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10619495

10.1016/J.ZOOL.2008.11.003

Supercontraction forces in spider dragline silk depend on hydration rate.

Spider dragline silk is a model biological polymer for biomimetic research due to its many desirable and unusual properties. 'Supercontraction' describes the dramatic shrinking of dragline silk fibers when wetted. In restrained silk fibers, supercontraction generates substantial stresses of 40-50 MPa above a critical humidity of approximately 70% relative humidity (RH). This stress may maintain tension in webs under the weight of rain or dew and could be used in industry for robotics, sensor technology, and other applications. Our own findings indicate that supercontraction can generate stress over a much broader range than previously reported, from 10 to 140 MPa. Here we show that this variation in supercontraction stress depends upon the rate at which the environment reaches the critical level of humidity causing supercontraction. Slow humidity increase, over several minutes, leads to relatively low supercontraction stress, while fast humidity increase, over a few seconds, typically results in higher supercontraction stress. Slowly supercontracted fibers take up less water and differ in thermostability from rapidly supercontracted fibers, as shown by thermogravimetric analysis. This suggests that spider silk achieves different molecular configurations depending upon the speed at which supercontraction occurs. Ultimately, rate-dependent supercontraction may provide a mechanism to tailor the properties of silk or biomimetic fibers for various applications.

Zoology

86480892

10.1139/Z75-073

Walrus ethology. I. The social role of tusks and applications of multidimensional scaling

Social behavior of male Pacific walruses. Odobenus rosmarus (L.), summering (i.e. outside the breeding season) on an Alaskan hauling ground is described. Social interaction on land is mostly agonistic. Visual presentation of tusks and striking with tusks feature prominently in most agonistic interactions: vocal communication occurs in a minority of them. Agonistic interactions are analyzed in R- and Q-approaches with MIN1SSA, a fully non-metric multidimensional scaling procedure programmed in the Guttman-Lingoes series. Large body size and long tusks characterize dominant walruses. Dominants are most frequently aggressive and threatening, and least frequently exhibit submissive, defensive, protective, and avoidance behavior. Subordinate walruses show the opposite trend. Walruses are bullies; individuals strongly disadvantaged in body size or tusk length, or both, receive numerous strikes and visual threats. Walruses tend to initiate agonistic interactions with smaller individuals. Walrus tusks are importa...

Canadian Journal of Zoology

205244267

10.1073/PNAS.0902466106

Remarkable resilience of teeth

Tooth enamel is inherently weak, with fracture toughness comparable with glass, yet it is remarkably resilient, surviving millions of functional contacts over a lifetime. We propose a microstructural mechanism of damage resistance, based on observations from ex situ loading of human and sea otter molars (teeth with strikingly similar structural features). Section views of the enamel implicate tufts, hypomineralized crack-like defects at the enamel–dentin junction, as primary fracture sources. We report a stabilization in the evolution of these defects, by “stress shielding” from neighbors, by inhibition of ensuing crack extension from prism interweaving (decussation), and by self-healing. These factors, coupled with the capacity of the tooth configuration to limit the generation of tensile stresses in largely compressive biting, explain how teeth may absorb considerable damage over time without catastrophic failure, an outcome with strong implications concerning the adaptation of animal species to diet.

Proceedings of the National Academy of Sciences of the United States of America

37739061

10.1103/PHYSREVE.82.011910

Mosquito proboscis: an elegant biomicroelectromechanical system.

The mouthparts of female mosquitoes have evolved to form a special proboscis, a natural biomicroelectromechanical system (BMEMS), which is used for painlessly penetrating human skin and sucking blood. Scanning electron microscope observations show that the mosquito proboscis consists of a small bundle of long, tapering, and feeding stylets that are collectively called the fascicle, and a large scaly outer lower lip called the labium. During blood feeding, only the fascicle penetrates into the skin while the labium buckles back to remain on the surface of the skin. Here, we measured the dynamic force of penetration of the fascicle into human skin to reveal the mechanical principle underlying the painless process of penetration. High-speed video observations of movements associated with insertion of the fascicle indicate that the "smart" mosquito does not directly pierce its victim's skin with the fascicle. Instead, it uses the two maxillas as variable frequency microsaws with nanosharp teeth to advance into the skin tissue. This elegant BMEMS enables the mosquito to insert its feeding fascicle into human skin using an exceedingly small force (average of 16.5 μN).

Physical Review E

9671702

10.1016/J.CELL.2009.07.046

Architecture-Dependent Noise Discriminates Functionally Analogous Differentiation Circuits

Gene regulatory circuits with different architectures (patterns of regulatory interactions) can generate similar dynamics. This raises the question of why a particular circuit architecture is selected to implement a given cellular process. To investigate this problem, we compared the Bacillus subtilis circuit that regulates differentiation into the competence state to an engineered circuit with an alternative architecture (SynEx) in silico and in vivo. Time-lapse microscopy measurements showed that SynEx cells generated competence dynamics similar to native cells and reconstituted the physiology of differentiation. However, architectural differences between the circuits altered the dynamic distribution of stochastic fluctuations (noise) during circuit operation. This distinction in noise causes functional differences between the circuits by selectively controlling the timing of competence episodes and response of the system to various DNA concentrations. These results reveal a tradeoff between temporal precision and physiological response range that is controlled by distinct noise characteristics of alternative circuit architectures.

Cell

207795751

10.1073/PNAS.1919607117

Nonuniform growth and surface friction determine bacterial biofilm morphology on soft substrates

Significance Shape transformations during an organism’s development often arise from mechanical instabilities driven by nonuniform growth. A remarkable example is the formation of 3D wrinkles in bacterial biofilms growing on soft substrates, which may enhance the availability of nutrients and signaling molecules. To investigate the formation of biofilm wrinkle patterns, we developed a chemomechanical model that incorporates nutrient-limited inhomogeneous growth, surface friction, and the ensuing mechanical stresses and deformations. We predict the spatiotemporal stress field in a growing biofilm and how it dictates the formation of 3D biofilm morphology. Our model provides insight into the observed stages of expansion of Vibrio cholerae biofilms and suggests that universal mechanical principles may underlie the formation of 3D morphologies in biofilms across species. During development, organisms acquire three-dimensional (3D) shapes with important physiological consequences. While basic mechanisms underlying morphogenesis are known in eukaryotes, it is often difficult to manipulate them in vivo. To circumvent this issue, here we present a study of developing Vibrio cholerae biofilms grown on agar substrates in which the spatiotemporal morphological patterns were altered by varying the agar concentration. Expanding biofilms are initially flat but later undergo a mechanical instability and become wrinkled. To gain mechanistic insights into this dynamic pattern-formation process, we developed a model that considers diffusion of nutrients and their uptake by bacteria, bacterial growth/biofilm matrix production, mechanical deformation of both the biofilm and the substrate, and the friction between them. Our model shows quantitative agreement with experimental measurements of biofilm expansion dynamics, and it accurately predicts two distinct spatiotemporal patterns observed in the experiments—the wrinkles initially appear either in the peripheral region and propagate inward (soft substrate/low friction) or in the central region and propagate outward (stiff substrate/high friction). Our results, which establish that nonuniform growth and friction are fundamental determinants of stress anisotropy and hence biofilm morphology, are broadly applicable to bacterial biofilms with similar morphologies and also provide insight into how other bacterial biofilms form distinct wrinkle patterns. We discuss the implications of forming undulated biofilm morphologies, which may enhance the availability of nutrients and signaling molecules and serve as a “bet hedging” strategy.

Proceedings of the National Academy of Sciences of the United States of America

29744858

10.1098/RSBL.2005.0307

Spider signals: are web decorations visible to birds and bees?

We are becoming increasingly aware of animal communication outside the range of human sensitivity. Web decorations are silk structures used by orb-web spiders to deceive prey and predators. However, despite the level of interest in these structures, their visibility to prey and predators has never, to our knowledge, been objectively assessed. Here, we use spectrophotometric analyses to show that the decorations of all five tested spider species are visible to honey bees and birds over short and long distances. Furthermore, the discoid decorations of one species may provide some protection against arthropod predators. However, these decorations are inefficient at camouflaging the spider against birds, despite the overlap between the spider's body and web decoration.

Biology Letters

2132139

10.1007/S00359-011-0658-1

Elastic modulus of tree frog adhesive toe pads

Previous work using an atomic force microscope in nanoindenter mode indicated that the outer, 10- to 15-μm thick, keratinised layer of tree frog toe pads has a modulus of elasticity equivalent to silicone rubber (5–15 MPa) (Scholz et al. 2009), but gave no information on the physical properties of deeper structures. In this study, micro-indentation is used to measure the stiffness of whole toe pads of the tree frog, Litoria caerulea. We show here that tree frog toe pads are amongst the softest of biological structures (effective elastic modulus 4–25 kPa), and that they exhibit a gradient of stiffness, being stiffest on the outside. This stiffness gradient results from the presence of a dense network of capillaries lying beneath the pad epidermis, which probably has a shock absorbing function. Additionally, we compare the physical properties (elastic modulus, work of adhesion, pull-off force) of the toe pads of immature and adult frogs.

Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology

21413563

10.1104/PP.60.4.609

Thermal Energy Exchange Model and Water Loss of a Barrel Cactus, Ferocactus acanthodes.

The influences of various diurnal stomatal opening patterns, spines, and ribs on the stem surface temperature and water economy of a CAM succulent, the barrel cactus Ferocactus acanthodes, were examined using an energy budget model. To incorporate energy exchanges by shortwave and longwave irradiation, latent heat, conduction, and convection as well as the heat storage in the massive stem, the plant was subdivided into over 100 internal and external regions in the model. This enabled the average surface temperature to be predicted within 1 C of the measured temperature for both winter and summer days.Reducing the stem water vapor conductance from the values observed in the field to zero caused the average daily stem surface temperature to increase only 0.7 C for a winter day and 0.3 C for a summer day. Thus, latent heat loss does not substantially reduce stem temperature. Although the surface temperatures averaged 18 C warmer for the summer day than for the winter day for a plant 41 cm tall, the temperature dependence of stomatal opening caused the simulated nighttime water loss rates to be about the same for the 2 days.Spines moderated the amplitude of the diurnal temperature changes of the stem surface, since the daily variation was 17 C for the winter day and 25 C for the summer day with spines compared with 23 C and 41 C, respectively, in their simulated absence. Ribs reduced the daytime temperature rise by providing 54% more area for convective heat loss than for a smooth circumscribing surface. In a simulation where both spines and ribs were eliminated, the daytime average surface temperature rose by 5 C.

Plant Physiology

15774150

10.1371/JOURNAL.PONE.0063609

Optimal Predator Risk Assessment by the Sonar-Jamming Arctiine Moth Bertholdia trigona

Nearly all animals face a tradeoff between seeking food and mates and avoiding predation. Optimal escape theory holds that an animal confronted with a predator should only flee when benefits of flight (increased survival) outweigh the costs (energetic costs, lost foraging time, etc.). We propose a model for prey risk assessment based on the predator's stage of attack. Risk level should increase rapidly from when the predator detects the prey to when it commits to the attack. We tested this hypothesis using a predator – the echolocating bat – whose active biosonar reveals its stage of attack. We used a prey defense – clicking used for sonar jamming by the tiger moth Bertholdia trigona– that can be readily studied in the field and laboratory and is enacted simultaneously with evasive flight. We predicted that prey employ defenses soon after being detected and targeted, and that prey defensive thresholds discriminate between legitimate predatory threats and false threats where a nearby prey is attacked. Laboratory and field experiments using playbacks of ultrasound signals and naturally behaving bats, respectively, confirmed our predictions. Moths clicked soon after bats detected and targeted them. Also, B. trigona clicking thresholds closely matched predicted optimal thresholds for discriminating legitimate and false predator threats for bats using search and approach phase echolocation – the period when bats are searching for and assessing prey. To our knowledge, this is the first quantitative study to correlate the sensory stimuli that trigger defensive behaviors with measurements of signals provided by predators during natural attacks in the field. We propose theoretical models for explaining prey risk assessment depending on the availability of cues that reveal a predator's stage of attack.

