Spider capture silk: performance implications of variation in an exceptional biomaterial

Spiders and their silk are an excellent system for connecting the properties of biological materials to organismal ecology. Orb-weaving spiders spin sticky capture threads that are moderately strong but exceptionally extensible, resulting in fibers that can absorb remarkable amounts of energy. These tough fibers are thought to be adapted for arresting flying insects. Using tensile testing, we ask whether patterns can be discerned in the evolution of silk material properties and the ecological uses of spider capture fibers. Here, we present a large comparative data set that allows examination of capture silk properties across orb-weaving spider species. We find that material properties vary greatly across species. Notably, extensibility, strength, and toughness all vary approximately sixfold across species. These material differences, along with variation in fiber size, dictate that the mechanical performance of capture threads, the energy and force required to break fibers, varies by more than an order of magnitude across species. Furthermore, some material and mechanical properties are evolutionarily correlated. For example, species that spin small diameter fibers tend to have tougher silk, suggesting compensation to maintain breaking energy. There is also a negative correlation between strength and extensibility across species, indicating a potential evolutionary trade-off. The different properties of these capture silks should lead to differences in the performance of orb webs during prey capture and help to define feeding niches in spiders.     

Ten months of exercise improves general and visceral adiposity, bone, and fitness in black girls

Objective: The goal of this study was to evaluate the impact of a 10‐month after‐school physical activity (PA) program on body composition and cardiovascular (CV) fitness in young black girls. Research Methods and Procedures: Subjects were 8‐ to 12‐year‐olds recruited from elementary schools. Body composition was measured using anthropometrics {waist circumference and BMI, DXA [percentage body fat (%BF)] and bone mineral density (BMD)}, and magnetic resonance imaging [visceral adipose tissue (VAT)]. CV fitness was measured using a graded treadmill test. The intervention consisted of 30 minutes homework/healthy snack time and 80 minutes PA (i.e., 25 minutes skills instruction, 35 minutes aerobic PA, and 20 minutes strengthening/stretching). Analyses were adjusted for age, baseline value of the dependent variable, and sexual maturation (pediatrician observation). Results: Mean attendance was 54%. Compared with the control group, the intervention group had a relative decrease in %BF (p < 0.0001), BMI (p < 0.01), and VAT (p < 0.01) and a relative increase in BMD (p < 0.0001) and CV fitness (p < 0.05). Higher attendance was associated with greater increases in BMD (p < 0.05) and greater decreases in %BF (p < 0.01) and BMI (p < 0.05). Higher heart rate during PA was associated with greater increases in BMD (p < 0.05) and greater decreases in %BF (p < 0.005). Discussion: An after‐school PA program can lead to beneficial changes in body composition and CV fitness in young black girls. It is noteworthy that the control and intervention groups differed in change in VAT but not waist circumference. This suggests that changes in central adiposity can occur in response to PA, even in young children, but that waist circumference may not be a good indicator of central adiposity.     

Evolution and ecology of feeding in elasmobranchs

Paleozoic chondrichthyans had a large gape, numerous spike-liketeeth, limited cranial kinesis, and a non-suspensory hyoid,suggesting a feeding mechanism dominated by bite and ram. Modernsharks are characterized by a mobile upper jaw braced by a suspensoryhyoid arch that is highly kinetic. In batoids, the upper jawis dissociated from the cranium permitting extensive protrusionof the jaws. Similar to actinopterygians, the evolution of highlymobile mandibular and hyoid elements has been correlated withextensive radiation of feeding modes in elasmobranchs, particularlythat of suction. Modern elasmobranchs possess a remarkable varietyof feeding modes for a group containing so few species. Biting,suction or filter-feeding may be used in conjunction with ramto capture prey, with most species able to use a combinationof behaviors during a strike. Suction-feeding has repeatedlyarisen within all recent major elasmobranch clades and is associatedwith a suite of morphological and behavioral specializations.Prey capture in a diverse assemblage of purported suction-feedingelasmobranchs is investigated in this study. Drop in water pressuremeasured in the mouth and at the location of the prey showsthat suction inflow drops off rapidly with distance from thepredator's mouth. Elasmobranchs specializing in suction-feedingmay be limited to bottom associated prey and because of theirsmall gape may have a diet restricted to relatively small prey.Behavior can affect performance and overcome constraints imposedby the fluid medium. Suction performance can be enhanced byproximity to a substrate or by decreasing distance from predatorto prey using various morphological and/or behavioral characteristics.Benthic suction-feeders benefit by the increased strike radiusdue to deflection of water flow when feeding close to a substrate,and perhaps require less accuracy when capturing prey. Suctionand ram-suction-feeding elasmobranchs can also use suction inflowto draw prey to them from a short distance, while ram-feedingsharks must accelerate and overtake the prey. The relationshipbetween feeding strategy and ecology may depend in part on ecological,mechanistic or evolutionary specialization. Mechanistic suction-feedingspecialist elasmobranchs are primarily benthic, while most epibenthicand pelagic elasmobranchs are generalists and use ram, suction,and biting to catch a diversity of prey in various habitats.Some shark species are considered to be ecological specialistsin choosing certain kinds of prey over others. Batoids are evolutionaryspecialists in having a flattened morphology and most are generalistfeeders. Filter-feeding elasmobranchs are ecological, mechanistic,and evolutionary specialists.     

In situ proteolysis for protein crystallization and structure determination

We tested the general applicability of in situ proteolysis to form protein crystals suitable for structure determination by adding a protease (chymotrypsin or trypsin) digestion step to crystallization trials of 55 bacterial and 14 human proteins that had proven recalcitrant to our best efforts at crystallization or structure determination. This is a work in progress; so far we determined structures of 9 bacterial proteins and the human aminoimidazole ribonucleotide synthetase (AIRS) domain.     

