated area was within 2.5 km (1.5 miles) of the wildland-urban interface where fires are most dangerous to people. Fire mitigation far from houses may have only small benefits, and is most effective near the wildland-urban interface. However, more than 70 percent of this zone is privately owned, which limits the ability of federal agencies to conduct fire-risk reduction treatments near communities. The authors suggest that although expansion of humans into former wildlands, warmer and drier summers, and flammable invasive tree species can lead to an increased risk of fires, better development planning and cooperation and cost sharing between government and private entities can help limit the fire risks.

Article #09-00991: "Implementation of national fire plan treatments near the wildland-urban interface in the western U.S.," by Tania Schoennagel, Cara R. Nelson, David M. Theobald, Gunnar C. Carnwath, and Teresa B. Chapman

MEDIA CONTACT: Tania Schoennagel, Department of Geography, University of Colorado, Boulder, CO; tel: 303-818-5166 (day); e-mail: tschoe@colorado.edu

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The physical mechanisms that snakes use to slither have been the subject of much debate. Previous analyses have assumed that snakes push against rocks and trees to propel themselves forward. David Hu and colleagues examined how snakes move and suggest that friction caused by the snake's skin plays a critical role in its ability to propel itself along a flat surface. Snakes use many techniques to move; Hu's team focused on "lateral undulation" in which the snake presses its belly laterally against an object to propel forward. To test their hypothesis, the authors used 10 juvenile pueblan milk snakes and tested the sliding ability of the snakes when their belly scales were covered in a cloth of similar thickness and roughness, and when their scales were covered with a much slicker fiberboard. The authors show that the belly scales perform a vital function: they snag on the irregularities on rough surfaces, which helps the snake slither laterally. The findings provide the foundation for limbless locomotion, which could lead to development of robotic snake-like organisms that can slither across flat surfaces such as sand, which lack obvious push points.

Article #08-12533: "The mechanics of slithering locomotion," by David L. Hu, Jasmine Nirody, Terri Scott, and Michael J. Shelley

MEDIA CONTACT: David Hu, School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA; tel: 404-894-0573; e-mail: hu@me.gatech.edu

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Newly developed artificial fluorescent polymers may enable researchers to monitor the growth of tissue in culture, according to a report. Although fluorescent dyes and quantum dots are widely used in bench research, longer-term use of these reagents in living tissue is made difficult by their toxicity. Jian Yang and colleagues developed an alternative: biodegradable fluorescent polymers, which can serve as scaffold materials in tissue engineering, drug delivery, and bioimaging. The authors modified the fabrication process for polymers that they had previously produced by introducing an amino acid along with citric acid in a chemical reaction. Based on experimental evidence, the authors propose that a ring shape--essential for fluorescence--forms when key atoms of the amino acid join the polymer backbone. The researchers suggest that the choice of amino acid influences the strength and wavelengths of fluorescence. The fluorescent polymers, which can be processed into membranes, are nontoxic to fibroblasts and induced only mild inflammation in mice over a 5-month period, according to the authors.

Article #09-00004: "Development of aliphatic biodegradable photoluminescent polymers," by Jian Yang, Yi Zhang, Santosh Gautam, Li Liu, Jagannath Dey, Wei Chen, Ralph P. Mason, Carlos A. Serrano, Kevin A. Schug, and Liping Tang

MEDIA CONTACT: Jian Yang, Department of Bioengineering, University of Texas at Arlington, Arlington, TX; tel: 817-272-0562; e-mail: jianyang@uta.edu

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Paleoindian settlements beneath the Great Lakes

An Acoustic and video survey of the bottom of Lake Huron reveals evidence of ancient Paleoindian hunting settlements.

Article #09-02785: "Evidence for early hunters beneath the Great Lakes," by John M. O'Shea and Guy R. Meadows

MEDIA CONTACT: John O'Shea, Museum of Anthropology, University of Michigan, Ann Arbor, MI; tel: 734-763-5795; e-mail: joshea@umich.edu

Rapid eye movement (REM) sleep improves creativity for solving novel problems by enhancing associations between new and previously learned information.

Article #09-00271: "REM, not incubation, improves creativity by priming associative networks," by Denise J. Cai, Sarnoff A. Mednick, Elizabeth M. Harrison, Jennifer Kanady, and Sara C. Mednick

MEDIA CONTACT: Sara Mednick, Department of Psychiatry, University of California at San Diego, La Jolla, CA; tel: 858-552-8585, x2895; e-mail: smednick@ucsd.edu

A genetic mutation previously known only for its statistical link to gout may be responsible for a defect in a cellular uric acid transporter that leads to the condition.

Article #09-01249: "Identification of an urate transporter, ABCG2, with a common functional polymorphism causing gout," by Owen M. Woodward, Anna Köttgen, Josef Coresh, Eric Boerwinkle, William B. Guggino, and Michael Köttgen

MEDIA CONTACT: Michael Köttgen, Johns Hopkins School of Medicine, Baltimore, MD; tel: 410-955-6281; e-mail: koettgen@jhmi.edu