PLOS ONE

914857

10.1038/NATURE05466

Two chemosensory receptors together mediate carbon dioxide detection in Drosophila

Blood-feeding insects, including the malaria mosquito Anopheles gambiae, use highly specialized and sensitive olfactory systems to locate their hosts. This is accomplished by detecting and following plumes of volatile host emissions, which include carbon dioxide (CO2). CO2 is sensed by a population of olfactory sensory neurons in the maxillary palps of mosquitoes and in the antennae of the more genetically tractable fruitfly, Drosophila melanogaster. The molecular identity of the chemosensory CO2 receptor, however, remains unknown. Here we report that CO2-responsive neurons in Drosophila co-express a pair of chemosensory receptors, Gr21a and Gr63a, at both larval and adult life stages. We identify mosquito homologues of Gr21a and Gr63a, GPRGR22 and GPRGR24, and show that these are co-expressed in A. gambiae maxillary palps. We show that Gr21a and Gr63a together are sufficient for olfactory CO2-chemosensation in Drosophila. Ectopic expression of Gr21a and Gr63a together confers CO2 sensitivity on CO2-insensitive olfactory neurons, but neither gustatory receptor alone has this function. Mutant flies lacking Gr63a lose both electrophysiological and behavioural responses to CO2. Knowledge of the molecular identity of the insect olfactory CO2 receptors may spur the development of novel mosquito control strategies designed to take advantage of this unique and critical olfactory pathway. This in turn could bolster the worldwide fight against malaria and other insect-borne diseases.

Nature

17453426

10.1242/JEB.00663

The aerodynamics of insect flight

SUMMARY The flight of insects has fascinated physicists and biologists for more than a century. Yet, until recently, researchers were unable to rigorously quantify the complex wing motions of flapping insects or measure the forces and flows around their wings. However, recent developments in high-speed videography and tools for computational and mechanical modeling have allowed researchers to make rapid progress in advancing our understanding of insect flight. These mechanical and computational fluid dynamic models, combined with modern flow visualization techniques, have revealed that the fluid dynamic phenomena underlying flapping flight are different from those of non-flapping, 2-D wings on which most previous models were based. In particular, even at high angles of attack, a prominent leading edge vortex remains stably attached on the insect wing and does not shed into an unsteady wake, as would be expected from non-flapping 2-D wings. Its presence greatly enhances the forces generated by the wing, thus enabling insects to hover or maneuver. In addition, flight forces are further enhanced by other mechanisms acting during changes in angle of attack, especially at stroke reversal, the mutual interaction of the two wings at dorsal stroke reversal or wing–wake interactions following stroke reversal. This progress has enabled the development of simple analytical and empirical models that allow us to calculate the instantaneous forces on flapping insect wings more accurately than was previously possible. It also promises to foster new and exciting multi-disciplinary collaborations between physicists who seek to explain the phenomenology, biologists who seek to understand its relevance to insect physiology and evolution, and engineers who are inspired to build micro-robotic insects using these principles. This review covers the basic physical principles underlying flapping flight in insects, results of recent experiments concerning the aerodynamics of insect flight, as well as the different approaches used to model these phenomena.

The Journal of Experimental Biology

12941846

10.1016/J.IJPARA.2010.09.012

No shot in the dark: myxozoans chemically detect fresh fish.

This work reports the discovery of an hitherto unknown chemical recognition trait enabling a parasitic life cycle in aquatic habitats. We believe this is the first record of a natural, host-derived chemical molecule identified as a recognition cue for the phylum Myxozoa. The actinospores of these parasites attach to fish hosts via polar filaments that are extruded upon mechanical stimulation after preceding recognition of a chemical trigger contained in surface mucus. Our goal was to identify this signal. We separated compounds from a purified active fraction derived from trout mucus by a novel HPLC method. By subsequent nuclear magnetic resonance analysis of distinct components and testing in bioassays we elicited stimulation of polar filament discharge and sporoplasm emission in actinospores of three myxozoan spp., Myxobolus cerebralis, Myxobolus pseudodispar and Henneguya nuesslini, by the free nucleosides inosine, 2'-deoxyinosine and guanosine. These nucleosides also activated sporoplasm emission. Nucleosides appear to be appropriate cues for rapid host recognition by the waterborne parasite stages since they are continuously released into surface mucus. The recognition mechanism is not specific for susceptible host species, at least in the myxozoan spp. examined. In addition, a novel function of nucleobase derivatives as semiochemicals was uncovered and a wider impact of this molecule class in parasite recognition systems and aquatic chemical ecology is predicted. The relevance for disease prevention and cell culturing remains to be explored.

International Journal for Parasitology

85008369

10.1007/BF00346343

A study of mucus from the solitary coral Fungia fungites (Scleractinia: Fungiidae) in relation to photobiological UV adaptation

The ultraviolet (UV)-absorbance spectrum (300 to 360 nm) of mucus obtained from Fungia fungites (L. 1758, collected in Tahiti in 1991) after being exposed to air for up to 5 min was measured, and UV-absorbing compounds were demonstrated to be present in the mucus, with a peak at 332 nm. The concentration of these UV-absorbing compounds was at a maximum in the first 2 min of secretion and decreased thereafter. Concentration was significantly related to the weight of the coral. Also, as corals were adapted to bathymetric levels of UV radiation, mucus concentration of UV-absorbing compounds decreased significantly with increasing depth.

Marine Biology

23500477

10.1126/SCIENCE.1088295

Fish Exploiting Vortices Decrease Muscle Activity

Fishes moving through turbulent flows or in formation are regularly exposed to vortices. Although animals living in fluid environments commonly capture energy from vortices, experimental data on the hydrodynamics and neural control of interactions between fish and vortices are lacking. We used quantitative flow visualization and electromyography to show that trout will adopt a novel mode of locomotion to slalom in between experimentally generated vortices by activating only their anterior axial muscles. Reduced muscle activity during vortex exploitation compared with the activity of fishes engaged in undulatory swimming suggests a decrease in the cost of locomotion and provides a mechanism to understand the patterns of fish distributions in schools and riverine environments.

Science

7001585

10.1007/S00223-014-9915-Y

Skeletal Muscle: A Brief Review of Structure and Function

Abstract Skeletal muscle is one of the most dynamic and plastic tissues of the human body. In humans, skeletal muscle comprises approximately 40 % of total body weight and contains 50–75 % of all body proteins. In general, muscle mass depends on the balance between protein synthesis and degradation and both processes are sensitive to factors such as nutritional status, hormonal balance, physical activity/exercise, and injury or disease, among others. In this review, we discuss the various domains of muscle structure and function including its cytoskeletal architecture, excitation-contraction coupling, energy metabolism, and force and power generation. We will limit the discussion to human skeletal muscle and emphasize recent scientific literature on single muscle fibers.

Calcified Tissue International

22426029

10.1023/A:1023334628751

Tropic failure of Phyllactinia corylea contributes to the mildew resistance of mulberry genotypes

Different mulberry genotypes show great variation in their resistance to the powdery mildew Phyllactinia corylea. Conidial germination and hyphal growth of P. corylea on the leaf surface of two susceptible mulberry genotypes, viz., Kanva 2 (K2) and Victory 1 (V1) varieties of Morus indica, and on two resistant species, viz., M. laevigata and M. serrata were studied by scanning electron microscopy. Conidial germination and growth of germ tubes were normal on all the leaves. The hyphae of P. coryleaidentify stomata on host leaves by their topographical features to produce the stomatopodia precisely over them. The holes and/or the grooves of stomata appear to provide the signals for the initiation of stomatopodia and similar structures are erratically developed over many local depressions or grooves on leaf surface. The abaxial surface of K2 leaf is smooth without prominent undulations of epidermal cell surface, and the stomata are flush with the leaf surface. Although successful penetration is also achieved on V1 leaf, its slightly undulated surface occasionally provides inaccurate tropic signals to the hyphae, inducing the development of stomatopodia away from the stomata. The leaf surfaces of M. laevigata and M. serrata are very rough with highly sculptured cuticle and abundant epidermal outgrowths. Stomata mostly remain sunken or hidden amidst the cuticular ornamentations and the hyphae fail to recognise the precise signals from them. As the surface architecture of the leaves provides many immense sources of tropic signals, stomatopodia are often produced over local depressions or grooves. In these cases the fungus fails to penetrate the leaf, does not develop beyond 24 h and penetration is rarely achieved on the leaves of the resistant plants. The study indicates that the stimulatory effect of the leaf surface topography of resistant varieties misleads the pathogen from successful penetration, thus contributing to the plant's resistance.

Mycopathologia

59444003

10.1063/1.3515563

Correlating Nanostructures with Function: Structural Colors on the Wings of a Malaysian Bee

Structural colours refer to colours generated by nanostructures, with the characteristic dimension of the structures on the wavelength of the visible light (i.e., some hundreds of nanometers). Examples for structural colours are the colours of CDs and DVDs, the colours of soap bubbles or oil films on water (thin films), or the colours of certain butterfly wings (e.g., photonic crystals). Recently, we located a Malaysian bee with iridescent structural coloration on its wings. The generation of the colouration is still unknown, and there is no respective scientific literature available. This study presents the first AFM experiments related to the structural coloration of the carpenter bee wing. First attempts to investigate the nanostructures of the wing were performed with non‐contact atomic force microscopy (AFM, Park Systems XE‐100), using a Silicon nitride cantilever with a spring constant of 40 N/m and a resonance frequency of 300.000 kHz. The AFM scans reveal three layers with structures with a diamet...

THE THIRD NANOSCIENCE AND NANOTECHNOLOGY SYMPOSIUM 2010 (NNSB2010)

23826789

10.1098/RSPB.2017.0347

Sneeze to leave: African wild dogs (Lycaon pictus) use variable quorum thresholds facilitated by sneezes in collective decisions

In despotically driven animal societies, one or a few individuals tend to have a disproportionate influence on group decision-making and actions. However, global communication allows each group member to assess the relative strength of preferences for different options among their group-mates. Here, we investigate collective decisions by free-ranging African wild dog packs in Botswana. African wild dogs exhibit dominant-directed group living and take part in stereotyped social rallies: high energy greeting ceremonies that occur before collective movements. Not all rallies result in collective movements, for reasons that are not well understood. We show that the probability of rally success (i.e. group departure) is predicted by a minimum number of audible rapid nasal exhalations (sneezes), within the rally. Moreover, the number of sneezes needed for the group to depart (i.e. the quorum) was reduced whenever dominant individuals initiated rallies, suggesting that dominant participation increases the likelihood of a rally's success, but is not a prerequisite. As such, the ‘will of the group’ may override dominant preferences when the consensus of subordinates is sufficiently great. Our findings illustrate how specific behavioural mechanisms (here, sneezing) allow for negotiation (in effect, voting) that shapes decision-making in a wild, socially complex animal society.