Short-term variability of airway caliber-a marker of asthma?

Variability in airway caliber is a characteristic feature of asthma. Previous studies reported that the variability in respiratory system impedance (Zrs), measured by the forced oscillation technique during several minutes of tidal breathing, is increased in asthma and may be a marker of inherent instability of the airways. The aims of this study were to determine if short-term variability in impedance correlates with peak expiratory flow (PEF) variability or airway hyperresponsiveness (AHR). The SD of log-transformed impedance (lnZrsSD) was measured as a marker of short-term variability and compared with the diurnal variability of PEF over 2 wk in 28 asthmatic and 7 nonasthmatic subjects and with AHR to histamine in a cohort of 17 asthmatic and 82 nonasthmatic subjects. In addition, lnZrsSD was measured in eight nonasthmatic subjects before and after methacholine challenge in the upright and supine positions. There were no significant differences in lnZrsSD between asthmatic and nonasthmatic subjects (P = 0.68). Furthermore, in asthmatic subjects, lnZrsSD did not correlate with diurnal variability of PEF (rs = -0.12 P = 0.54) or with AHR to histamine (r = 0.10, P = 0.71). Neither methacholine challenge nor supine posture caused any significant change in lnZrsSD. We conclude that our findings do not support previous reports about the utility of short-term variability of impedance. Our findings suggest that, using standard methods for forced oscillometry, impedance variability does not provide clinically useful information about the severity of asthma.     

Advancing the use of morphometric data for estimating and managing common bottlenose dolphin (Tursiops truncatus) mass

Knowledge of a dolphin's body mass is central to establishing body condition, comparing across individuals, and designing successful management programs. In the present study, sex‐specific prediction equations for estimating body mass were generated from morphometrics (i.e., length and girth) and ages of bottlenose dolphins residing under professionally managed care. Measurements of wild dolphins in Sarasota Bay, Florida, were used to generate sex‐specific body mass reference ranges. Gompertz growth models were fitted to length measurements and age to compare growth across populations. From the regression analyses, the body mass of managed females (R² = 0.937), managed males (R² = 0.953), wild females (R² = 0.979), and wild males (R² = 0.972) were predicted with high levels of accuracy. Managed adults had similar or longer asymptotic lengths compared to their wild conspecifics. To apply this information, ZooMorphTrak, a mobile software application, was developed to provide a new resource for management. The “Approximate” feature was designed to approximate body mass based on user inputs of individual morphometrics. The “Management” feature compared a managed dolphin's known body mass with respect to body mass reference ranges generated from wild dolphins. ZooMorphTrak, developed by the Chicago Zoological Society, is available for download at http://itunes.apple.com .     

A fault detection service for wide area distributed computations

The potential for faults in distributed computing systems is a significant complicating factor for application developers. While a variety of techniques exist for detecting and correcting faults, the implementation of these techniques in a particular context can be difficult. Hence, we propose a fault detection service designed to be incorporated, in a modular fashion, into distributed computing systems, tools, or applications. This service uses well-known techniques based on unreliable fault detectors to detect and report component failure, while allowing the user to trade off timeliness of reporting against false positive rates. We describe the architecture of this service, report on experimental results that quantify its cost and accuracy, and describe its use in two applications, monitoring the status of system components of the GUSTO computational grid testbed and as part of the NetSolve network-enabled numerical solver. This revised version was published online in July 2006 with corrections to the Cover Date.     

To strengthen consensus, consult the stakeholders

CIOMS has been criticised for not adequately consulting stakeholders about its revised ethical guidelines regarding medical research. Political and logistical issues that arise in democratic processes and open exchange of information probably contributed to this exclusion. What might CIOMS have done to be more inclusive and attain broader consensus on its proposed revisions? Consensus is dynamic, and evolves as a community digests new information and perspectives. Engaging the public (and particularly the stakeholders) in discussion about the revisions would have generated broader consensus. It would have encouraged more stakeholders (i.e. researchers, potential research participants, research institutions, or governments) to buy in. CIOMS needs a process to encourage dialogue and stakeholder input. The CIOMS guidelines themselves promote stakeholder consultation and capacity building, but CIOMS has done relatively little to distribute or promote its own guidelines. CIOMS should do more to promote its revised guidelines, and engage stakeholders in dialogue. This paper explores the bioethics debate about universal and relative values to illustrate the value of consultation and consensus building. It concludes that like research sponsors, CIOMS and similar organisations have an ethical responsibility to facilitate capacity building in less developed areas, and to participate more actively in consensus building.     

Genomewide linkage searches for Mendelian disease loci can be efficiently conducted using high-density SNP genotyping arrays

Genomewide linkage searches aimed at identifying disease susceptibility loci are generally conducted using 300–400 microsatellite markers. Genotyping bi-allelic single nucleotide polymorphisms (SNPs) provides an alternative strategy. The availability of dense SNP maps coupled with recent technological developments in highly paralleled SNP genotyping makes it practical to now consider the use of these markers for whole-genome genetic linkage analyses. Here, we report the findings from three successful genomewide linkage analyses of families segregating autosomal recessively inherited neonatal diabetes, craniosynostosis and dominantly inherited renal dysplasia using the Affymetrix 10K SNP array. A single locus was identified for each disease state, two of which are novel. The performance of the SNP array, both in terms of efficiency and precision, indicates that such platforms will become the dominant technology for performing genomewide linkage searches.