Proceedings of The Royal Society B: Biological Sciences

138117551

10.1007/BF03399449

Dynamics of Drying in Phenolically Tanned Materials

The cuticle of a maggot goes through a mechanical transition when it dries, increasing in stiffness by about an order of magnitude (e.g. from 0.5 GPa to 5 GPa) as the water content drops from about 1 g/g (weight of water per unit dry weight) to 0.4 g/g. Thus stiffness represents the loss of freezable water and is more or less diagnostic of a material stabilized by hydrogen bonds. Further loss in water results in a smaller increase in stiffness. In natural systems the water content is controlled by the addition of phenolic residues, resulting in tanning or sclerotisation, which drives the matrix components towards co-operative interaction and makes the material permanently waterproof.

Journal of Bionic Engineering

37236982

10.1016/J.CHEMOSPHERE.2012.09.045

Plant-bacteria partnerships for the remediation of hydrocarbon contaminated soils.

Plant-bacteria partnerships have been extensively studied and applied to improve crop yield. In addition to their application in agriculture, a promising field to exploit plant-bacteria partnerships is the remediation of soil and water polluted with hydrocarbons. Application of effective plant-bacteria partnerships for the remediation of hydrocarbons depend mainly on the presence and metabolic activities of plant associated rhizo- and endophytic bacteria possessing specific genes required for the degradation of hydrocarbon pollutants. Plants and their associated bacteria interact with each other whereby plant supplies the bacteria with a special carbon source that stimulates the bacteria to degrade organic contaminants in the soil. In return, plant associated-bacteria can support their host plant to overcome contaminated-induced stress responses, and improve plant growth and development. In addition, plants further get benefits from their associated-bacteria possessing hydrocarbon-degradation potential, leading to enhanced hydrocarbon mineralization and lowering of both phytotoxicity and evapotranspiration of volatile hydrocarbons. A better understanding of plant-bacteria partnerships could be exploited to enhance the remediation of hydrocarbon contaminated soils in conjunction with sustainable production of non-food crops for biomass and biofuel production.

Chemosphere

31381395

10.1126/SCIENCE.289.5487.2114

How snapping shrimp snap: through cavitating bubbles.

The snapping shrimp (Alpheus heterochaelis) produces a loud snapping sound by an extremely rapid closure of its snapper claw. One of the effects of the snapping is to stun or kill prey animals. During the rapid snapper claw closure, a high-velocity water jet is emitted from the claw with a speed exceeding cavitation conditions. Hydrophone measurements in conjunction with time-controlled high-speed imaging of the claw closure demonstrate that the sound is emitted at the cavitation bubble collapse and not on claw closure. A model for the bubble dynamics based on a Rayleigh-Plesset-type equation quantitatively accounts for the time dependence of the bubble radius and for the emitted sound.

Science

1587591

10.1098/RSPB.2012.1297

Underwater locomotion in a terrestrial beetle: combination of surface de-wetting and capillary forces

For the first time, we report the remarkable ability of the terrestrial leaf beetle Gastrophysa viridula to walk on solid substrates under water. These beetles have adhesive setae on their feet that produce a secretory fluid having a crucial role in adhesion on land. In air, adhesion is produced by capillary forces between the fluid-covered setae and the substrate. In general, capillary forces do not contribute to adhesion under water. However, our observations showed that these beetles may use air bubbles trapped between their adhesive setae to walk on flooded, inclined substrata or even under water. Beetle adhesion to hydrophilic surfaces under water was lower than that in air, whereas adhesion to hydrophobic surfaces under water was comparable to that in air. Oil-covered hairy pads had a pinning effect, retaining the air bubbles on their feet. Bubbles in contact with the hydrophobic substrate de-wetted the substrate and produced capillary adhesion. Additional capillary forces are generated by the pad's liquid bridges between the foot and the substrate. Inspired by this idea, we designed an artificial silicone polymer structure with underwater adhesive properties.

Proceedings of The Royal Society B: Biological Sciences

7472138

10.1016/J.JSB.2006.10.027

Hierarchical assembly of the siliceous skeletal lattice of the hexactinellid sponge Euplectella aspergillum.

Despite its inherent mechanical fragility, silica is widely used as a skeletal material in a great diversity of organisms ranging from diatoms and radiolaria to sponges and higher plants. In addition to their micro- and nanoscale structural regularity, many of these hard tissues form complex hierarchically ordered composites. One such example is found in the siliceous skeletal system of the Western Pacific hexactinellid sponge, Euplectella aspergillum. In this species, the skeleton comprises an elaborate cylindrical lattice-like structure with at least six hierarchical levels spanning the length scale from nanometers to centimeters. The basic building blocks are laminated skeletal elements (spicules) that consist of a central proteinaceous axial filament surrounded by alternating concentric domains of consolidated silica nanoparticles and organic interlayers. Two intersecting grids of non-planar cruciform spicules define a locally quadrate, globally cylindrical skeletal lattice that provides the framework onto which other skeletal constituents are deposited. The grids are supported by bundles of spicules that form vertical, horizontal and diagonally ordered struts. The overall cylindrical lattice is capped at its upper end by a terminal sieve plate and rooted into the sea floor at its base by a flexible cluster of barbed fibrillar anchor spicules. External diagonally oriented spiral ridges that extend perpendicular to the surface further strengthen the lattice. A secondarily deposited laminated silica matrix that cements the structure together additionally reinforces the resulting skeletal mass. The mechanical consequences of each of these various levels of structural complexity are discussed.

Journal of Structural Biology

85771615

10.1642/0004-8038(2007)124[1244:SPFAOS]2.0.CO;2

SMALL-PREY PROFITABILITY: FIELD ANALYSIS OF SHOREBIRDS’ USE OF SURFACE TENSION OF WATER TO TRANSPORT PREY

Abstract Previous laboratory studies have shown that Red-necked Phalarope (Phalaropus lobatus), Wilson’s Phalarope (P. tricolor), Western Sandpiper (Calidris mauri), and Least Sandpiper (C. minutilla) use the surface tension of water surrounding a prey item to transport it from bill tip to mouth. Although such experimental work suggests that many species of shorebird may be capable of surface-tension feeding, no field studies have been done that examine this possibility. We studied the occurrence and interspecific variation in the performance of surface-tension transport (STT) in wild shorebirds feeding on identical prey items in shallow water. All shorebirds videotaped—Little Stint (C. minuta), Dunlin (C. alpina), Sanderling (C. alba), Curlew Sandpiper (C. ferruginea), Common Redshank (Tringa totanus), and Black-winged Stilt (Himantopus himantopus)—used STT to feed on small prey items. Individuals employing STT used one or several cycles of jaw spreading to transport the prey contained in a drop of water upward along the bill cavity, an action indicative of STT. Two distinct types of prey transport were observed: (1) use of STT in isolation by calidridine species following the description given in previous studies (i.e., an absence of other feeding mechanisms such as tongue movements, suction, or inertial transport), and (2) STT aided by inertial transport (head jerks) as seen in Common Redshank and Black-winged Stilt. Measured prey-transport variables (number of cycles, total time, and speed of transport) varied among species. The absence of significant relationships between these variables and measures of external morphology (bill length, bill length-to-width ratio, and bill length-to-depth ratio) suggests that some interspecific variations in STT performance may be attributable to differences in internal bill morphology. We show that STT is a common feeding mechanism in small or medium- sized shorebird species that feed on small prey items in shallow water. Birds using STT transported ≤3.6× faster than the theoretical value predicted by a previous model and can achieve high intake rates when foraging on high densities of available small prey items. Ventajas de las Presas Pequeñas: Análisis de Campo del Uso de la Tensión Superficial del Agua por las Aves Playeras para Transportar las Presas

The Auk

7404887

10.1098/RSIF.2010.0140

The attachment strategy of English ivy: a complex mechanism acting on several hierarchical levels

English ivy (Hedera helix L.) is able to grow on vertical substrates such as trees, rocks and house plaster, thereby attaching so firmly to the surface that when removed by force typically whole pieces of the climbing substrate are torn off. The structural details of the attachment process are not yet entirely understood. We studied the attachment process of English ivy in detail and suggest a four-phase process to describe the attachment strategy: (i) initial physical contact, (ii) form closure of the root with the substrate, (iii) chemical adhesion, and (iv) shape changes of the root hairs and form-closure with the substrate. These four phases and their variations play an important role in the attachment to differently structured surfaces. We demonstrate that, in English ivy, different mechanisms work together to allow the plant's attachment to various climbing substrates and reveal the importance of micro-fibril orientation in the root hairs for the attachment based on structural changes at the subcellular level.

Journal of the Royal Society Interface

13256089

10.1371/JOURNAL.PBIO.1000257

Structural Basis for the Aminoacid Composition of Proteins from Halophilic Archea

In order to survive in highly saline environments, proteins from halophilic archea have evolved with biased amino acid compositions that have the capacity to reduce contacts with the solvent.

PLOS Biology

30210834

10.1038/NCHEMBIO.2007.5

The function of terpene natural products in the natural world.

As the largest class of natural products, terpenes have a variety of roles in mediating antagonistic and beneficial interactions among organisms. They defend many species of plants, animals and microorganisms against predators, pathogens and competitors, and they are involved in conveying messages to conspecifics and mutualists regarding the presence of food, mates and enemies. Despite the diversity of terpenes known, it is striking how phylogenetically distant organisms have come to use similar structures for common purposes. New natural roles undoubtedly remain to be discovered for this large class of compounds, given that such a small percentage of terpenes has been investigated so far.

Nature Chemical Biology

17667314

10.1242/JEB.01559

The ontogenetic changes in the thermal properties of blubber from Atlantic bottlenose dolphin Tursiops truncatus

SUMMARY In Atlantic bottlenose dolphins Tursiops truncatus, both the thickness and lipid content of blubber vary across ontogeny and across individuals of differing reproductive and nutritional status. This study investigates how these changes in blubber morphology and composition influence its thermal properties. Thermal conductivity (W m–1 deg.–1, where deg. is °C) and thermal insulation (m2 deg. W–1) of dolphin blubber were measured in individuals across an ontogenetic series (fetus through adult, N=36), pregnant females (N=4) and emaciated animals (N=5). These thermal properties were determined by the simultaneous use of two common experimental approaches, the heat flux disc method and the standard material method. Thickness, lipid and water content were measured for each blubber sample. Thermal conductivity and insulation varied significantly across ontogeny. Blubber from fetuses through sub-adults was less conductive (range=0.11–0.13±0.02 W m–1 deg.–1) than that of adults (mean=0.18 W m–1 deg.–1). The conductivity of blubber from pregnant females was similar to non-adult categories, while that of emaciated animals was significantly higher (0.24 ± 0.04 W m deg.–1) than all other categories. Blubber from sub-adults and pregnant females had the highest insulation values while fetuses and emaciated animals had the lowest. In nutritionally dependant life history categories, changes in blubber's thermal insulation were characterized by stable blubber quality (i.e. conductivity) and increased blubber quantity (i.e. thickness). In nutritionally independent animals, blubber quantity remained stable while blubber quality varied. A final, unexpected observation was that heat flux measurements at the deep blubber surface were significantly higher than that at the superficial surface, a pattern not observed in control materials. This apparent ability to absorb heat, coupled with blubber's fatty acid composition, suggest that dolphin integument may function as a phase change material.

The Journal of Experimental Biology

13865546

10.1038/NATURE05678

Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems

Photosynthetic complexes are exquisitely tuned to capture solar light efficiently, and then transmit the excitation energy to reaction centres, where long term energy storage is initiated. The energy transfer mechanism is often described by semiclassical models that invoke ‘hopping’ of excited-state populations along discrete energy levels. Two-dimensional Fourier transform electronic spectroscopy has mapped these energy levels and their coupling in the Fenna–Matthews–Olson (FMO) bacteriochlorophyll complex, which is found in green sulphur bacteria and acts as an energy ‘wire’ connecting a large peripheral light-harvesting antenna, the chlorosome, to the reaction centre. The spectroscopic data clearly document the dependence of the dominant energy transport pathways on the spatial properties of the excited-state wavefunctions of the whole bacteriochlorophyll complex. But the intricate dynamics of quantum coherence, which has no classical analogue, was largely neglected in the analyses—even though electronic energy transfer involving oscillatory populations of donors and acceptors was first discussed more than 70 years ago, and electronic quantum beats arising from quantum coherence in photosynthetic complexes have been predicted and indirectly observed. Here we extend previous two-dimensional electronic spectroscopy investigations of the FMO bacteriochlorophyll complex, and obtain direct evidence for remarkably long-lived electronic quantum coherence playing an important part in energy transfer processes within this system. The quantum coherence manifests itself in characteristic, directly observable quantum beating signals among the excitons within the Chlorobium tepidum FMO complex at 77 K. This wavelike characteristic of the energy transfer within the photosynthetic complex can explain its extreme efficiency, in that it allows the complexes to sample vast areas of phase space to find the most efficient path.

Nature

85211706

10.1006/JARE.1997.0316

Psammophily in Namib Desert spiders

Abstract A community of psammophilous spiders was studied in the central Namib Desert. Of 20 species, 85% were cursorial. Complex setae, claws or keels facilitate digging, sweeping, carrying, and swimming in or walking on sand, while long spigots enable spiders to bind sand with silk when burrowing down to depths with amenable microclimate (10–120 cm). Sand is excavated either by sweeping it up an incline or carrying it vertically up. Other characteristics of dune spiders were large size, polyphagy, low metabolism, longevity, brood care and seasonal foraging and breeding patterns. The large, dominant heteropodid, Leucorchestris , may determine many characteristics of the Namib arthropod community.

Journal of Arid Environments

59063287

10.1088/0022-3727/40/7/050

Unusual coloration in scarabaeid beetles

In this paper we investigate the reflection of circularly polarized light from the exocuticle of the scarabaeid beetle Gymnopleurus virens. Reflection spectra are deeply modulated, exhibiting a number of relatively narrow well-defined peaks, which differ from previously studied specimens. By comparing model calculations and electron microscopy work with the recorded spectra, we can propose the presence of specific structural defects responsible for the unusual spectra.

Journal of Physics D

137063822

10.1016/S1672-6529(07)60006-7

The sandfish’s skin: Morphology, chemistry and reconstruction

The sandfish is a lizard having the remarkable ability to move in desert sand in a swimming-like fashion. The most outstanding adaptations to this mode of life are the low friction behaviour and the extensive abrasion resistance of the sandfish skin against sand, outperforming even steel. We investigated the topography, the composition and the mechanical properties of sandfish scales. These consist of glycosylated keratins with high amount of sulphur but no hard inorganic material, such as silicates or lime. Remarkably, atomic force microscopy shows an almost complete absence of attractive forces between the scale surface and a silicon tip, suggesting that this is responsible for the unusual tribological properties. The unusual glycosylation of the keratins was found to be absolutely necessary for the described phenomenon. The scales were dissolved and reconstituted on a polymer surface resulting in properties similar to the original scale. Thus, we provide a pathway towards exploitation of the reconstituted scale material for future engineering applications.

Journal of Bionic Engineering

88889935

10.1080/00445096.1973.11448511

The Structure of the Water-Holding Feathers of the Namaqua Sandgrouse

The morphology and fine structure of the feather barbules of the Namaqua Sandgrouse Pterocles namaqua are investigated histologically and experimentally by means of light microscopy, scanning electron micrography and X-ray diffraction. Proximally the barbule is helically coiled for three and a half turns and has a kidney-shaped, concave/convex transverse section. The inner concave surface is pitted, the outer convex surface smooth. The barbule is solid, consisting of three layers, and bears a number of appendages at its distal end, where it is more rounded in transverse section. The uncoiling of barbules from the abdominal feathers on contact with water may be initiated by water uptake and further facilitated by the number of helical coils at the base of the barbules. The keratin is fairly crystalline when dry. This crystallinity is somewhat reduced on wetting. The uncoiling mechanism is related to the expansion of the polypeptide chains of Il-keratin in order to accommodate additional water bound to the side chains.

African Zoology

20881473

10.1002/JMOR.1052250105

Hydrodynamic design of the humpback whale flipper

The humpback whale (Megaptera novaeangliae) is reported to use its elongate pectoral flippers during swimming maneuvers. The morphology of the flipper from a 9.02‐m whale was evaluated with regard to this hydrodynamic function. The flipper had a wing‐like, high aspect ratio plan‐form. Rounded tubercles were regularly interspersed along the flipper's leading edge. The flipper was cut into 71 2.5‐cm cross‐sections and photographed. Except for sections near the distal tip, flipper sections were symmetrical with no camber. Flipper sections had a blunt, rounded leading edge and a highly tapered trailing edge. Placement of the maximum thickness placement for each cross‐section varied from 49% of chord at the tip to 19% at mid‐span. Section thickness ratio averaged 0.23 with a range of 0.20–0.28. The humpback whale flipper had a cross‐sectional design typical of manufactured aerodynamic foils for lift generation. The morphology and placement of leading edge tubercles sugges that they function as enhanced lift devices to control flow over the flipper and maintain lift at high angles of attack. The morphology of the humpback whale flipper suggests that it is adapted for high maneuverability associated with the whale's unique feeding behavior. © 1995 Wiley‐Liss, Inc.

Journal of Morphology

86958396

10.1080/00275514.1998.12026945

Distribution, abundances, and associations of the endophytic fungal community of Arizona fescue (Festuca arizonica)

We documented patterns of species diver- sity, relative abundances, and associations of the fun- gal endophyte community inhabiting Arizona fescue (Festuca arizonica), a dominant perennial bunchgrass in ponderosa pine-grassland communities of the Southwestern USA. We also determined spatial vari- ation in frequency of a vertically-transmitted and asexual fungus, Neotyphodium starrii, a dominant en- dophyte in Arizona fescue. To determine if Neoty- phodium frequency is affected by grazing, we com- pared frequency of infected grasses inside and out- side long-term grazing exclosures in four Arizona fes- cue populations. Likewise, we correlated soil nitrogen levels within and among these four, and an additional, population to determine if the frequency of Neotyphodium-infected plants is related to available soil nutrients. More than 400 different fungi were isolated from Arizona fescue. However, most of these were extremely rare and isolated only once. Neoty- phodium starrii and 13 other morphospecies com- prised the majority of fungal taxa. These results sug- gest that the fungal endophyte communities of pe- rennial grasses may be as diverse as fungal endophyte communities of woody shrubs and trees, despite high infection levels of the asexual and vertically-transmit- ted Neotyphodium. The diversity and dominance of non-Neotyphodium endophytes were highly variable among Arizona fescue populations and varied season- ally and yearly within and among populations. Most of these fungal species are probably opportunistic colonizers that increase in abundance in late summer with seasonal rains that promote spore transmission and germination and hyphal growth. Neotyphodium starrii also varied spatially within and among Arizona fescue populations, although always occurring at higher levels than other endophytic fungi. However, Neotyphodium frequencies were not greater outside grazing exclosures as expected if the endophyte con- fers increased resistance to vertebrate herbivores.

Mycologia

24797238

10.1242/JEB.096909

Spontaneous unraveling of hagfish slime thread skeins is mediated by a seawater-soluble protein adhesive

Hagfishes are known for their ability to rapidly produce vast quantities of slime when provoked. The slime is formed via the interaction between seawater and two components released by the slime glands: mucin vesicles from gland mucous cells, which swell and rupture in seawater to form a network of mucus strands, and intermediate filament-rich threads, which are produced within gland thread cells as tightly coiled bundles called skeins. A previous study showed that the unraveling of skeins from Atlantic hagfish (Myxine glutinosa) requires both the presence of mucins and hydrodynamic mixing. In contrast, skeins from Pacific hagfish (Eptatretus stoutii) unravel in the absence of both mucins and mixing. We tested the hypothesis that spontaneous unraveling of E. stoutii skeins is triggered by the dissolution of a seawater-soluble protein adhesive and the release of stored strain energy within the coiled thread. Here we show that, as predicted by this hypothesis, unraveling can be initiated by a protease under conditions in which unraveling does not normally occur. We also demonstrate, using high resolution scanning electron microscopy, that the treatment of skeins with solutions that cause unraveling also leads to the disappearance of surface and inter-thread features that remain when skeins are washed with stabilizing solutions. Our study provides a mechanism for the deployment of thread skeins in Pacific hagfish slime, and raises the possibility of producing novel biomimetic protein adhesives that are salt, temperature and kosmotrope sensitive.

The Journal of Experimental Biology

1028970

10.1086/657253

Thermoregulation during Flight: Body Temperature and Sensible Heat Transfer in Free-Ranging Brazilian Free-Tailed Bats (Tadarida brasiliensis)

Bat wings are important for thermoregulation, but their role in heat balance during flight is largely unknown. More than 80% of the energy consumed during flight generates heat as a by-product, and thus it is expected that bat wings should dissipate large amounts of heat to prevent hyperthermia. We measured rectal (Tr) and surface (Ts) temperatures of Brazilian free-tailed bats (Tadarida brasiliensis) as they emerged from and returned to their daytime roosts and calculated sensible heat transfer for different body regions (head, body, wings, and tail membrane). Bats’ Tr decreased from 36.8°C during emergence flights to 34.4°C during returns, and Ts scaled positively with ambient temperature (Ta). Total radiative heat loss from bats was significantly greater for a radiative sink to the night sky than for a sink with temperature equal to Ta. We found that free-ranging Brazilian free-tailed bats, on average, do not dissipate heat from their wings by convection but instead dissipate radiative heat (L) to the cloudless night sky during flight ( W). However, within the range of Ta measured in this study, T. brasiliensis experienced net heat loss between evening emergence and return flights. Regional hypothermia reduces heat loss from wings that are exposed to potentially high convective fluxes. Additional research is needed to establish the role of wings in evaporative cooling during flight in bats.

Physiological and Biochemical Zoology

12877489

10.1098/RSIF.2014.0273

Underwater attachment using hairs: the functioning of spatula and sucker setae from male diving beetles

Males of Dytiscinae beetles use specialized adhesive setae to adhere to female elytra during underwater courtship. This coevolution of male setae and female elytra has attracted much attention since Darwin. However, there has been little examination of their biomechanical functioning despite increasing knowledge on biofibrillar adhesion. Here, we report and compare, for the first time, the mechanisms of underwater attachment using two hair types, the primitive spatula and derived ‘passive’ sucker, found in male diving beetles. Results from interspecific scaling of protarsal palettes and adhesion by single seta suggest better performance in the later-evolved circular (sucker) setae. Spatula setae with a modified shallow sucker and channels use the combined mechanisms of suction and viscous resistance for adhesion. Velocity-dependent adhesion provides sufficient control for resisting the female's erratic movements while also detaching easily through slow peeling. Direction-dependent shear resistance helps reorient setae surfaces into a preferred direction for effective adhesion. Seta deformation using different mechanisms for circular and spatula setae reduces the force that is transmitted to the contact interface. A softer spring in spatula setae explains their adhesion at lower preloads and assists in complete substrate contact. Attachment mechanisms revealed in adhesive setae with modified spatula and passive suckers provide insights for bioinspired designs of underwater attachment devices.

Journal of the Royal Society Interface

21884061

10.1103/PHYSREVE.74.051916

Iridescence in the neck feathers of domestic pigeons.

We conducted structural characterizations, reflection measurements, and theoretical simulations on the iridescent green and purple neck feathers of domestic pigeons (Columba livia domestica). We found that both green and purple barbules are composed of an outer keratin cortex layer surrounding a medullary layer. The thickness of the keratin cortex layer shows a distinct difference between green and purple barbules. Green barbules vary colors from green to purple with the observing angle changed from normal to oblique, while purple barbules from purple to green in an opposite way. Both the experimental and theoretical results suggest that structural colors in green and purple neck feathers should originate from the interference in the top keratin cortex layer, while the structure beyond acts as a poor mirror.

Physical Review E

205242361

10.1016/J.ACTBIO.2008.09.011

Comparison of the structure and mechanical properties of bovine femur bone and antler of the North American elk (Cervus elaphus canadensis).

Antler and limb bone have a similar microstructure and chemical composition. Both are primarily composed of type I collagen and a mineral phase (carbonated apatite), arranged in osteons in compact (cortical bone) sections and a lamellar structure in the cancellous (spongy or trabecular bone) sections. The mineral content is lower in antler bone and it has a core of cancellous bone surrounded by compact bone running through the main beam and tines. The mineral content is higher in the compact compared with the cancellous bone, although there is no difference in ratios of the mineral elements with calcium. Mechanical tests (bend and compression) on longitudinal and transverse orientations of dry and rehydrated compact bone of North American elk (Cervus elaphus canadensis) antlers are compared with known data on other antlers as well as bovine femora. Both dry and rehydrated bones are highly anisotropic, with the bending and compressive strength and elastic modulus higher in the longitudinal than in the transverse direction. There is no significant difference between the bend strength and elastic modulus between dry and rehydrated samples tested in the transverse direction. The elastic modulus measured from the bending tests is compared with composite models. The elastic modulus and bend strengths are lower in the rehydrated condition, but the strain to failure and fracture toughness is much higher compared with dry samples. All antler bone mechanical properties are lower than that of bovine femora. The antler has a much higher fracture toughness compared with bovine femora, which correlates with their main function in intraspecific combat as a high impact resistant, energy absorbent material. A model of compression deformation is proposed, which is based on osteon sliding during shear.

Acta Biomaterialia

2450679

10.1126/SCIENCE.1203980

Deciphering the Rhizosphere Microbiome for Disease-Suppressive Bacteria

A common plant pathogen induces the growth of disease-suppressive microbes in local soil communities. Disease-suppressive soils are exceptional ecosystems in which crop plants suffer less from specific soil-borne pathogens than expected owing to the activities of other soil microorganisms. For most disease-suppressive soils, the microbes and mechanisms involved in pathogen control are unknown. By coupling PhyloChip-based metagenomics of the rhizosphere microbiome with culture-dependent functional analyses, we identified key bacterial taxa and genes involved in suppression of a fungal root pathogen. More than 33,000 bacterial and archaeal species were detected, with Proteobacteria, Firmicutes, and Actinobacteria consistently associated with disease suppression. Members of the γ-Proteobacteria were shown to have disease-suppressive activity governed by nonribosomal peptide synthetases. Our data indicate that upon attack by a fungal root pathogen, plants can exploit microbial consortia from soil for protection against infections.

Science

6974569

10.1016/J.MICRON.2007.08.003

Structural analysis of hydrophobins.

Hydrophobins are a remarkable class of small cysteine-rich proteins found exclusively in fungi. They self-assemble to form robust polymeric monolayers that are highly amphipathic and play numerous roles in fungal biology, such as in the formation and dispersal of aerial spores and in pathogenic and mutualistic interactions. The polymeric form can be reversibly disassembled and is able to reverse the wettability of a surface, leading to many proposals for nanotechnological applications over recent years. The surprising properties of hydrophobins and their potential for commercialization have led to substantial efforts to delineate their morphology and molecular structure. In this review, we summarize the progress that has been made using a variety of spectroscopic and microscopic approaches towards understanding the molecular mechanisms underlying hydrophobin structure.

Micron

34594540

10.1016/J.BIORTECH.2010.08.080

CO2 mineralization induced by fungal nitrate assimilation.

Formation of CaCO3 induced by fungal physiological activities is a potential way to sequestrate atmospheric CO2 in ecosystem. Alternaria sp. is a saprophytic fungus isolated from a forest soil. We examined the precipitation of CaCO3 induced by the fungus in response to different levels of Ca(NO3)2 or CaCl2 in agar media, and the biogenesis of CaCO3 was verified by low δ13C value. The formed CaCO3 was identified as calcite by X-ray diffraction analysis. Square, rectangular and rhombic CaCO3 crystals and amorphous calcium carbonate were observed around mycelia at higher levels of Ca(NO3)2. Acidification occurred in media at low concentrations (0 and 0.0002 M) of Ca(NO3)2, and no CaCO3 formed in these media. The quantities of CaCO3 formed in media increased with increasing concentrations of Ca(NO3)2 and were significantly correlated to fungal biomass, pH value and nitrite concentrations. No CaCO3 was formed in media with CaCl2 at all levels. These results collectively indicated that the formation of CaCO3 can be induced by the fungal assimilation of nitrate. The study also revealed that biogenic crystal of CaCO3 tended to grow on a silicon nucleus and the amorphous calcium carbonate (ACC) was the transient stage of CaCO3 crystal.

Bioresource Technology

86038821

10.1080/0028825X.1997.10410160

Explosive flowering, nectar production, breeding systems, and pollinators of New Zealand mistletoes (Loranthaceae)

The six New Zealand loranthaceous mis- tletoes fall into two groups based on pollination bi- ology. Four (Alepis flavida, Peraxilla colensoi, P. tetrapetala, and Trilepidea adamsii) are bird polli- nated with hermaphrodite flowers while the other two (Ileostylus micranthus and Tupeia antarctica) are dioecious or sub-dioecious and insect pollinated. We provide data on the pollination biology of the five extant species (Trilepidea is extinct). The two Peraxilla species and Trilepidea have recently been shown to have explosive flowers. Here we show that Alepis has weakly facultatively explo- sive flowers. The world distribution of explosive mistletoe flowers suggests that the syndrome has arisen a number of times independently within the family, and is found in about half the putatively ancestral genera. The principal avian visitors to the bird-pollinated species were tui and bellbirds; introduced species are numerically unimportant as pollinators. The nectar production schedules of Alepis and Peraxilla encour- age single-visit pollination as little nectar is produced after the flowers open. However, when bird densi- ties are high, buds of Peraxilla may be forced open prematurely, encouraging multiple visits.

New Zealand Journal of Botany

9014819

10.1242/JEB.101931

Wood frog adaptations to overwintering in Alaska: new limits to freezing tolerance

We investigated the ecological physiology and behavior of free-living wood frogs [Lithobates (Rana) sylvaticus] overwintering in Interior Alaska by tracking animals into natural hibernacula, recording microclimate, and determining frog survival in spring. We measured cryoprotectant (glucose) concentrations and identified the presence of antifreeze glycolipids in tissues from subsamples of naturally freezing frogs. We also recorded the behavior of wood frogs preparing to freeze in artificial hibernacula, and tissue glucose concentrations in captive wood frogs frozen in the laboratory to −2.5°C. Wood frogs in natural hibernacula remained frozen for 193±11 consecutive days and experienced average (October–May) temperatures of −6.3°C and average minimum temperatures of −14.6±2.8°C (range −8.9 to −18.1°C) with 100% survival (N=18). Mean glucose concentrations were 13-fold higher in muscle, 10-fold higher in heart and 3.3-fold higher in liver in naturally freezing compared with laboratory frozen frogs. Antifreeze glycolipid was present in extracts from muscle and internal organs, but not skin, of frozen frogs. Wood frogs in Interior Alaska survive freezing to extreme limits and durations compared with those described in animals collected in southern Canada or the Midwestern United States. We hypothesize that this enhancement of freeze tolerance in Alaskan wood frogs is due to higher cryoprotectant levels that are produced by repeated freezing and thawing cycles experienced under natural conditions during early autumn.

The Journal of Experimental Biology

9658876

10.1073/PNAS.0506590102

Short-amplitude high-frequency wing strokes determine the aerodynamics of honeybee flight.

Most insects are thought to fly by creating a leading-edge vortex that remains attached to the wing as it translates through a stroke. In the species examined so far, stroke amplitude is large, and most of the aerodynamic force is produced halfway through a stroke when translation velocities are highest. Here we demonstrate that honeybees use an alternative strategy, hovering with relatively low stroke amplitude (approximately 90 degrees) and high wingbeat frequency (approximately 230 Hz). When measured on a dynamically scaled robot, the kinematics of honeybee wings generate prominent force peaks during the beginning, middle, and end of each stroke, indicating the importance of additional unsteady mechanisms at stroke reversal. When challenged to fly in low-density heliox, bees responded by maintaining nearly constant wingbeat frequency while increasing stroke amplitude by nearly 50%. We examined the aerodynamic consequences of this change in wing motion by using artificial kinematic patterns in which amplitude was systematically increased in 5 degrees increments. To separate the aerodynamic effects of stroke velocity from those due to amplitude, we performed this analysis under both constant frequency and constant velocity conditions. The results indicate that unsteady forces during stroke reversal make a large contribution to net upward force during hovering but play a diminished role as the animal increases stroke amplitude and flight power. We suggest that the peculiar kinematics of bees may reflect either a specialization for increasing load capacity or a physiological limitation of their flight muscles.

Proceedings of the National Academy of Sciences of the United States of America

2901853

10.1242/JEB.035758

Deep supercooling, vitrification and limited survival to –100°C in the Alaskan beetle Cucujus clavipes puniceus (Coleoptera: Cucujidae) larvae

SUMMARY Larvae of the freeze-avoiding beetle Cucujus clavipes puniceus (Coleoptera: Cucujidae) in Alaska have mean supercooling points in winter of –35 to –42°C, with the lowest supercooling point recorded for an individual of –58°C. We previously noted that some larvae did not freeze when cooled to –80°C, and we speculated that these larvae vitrified. Here we present evidence through differential scanning calorimetry that C. c. puniceus larvae transition into a glass-like state at temperatures <–58°C and can avoid freezing to at least –150°C. This novel finding adds vitrification to the list of insect overwintering strategies. While overwintering beneath the bark of fallen trees, C. c. puniceus larvae may experience low ambient temperatures of around –40°C (and lower) when microhabitat is un-insulated because of low snow cover. Decreasing temperatures in winter are correlated with loss of body water from summer high levels near 2.0 to winter lows near 0.4 mg mg–1 dry mass and concomitant increases in glycerol concentrations (4–6 mol l–1) and thermal hysteresis. Finally, we provide direct evidence that Cucujus from Wiseman, Alaska, survive temperatures to –100°C.

The Journal of Experimental Biology

22375589

10.1007/S10886-005-5288-Z

Preformed and Induced Chemical Resistance of Tea Leaf Against Exobasidium vexans Infection

Levels of (−)-epicatechin in tea cultivars resistant to blister blight leaf disease were significantly higher than those in susceptible cultivars, while the reverse was true for (−)-epigallocatechin gallate, suggesting that epicatechin was involved in the resistance mechanism. The content of the methylxanthines, caffeine and theobromine, in the leaf increased in the initial translucent stage of the disease, probably as a defense response to fungal attack. Epicatechin and epigallocatechin levels were less than in healthy tissues at this stage, but increases in the corresponding gallate esters suggested that they were being converted into esters. Although epicatechin and epigallocatechin levels decreased from translucent to mature blister stages, the decrease was not significant. The decrease in levels of epicatechin, epigallocatechin, and their esters on infection and the formation of cyanidin and delphinidin on oxidative depolymerization of the blisters suggests that proanthocyanidins may play a role in the defense mechanism. The high resistance of a purple green leafed cultivar is attributed to the additional catechin source provided by the high levels of anthocyanins present.

Journal of Chemical Ecology

4459801

10.1038/NATURE20140

Variability in plant nutrients reduces insect herbivore performance

The performance and population dynamics of insect herbivores depend on the nutritive and defensive traits of their host plants. The literature on plant–herbivore interactions focuses on plant trait mean values, but recent studies showing the importance of plant genetic diversity for herbivores suggest that plant trait variance may be equally important. The consequences of plant trait variance for herbivore performance, however, have been largely overlooked. Here we report an extensive assessment of the effects of within-population plant trait variance on herbivore performance using 457 performance datasets from 53 species of insect herbivores. We show that variance in plant nutritive traits substantially reduces mean herbivore performance via non-linear averaging of performance relationships that were overwhelmingly concave down. By contrast, relationships between herbivore performance and plant defence levels were typically linear, with variance in plant defence not affecting herbivore performance via non-linear averaging. Our results demonstrate that plants contribute to the suppression of herbivore populations through variable nutrient levels, not just by having low average quality as is typically thought. We propose that this phenomenon could play a key role in the suppression of herbivore populations in natural systems, and that increased nutrient heterogeneity within agricultural crops could contribute to the sustainable control of insect pests in agroecosystems.

Nature

86131122

10.1111/J.1442-9993.2009.01973.X

Scale-dependent trait correlations in a temperate tree community

Recent investigations of relationships among plant traits have generated important insights into plant form and function. However, relationships involving leaf area, leaf shape and plant height remain poorly resolved. Previous work has also focused on correlations between average trait values for individual species. It is unclear whether similar relationships occur within species.We searched for novel plant trait correlations by comparing leaf area, leaf circularity, specific leaf area (SLA) and plant height among 16 common woody plant species from a temperate forest in New Zealand. Analyses were conducted both within species (intra-specifically) and among species (inter-specifically) to determine whether trait correlations were scale dependent. Leaf area was unrelated to other leaf traits inter-specifically. However, leaf area declined with plant height and increased with SLA intra- specifically. Leaf circularity decreased with plant height inter-specifically, but increased with plant height intra- specifically. SLA increased with plant height both inter- and intra-specifically. Leaf circularity increased with SLA inter-specifically, but decreased with SLA intra-specifically. Overall results showed that leaf shape, SLA and plant height are interrelated. However, intra-specific relationships often differed substantially from inter-specific rela- tionships, suggesting that the processes shaping relationships between this suite of plant traits are scale-dependent.

Austral Ecology

14750813

10.1073/PNAS.0906424106

Convergent evolution of metabolic roles in bacterial co-symbionts of insects

A strictly host-dependent lifestyle has profound evolutionary consequences for bacterial genomes. Most prominent is a sometimes-dramatic amount of gene loss and genome reduction. Recently, highly reduced genomes from the co-resident intracellular symbionts of sharpshooters were shown to exhibit a striking level of metabolic interdependence. One symbiont, called Sulcia muelleri (Bacteroidetes), can produce eight of the 10 essential amino acids, despite having a genome of only 245 kb. The other, Baumannia cicadellinicola (γ-Proteobacteria), can produce the remaining two essential amino acids as well as many vitamins. Cicadas also contain the symbiont Sulcia, but lack Baumannia and instead contain the co-resident symbiont Hodgkinia cicadicola (α-Proteobacteria). Here we report that, despite at least 200 million years of divergence, the two Sulcia genomes have nearly identical gene content and gene order. Additionally, we show that despite being phylogenetically distant and drastically different in genome size and architecture, Hodgkinia and Baumannia have converged on gene sets conferring similar capabilities for essential amino acid biosynthesis, in both cases precisely complementary to the pathways conserved in Sulcia. In contrast, they have completely divergent capabilities for vitamin biosynthesis. Despite having the smallest gene set known in bacteria, Hodgkinia devotes at least 7% of its proteome to cobalamin (vitamin B12) biosynthesis, a significant metabolic burden. The presence of these genes can be explained by Hodgkinia's retention of the cobalamin-dependent version of methionine synthase instead of the cobalamin-independent version found in Baumannia, a situation that necessitates retention of cobalamin biosynthetic capabilities to make the essential amino acid methionine.

Proceedings of the National Academy of Sciences of the United States of America

10307244

10.1242/JEB.038992

Stabilization and swelling of hagfish slime mucin vesicles

SUMMARY When agitated, Atlantic hagfish (Myxine glutinosa) produce large quantities of slime that consists of hydrated bundles of protein filaments and membrane-bound mucin vesicles from numerous slime glands. When the slime exudate contacts seawater, the thread bundles unravel and the mucin vesicles swell and rupture. Little is known about the mechanisms of vesicle rupture in seawater and stabilization within the gland, although it is believed that the vesicle membrane is permeable to most ions except polyvalent anions. We hypothesized that the most abundant compounds within the slime gland exudate have a stabilizing effect on the mucin vesicles. To test this hypothesis, we measured the chemical composition of the fluid component of hagfish slime exudate and conducted functional assays with these solutes to test their ability to keep the vesicles in a condensed state. We found K+ concentrations that were elevated relative to plasma, and Na+, Cl− and Ca2+ concentrations that were considerably lower. Our analysis also revealed high levels of methylamines such as trimethylamine oxide (TMAO), betaine and dimethylglycine, which had a combined concentration of 388 mmol l−1 in the glandular fluid. In vitro rupture assays demonstrated that both TMAO and betaine had a significant effect on rupture, but neither was capable of completely abolishing mucin swelling and rupture, even at high concentrations. This suggests that some other mechanism such as the chemical microenvironment within gland mucous cells, or hydrostatic pressure is responsible for stabilization of the vesicles within the gland.

The Journal of Experimental Biology

84818033

10.1016/J.FLORA.2005.06.010

Why some leaves are anthocyanic and why most anthocyanic leaves are red

Abstract The adaptive significance of leaf reddening, as it occurs during specific developmental stages or after stress, has puzzled biologists for more than a century. Theoretically, the accumulation of a non-photosynthetic pigment competing with chlorophylls for photon capture would impose a photosynthetic cost, which should be paid off by the benefits afforded by anthocyanins under some circumstances. Hence, the proposed hypotheses presume protective functions against excess light, UV-B radiation, reactive oxygen species, water stress (osmoregulation) and herbivory. The existing arguments in favor of an anti-oxidant, anti-UV-B and osmoregulatory role are confounded by the co-occurrence in leaves of other compounds having the same properties, not absorbing visible light, attaining much higher concentrations and, in some cases, having a more appropriate location to fulfill the ascribed functions. Moreover, the excess light hypothesis should take into account that anthocyanins mainly absorb green photons, which are used photosynthetically in deeper cell layers needing less photoprotection. The more ecological, anti-herbivore hypotheses, consider red leaf color as a signal denoting high defensive commitment, as a camouflage obscuring the green reflectance indicative of a healthy leaf and/or as a device undermining the folivorous insects camouflage. The anti-herbivore hypotheses have not been thoroughly tested, yet they are compatible with the known optical preferences of insects and their underlying physiology. Overall, although a multiplicity of potential roles can be argued, the primary role may depend on the reference system, i.e. species, developmental stage or specific biotic and abiotic stressors.

Flora

62833396

10.1111/J.1365-3040.2004.01223.X

Physiological and anatomical changes during the early ontogeny of the heteroblastic bromeliad, Vriesea sanguinolenta, do not concur with the morphological change from atmospheric to tank form

Two distinct morphological forms characterize the ontogeny of many epiphytic bromeliads. Smaller plants exhibit an atmospheric habit, while larger plants form water-impounding tanks. The study of the functional significance of heteroblasty in epiphytes is severely hampered by considerable size-related variation in morphological, anatomical and physiological parameters. To overcome this problem, plants of varying size of both atmospheric and tank form were included in the present study with Vriesea sanguinolenta. The results show that virtually all morphological, anatomical and physiological characteristics vary during ontogeny, but changes were rarely directly related to the step change in gross morphology. Changes were either: (1) gradual from smallest atmospheric to small tank (e.g. leaf divergence angles, reduction in photosystem II efficiency during drought, speed of recovery after drought); (2) there was no change between atmospheric and small tank, but a gradual or step change within the tank form (stomatal density, relationship of leaf N and specific leaf area); or (3) developmental patterns were more complicated with decreases and increases during ontogeny (photosynthetic capacity, carbon isotope ratios, abscisic acid levels during drought). Although the comparisons between ontogenetic phases were always confounded by size differences, a hypothetical small tank plant is expected to suffer higher water loss than a real atmospheric, whereas a hypothetical, large atmospheric plant would show reduced access to resources, such as nutrients, in comparison with the real tank. The present results are consistent with the notion of heteroblasty as an adaptation of early ontogenetic stages to drought, but highlight that size-related variation greatly modifies any difference directly associated with the step change from atmospheric to tank.

Plant Cell and Environment

34547654

10.1073/PNAS.1100296108

Evolution of restraint in a structured rock–paper–scissors community

It is not immediately clear how costly behavior that benefits others evolves by natural selection. By saving on inherent costs, individuals that do not contribute socially have a selective advantage over altruists if both types receive equal benefits. Restrained consumption of a common resource is a form of altruism. The cost of this kind of prudent behavior is that restrained individuals give up resources to less-restrained individuals. The benefit of restraint is that better resource management may prolong the persistence of the group. One way to dodge the problem of defection is for altruists to interact disproportionately with other altruists. With limited dispersal, restrained individuals persist because of interaction with like types, whereas it is the unrestrained individuals that must face the negative long-term consequences of their rapacity. Here, we study the evolution of restraint in a community of three competitors exhibiting a nontransitive (rock–paper–scissors) relationship. The nontransitivity ensures a form of negative feedback, whereby improvement in growth of one competitor has the counterintuitive consequence of lowering the density of that improved player. This negative feedback generates detrimental long-term consequences for unrestrained growth. Using both computer simulations and evolution experiments with a nontransitive community of Escherichia coli, we find that restrained growth can evolve under conditions of limited dispersal in which negative feedback is present. This research, thus, highlights a set of ecological conditions sufficient for the evolution of one form of altruism.

Proceedings of the National Academy of Sciences of the United States of America

7329395

10.1007/S12010-008-8286-0

Biodegradation of Fluoranthene by Basidiomycetes Fungal Isolate Pleurotus Ostreatus HP-1

The biodegradation of fluoranthene, a high molecular weight polycyclic aromatic hydrocarbon (PAH), was investigated in submerged culture using the wood decaying fungus isolated from forest locality in Gujarat, India. The basidiomycete fungal isolate was found to have an ability to grow on sabaroud dextrose agar containing 50 mgl−1 of each naphthalene, anthracene, acenaphthene, benzo (a) anthracene, pyrene, flouranthene, carbazole, and biphenyl. The involvement of extracellular fungal peroxidases such as manganese peroxidase (MnP) and laccase (Phenol oxidase) in the degradation of fluoranthene was studied. On the eighth day of incubation 54.09% of 70 mg l−1 fluoranthene was removed. There after no PAHs removal was observed till the 20th day of the incubation period. The isolate was identified as Pleurotus ostreatus by 18S rRNA, 5.8S rRNA, and partial 28S rRNA gene sequencing. To the best of our knowledge this is the first time Pleurotus ostreatus have been reported to degrade such a high concentration of fluoranthene within much lower time period of incubation. Depletion in the residual fluoranthene in the culture medium was determined by HPLC. Attempts were made to identify the degradation product in the culture medium with the help of FT-IR, NMR, and HPTLC analysis. In the present study positive correlation between fluoranthene degradation and the ligninolytic enzyme (MnP and laccase) production is observed, thus this isolate can play an effective role for bioremediation of PAHs contaminated sites.

Applied Biochemistry and Biotechnology

210802676

10.1016/J.MATT.2019.09.014

Arapaima Fish Scale: One of the Toughest Flexible Biological Materials

Summary For fish scales to provide protection from predators without severely compromising mobility, they must be lightweight, flexible, and tough. The arapaima fish scale is a superb example of this, enabling its survival in piranha-infested lakes of the Amazon. These elasmoid scales comprise two layers: a laminate composite of parallel collagen fibrils arranged in a Bouligand-like pattern and a highly mineralized surface layer that prevents initial penetration damage. Here, we measure its J-integral fracture toughness and find that the crack-growth toughness is ∼100–200 kJ⋅m−2, representing a very high fracture resistance for a natural material. This toughness results from multiple deformation mechanisms acting in concert in the twisted plywood structure of the scale, involving the collagenous lamellae at varying orientations retarding crack advance through stretching, reorientation, delamination and shear, and fracture. The toughness values obtained for the arapaima scales indicate that they are among the toughest of nature's flexible biological materials.

Matter

46060447

10.1128/JCM.37.9.3082-3082.1999

Intestinal Myiasis Caused by Eristalis tenax

Myiasis is the infestation of live humans and other vertebrate animals with dipterous larvae which, at least for a certain period, feed on the host’s dead or living tissue, liquid body substances, or ingested food ([3][1]). Clinically, myiasis may be classified as cutaneous, atrial, wound,

Journal of Clinical Microbiology

4289732

10.1038/194699A0

Uptake of Water by the Lizard, Moloch horridus

Moloch horridusis an agamid lizard living in the desert regions of Western and South Australia. It weighs as much as 50 gm. and has been described by Buxton1 as “a repulsive animal with tubercles and spines, it has the power of absorbing water through the skin after showers of rain”. This ability of absorbing water through the skin is characteristic of many Amphibia and is correlated with a ready loss of water by the same route2. Reptiles living in arid conditions would find a water-permeable skin uneconomical for water conservation so that this mode of taking up water may be questioned for Moloch.

Nature

5442547

10.1002/ANIE.201000825

Novel acetylenic oxylipins from the moss Dicranum scoparium with antifeeding activity against herbivorous slugs.

Mosses are seldom fed upon even in areas where intense herbivore pressure is observed on other plants. But even more than 100 years after the first investigations of Ernst Stahl on the chemical defense of plants and mosses against slugs and snails we know very little about the nature and biosynthesis of metabolites responsible for moss chemical defense. Dicranum scoparium is an example of a well-defended moss; it is globally distributed in temperate and arctic forests and often occurs in dense patches that show no sign of herbivory. In a recent survey of the volatile oxylipins (products of the oxidative transformation of polyunsaturated fatty acids) from mosses, we identified D. scoparium as a prolific producer of such metabolites. In addition, this moss produces unusual acetylenic cyclopentenones from the dominant acetylenic fatty acid dicranin presumably also by means of oxylipin pathways. Motivated by the observation that oxylipins often serve as defense metabolites or regulators of defense reactions in higher plants, 7] we explored the chemistry and chemical ecology of oxylipins of D. scoparium. As observed in higher plants and diatoms, the production of volatile oxylipins is triggered by mechanical wounding in mosses as well. Comparing the ultraperformance liquid chromatography/ mass spectrometry (UPLC/MS) profiles of methanolic extracts obtained from D. scoparium before and after tissue disruption revealed that a complex mixture of metabolites is produced within seconds after wounding (Figure 1). Owing to the complexity of the chromatograms, we aimed to address the metabolic pathways guided by biosynthetic precursors labeled with stable isotopes. Therefore we prepared monoand dideuterated fatty acids and administered them to the moss (Scheme 1). The acetylenic fatty acid dicranin proved to be of special interest as a precursor of unusual novel oxylipins. After a 10 min administration of monoor dideuterated dicranin suspended in water to frozen powdered moss, a complex mix of deuterated metabolites formed. Since not all oxylipins were chromatographically separated a manual evaluation of UPLC/MS data ran the risk of overlooking relevant signals. We therefore used an automated peak extraction routine that delivers mass/retention time pairs for every compound. These data from nontreated controls and mixtures obtained after treatment with monoor dideuterated dicranin were then evaluated using a canonical analysis of principal coordinates that enabled the rapid identification of dicranin-derived peaks (Figure 1; see the Supporting Information for experimental details). In contrast to the established manual evaluation of UPLC/MS runs this analysis allows an automated quick and comprehensive survey of metabolites derived from labeled precursors. This method covers the entire range of polarities and molecular weights recorded in LC/MS runs and picks up even minor or chromatographically not separated metabolites. The use of two precursors with different degrees of labeling in separate experiments supports the automated evaluation of the chromatogram since the second treatment serves as additional independent replicate (Figure 1c). The use of only one labeled precursor is also feasible, but more care has to be taken in the manual verification of the identified signals to avoid false positive hits. Mass/retention time pairs identified in the canonical analysis were used as guides in the purification of dicranin-derived metabolites using preparative HPLC. Structure elucidation of compounds 2–6 and 8 was based on oneand two-dimensional NMR as well as UV, IR, and MS data. The structure of 7 was tentatively assigned based on derivatization and GC/MS data. Scheme 1. Synthesis of monoand dideuterated fatty aicds. a) LDA, quenching with MeOD; b) NaOMe/MeOD; c) KOH/H2O.

Angewandte Chemie

3018932

10.1038/423021A

Structural biology: Life's transistors

Voltage-gated ion channels control electrical activity in nerve, muscle and many other cell types. The crystal structure of a bacterial voltage-gated channel reveals the astonishingly simple design of its voltage sensor.

Nature

15776818

10.1242/JEB.002071

Aerodynamic force generation, performance and control of body orientation during gliding in sugar gliders (Petaurus breviceps)

SUMMARY Gliding has often been discussed in the literature as a possible precursor to powered flight in vertebrates, but few studies exist on the mechanics of gliding in living animals. In this study I analyzed the 3D kinematics of sugar gliders (Petaurus breviceps) during short glides in an enclosed space. Short segments of the glide were captured on video, and the positions of marked anatomical landmarks were used to compute linear distances and angles, as well as whole body velocities and accelerations. From the whole body accelerations I estimated the aerodynamic forces generated by the animals. I computed the correlations between movements of the limbs and body rotations to examine the control of orientation during flight. Finally, I compared these results to those of my earlier study on the similarly sized and distantly related southern flying squirrel (Glaucomys volans). The sugar gliders in this study accelerated downward slightly (1.0±0.5 m s–2), and also accelerated forward (2.1±0.6 m s–2) in all but one trial, indicating that the body weight was not fully supported by aerodynamic forces and that some of the lift produced forward acceleration rather than just balancing body weight. The gliders used high angles of attack (44.15±3.12°), far higher than the angles at which airplane wings would stall, yet generated higher lift coefficients (1.48±0.18) than would be expected for a stalled wing. Movements of the limbs were strongly correlated with body rotations, suggesting that sugar gliders make extensive use of limb movements to control their orientation during gliding flight. In addition, among individuals, different limb movements were associated with a given body rotation, suggesting that individual variation exists in the control of body rotations. Under similar conditions, flying squirrels generated higher lift coefficients and lower drag coefficients than sugar gliders, yet had only marginally shallower glides. Flying squirrels have a number of morphological specializations not shared by sugar gliders that may help to explain their greater lift generating performance.

The Journal of Experimental Biology

35829996

10.1103/PHYSREVLETT.104.158302

Light-harvesting mechanism of bacteria exploits a critical interplay between the dynamics of transport and trapping.

Light-harvesting bacteria Rhodospirillum photometricum were recently found to adopt strikingly different architectures depending on illumination conditions. We present analytic and numerical calculations which explain this observation by quantifying a dynamical interplay between excitation transfer kinetics and reaction center cycling. High light-intensity membranes exploit dissipation as a photoprotective mechanism, thereby safeguarding a steady supply of chemical energy, while low light-intensity membranes efficiently process unused illumination intensity by channeling it to open reaction centers. More generally, our analysis elucidates and quantifies the trade-offs in natural network design for solar energy conversion.

Physical Review Letters

23694770

10.1088/1748-3182/3/4/046005

Bristled shark skin: a microgeometry for boundary layer control?

There exists evidence that some fast-swimming shark species may have the ability to bristle their scales during fast swimming. Experimental work using a water tunnel facility has been performed to investigate the flow field over and within a bristled shark skin model submerged within a boundary layer to deduce the possible boundary layer control mechanisms being used by these fast-swimming sharks. Fluorescent dye flow visualization provides evidence of the formation of embedded cavity vortices within the scales. Digital particle image velocimetry (DPIV) data, used to evaluate the cavity vortex formation and boundary layer characteristics close to the surface, indicate increased momentum in the slip layer forming above the scales. This increase in flow velocity close to the shark's skin is indicative of boundary layer control mechanisms leading to separation control and possibly transition delay for the bristled shark skin microgeometry.

Bioinspiration & Biomimetics

73661927

10.1111/J.1365-2907.2005.00067.X

Ecological impact of beavers Castor fiber and Castor canadensis and their ability to modify ecosystems

The genus Castor comprises two species: the Eurasian beaver Castor fibre , and the North American beaver Castor canadensis . Both species suffered from overexploitation, but have seen a revival since the 1920s due to increased protection and reintroduction programmes. Increases in the populations and distributions of species that are able to modify ecosystems have generated much scientific interest. Here we review the available literature concerning the possible ecological impact of beaver species in the Old and New World. 2. Beavers, being ecosystem engineers, are among the few species besides humans that can significantly change the geomorphology, and consequently the hydrological characteristics and biotic properties of the landscape. In so doing, beavers increase heterogeneity, and habitat and species diversity at the landscape scale. Beaver foraging also has a considerable impact on the course of ecological succession, species composition and structure of plant commu- nities, making them a good example of ecologically dominant species (e.g. keystone species). 3. Nevertheless, the strength of beavers' impact varies from site to site, depending on the geographical location, relief and the impounded habitat type. Consequently, they may not be significant controlling agents of the ecosystem in all parts of their distribution, but have strong interactions only under certain circumstances. We suggest that beavers can create important management opportunities in the Holarctic, and this review will help land man- agers determine the likely outcome of beaver activity.

Mammal Review

39992

10.1093/JXB/ERP359

Induced production of antifungal naphthoquinones in the pitchers of the carnivorous plant Nepenthes khasiana

Nepenthes spp. are carnivorous plants that have developed insect capturing traps, evolved by specific modification of the leaf tips, and are able to utilize insect degradation products as nutritional precursors. A chitin-induced antifungal ability, based on the production and secretion to the trap liquid of droserone and 5-O-methyldroserone, is described here. Such specific secretion uniquely occurred when chitin injection was used as the eliciting agent and probably reflects a certain kind of defence mechanism that has been evolved for protecting the carnivory-based provision of nutritional precursors. The pitcher liquid containing droserone and 5-O-methyldroserone at 3:1 or 4:1 molar ratio, as well as the purified naphthoquinones, exerted an antifungal effect on a wide range of plant and human fungal pathogens. When tested against Candida and Aspergillus spp., the concentrations required for achieving inhibitory and fungicidal effects were significantly lower than those causing cytotoxicity in cells of the human embryonic kidney cell line, 293T. These naturally secreted 1,4-naphthoquinone derivatives, that are assumed to act via semiquinone enhancement of free radical production, may offer a new lead to develop alternative antifungal drugs with reduced selectable pressure for potentially evolved resistance.

Journal of Experimental Botany

43178325

10.1016/S0300-9629(96)00270-8

Organic solutes in freezing tolerance.

The accumulation of high levels of low-molecular-weight solutes (polyhydric alcohols, saccharides) provides cryoprotection to freeze-tolerant animals by minimizing, via colligative effects, the percentage of body water converted to extracellular ice and the extent of cell volume reduction. Many freeze-tolerant insects accumulate high levels of polyols during autumn cold hardening, whereas freeze-tolerant frogs respond to ice formation in peripheral tissues by synthesizing large amounts of glucose in the liver and rapidly distributing the sugar throughout the body. Seasonal patterns of enzymatic change occur in cold-hardy insects; activities associated with cryoprotectant synthesis rise in the fall, whereas enzymes associated with polyol degradation dominate in the spring. Enzyme profiles also revealed the route of glycerol degradation via polyol dehydrogenase and the novel enzyme, glyceraldehyde kinase. Proton magnetic resonance imaging of freezing and thawing in whole frogs showed a new adaptive effect of the very high glucose levels in core organs; during thawing, organs such as liver and heart melted first, allowing recovery of their vital functions to begin while the rest of the frog thawed. New studies have examined signal transduction in the stimulation of glucose production by wood frog liver, revealing the key role of beta-adrenergic receptors and cAMP-mediated activation of glycogenolysis for cryoprotectant synthesis. The seasonal elevation of plasma membrane glucose transporters was also shown to be key to cryoprotectant distribution during freezing. Other new work has shown that frog freeze tolerance probably grew out of preexisting mechanisms of amphibian dehydration tolerance and that both freeze-tolerant and -intolerant frogs show a hyperglycemic response to desiccation at 5 degrees C.

Comparative Biochemistry and Physiology Part A: Physiology

108746887

10.1109/IEMT.2003.1225901

Current challenges in traditional design verification and its application in flip-chip devices

The acceleration of new developments in semiconductor design and manufacturing technology in keeping up with Moore's Law has introduced significant new challenges for device designers as well as manufacturing organizations. Short channel effects, multi-level interconnect cross talk problems, and new materials such as low K dielectric, copper, and silicon on insulator have made modeling and simulation of semiconductor devices and processes extremely difficult. Many times this results in failure to meet performance targets in first silicon introduction. The high cost of mask sets, together with the opportunity costs related to time-to-market, drives the need for shorter and fewer redesign cycles, making effective transistor level design debug a necessity. To make things even more difficult, the transition to flip chip packaging and multiple interconnect metal layers makes backside probing the only effective way to perform node level analysis. This paper describes these new challenges in detail, and the use of photon probing technology as an effective way to address them. The use of a time resolved photon emission microscope allows measuring performance at the critical node level. This is done by collecting the photons, emitted by carriers that are accelerated in the pinch off region during CMOS transistor switching. This enables optimization of device speed paths, and resolution of problems such as race conditions and contentions, encountered during design debug and failure analysis cycles.

International Electronics Manufacturing Technology Symposium

26768333

10.1890/08-1858.1

Chemical niche differentiation among sympatric species of orchid bees.

Male Neotropical orchid bees (Euglossini) collect volatile substances (fragrances) from flowers and other sources (e.g., decaying wood) and store them in specialized hind tibial pockets. The accumulated chemicals are later emitted during courtship display, presumably to lure conspecific females for mating. We analyzed tibial fragrances of males of 15 sympatric Panamanian species in the genus Euglossa to test whether communities of euglossine bees are chemically structured, and to elucidate whether male fragrance signals evolve to convey premating isolation. Our analysis revealed substantial chemical disparity among all lineages. Disparity was mediated by compounds that were exclusive to certain species but also by differences in relative quantity of shared compounds. We mapped tibial fragrance compounds present in each species on a DNA-based phylogeny (reconstructed using partial sequences of COI, EF1-alpha, ArgK, and Pol-II) and found that most dominant compounds were highly homoplasious. In an analysis of chemical differentiation in relation to phylogenetic divergence through time, disparity was greater than expected from a null model at any point during evolutionary history, suggesting that diversifying selection has shaped fragrance phenotypes. Notably, chemical disparity was greater within recently diverged lineages than among them, suggesting that chemical preferences in orchid bees evolved rapidly in the early stages of species divergence. We postulate communication interference as the possible mechanism behind the observed fragrance differentiation, which may be the product of reproductive character (fragrance) displacement. Our findings are consistent with the hypothesis that male fragrance signals evolve to convey premating isolation.

Ecology

53163867

10.1016/J.ANBEHAV.2010.01.011

Do desert ants smell the scenery in stereo?

Desert ants, Cataglyphis fortis, navigate individually in the inhospitable saltpans of Tunisia using path integration for long-distance navigation, and visual and olfactory landmarks for fine-scale orientation in the vicinity of the nest entrance. Here, we show in a field experiment that the ants are able to locate the nest entrance within a two-dimensional olfactory array. Ants were trained to forage in an open channel and to memorize the nest entrance relative to four odours that were applied at the corners of an invisible quadratic array. In a test situation, the ants pinpointed the fictive nest only when the odours were present at their learned positions. Our results suggest that the ants had learned the olfactory scenery around their nest. Furthermore, unilaterally antennectomized ants could not pinpoint the nest within a two-dimensional array. Hence, this kind of orientation depends on the simultaneous input of both antennae, that is, on a stereo sense of smell. Until now, insects and mammals, including humans, have only been known to use bilateral sensory input to follow a concentration gradient of an odour. Our evidence suggests that desert ants require a stereo sense of smell to make use of the olfactory scenery around their nest for homing.

Animal Behaviour

23364137

10.1126/SCIENCE.1255718

Sidewinding with minimal slip: Snake and robot ascent of sandy slopes

Limbless organisms such as snakes can navigate nearly all terrain. In particular, desert-dwelling sidewinder rattlesnakes (Crotalus cerastes) operate effectively on inclined granular media (such as sand dunes) that induce failure in field-tested limbless robots through slipping and pitching. Our laboratory experiments reveal that as granular incline angle increases, sidewinder rattlesnakes increase the length of their body in contact with the sand. Implementing this strategy in a physical robot model of the snake enables the device to ascend sandy slopes close to the angle of maximum slope stability. Plate drag experiments demonstrate that granular yield stresses decrease with increasing incline angle. Together, these three approaches demonstrate how sidewinding with contact-length control mitigates failure on granular media. Robots based on sidewinder rattlesnakes are used to understand motion on sloped granular terrain. [Also see Perspective by Socha] What's that coming over the hill—is it a robot? Crossing a slope can be difficult, particularly if it is made of sand. Sidewinder rattlesnakes manage to climb sandy hills by adjusting the length of their body in contact with the sand. Marvi et al. designed robots based on this idea to determine what affects climbing ability on sandy slopes (see the Perspective by Socha). Based on the behavior of the robots, the authors performed further animal studies, and used an iterative approach to improve the robots' capabilities and to better understand animal motion. Science, this issue p. 224; see also p. 160

Science

21509123

10.1146/ANNUREV.BIOCHEM.68.1.425

Cellular and molecular biology of the aquaporin water channels.

The high water permeability characteristic of mammalian red cell membranes is now known to be caused by the protein AQP1. This channel freely permits movement of water across the cell membrane, but it is not permeated by other small, uncharged molecules or charged solutes. AQP1 is a tetramer with each subunit containing an aqueous pore likened to an hourglass formed by obversely arranged tandem repeats. Cryoelectron microscopy of reconstituted AQP1 membrane crystals has revealed the three-dimensional structure at 3-6 A. AQP1 is distributed in apical and basolateral membranes of renal proximal tubules and descending thin limbs as well as capillary endothelia. Ten mammalian aquaporins have been identified in water-permeable tissues and fall into two groupings. Orthodox aquaporins are water-selective and include AQP2, a vasopressin-regulated water channel in renal collecting duct, in addition to AQP0, AQP4, and AQP5. Multifunctional aquaglyceroporins AQP3, AQP7, and AQP9 are permeated by water, glycerol, and some other solutes. Aquaporins are being defined in numerous other species including amphibia, insects, plants, and microbials. Members of the aquaporin family are implicated in numerous physiological processes as well as the pathophysiology of a wide range of clinical disorders.

Annual Review of Biochemistry

31295826

10.1073/PNAS.0908712106

The physical state of water in bacterial spores

The bacterial spore, the hardiest known life form, can survive in a metabolically dormant state for many years and can withstand high temperatures, radiation, and toxic chemicals. The molecular basis of spore dormancy and resistance is not understood, but the physical state of water in the different spore compartments is thought to play a key role. To characterize this water in situ, we recorded the water 2H and 17O spin relaxation rates in D2O-exchanged Bacillus subtilis spores over a wide frequency range. The data indicate high water mobility throughout the spore, comparable with binary protein–water systems at similar hydration levels. Even in the dense core, the average water rotational correlation time is only 50 ps. Spore dormancy therefore cannot be explained by glass-like quenching of molecular diffusion but may be linked to dehydration-induced conformational changes in key enzymes. The data demonstrate that most spore proteins are rotationally immobilized, which may contribute to heat resistance by preventing heat-denatured proteins from aggregating irreversibly. We also find that the water permeability of the inner membrane is at least 2 orders of magnitude lower than for model membranes, consistent with the reported high degree of lipid immobilization in this membrane and with its proposed role in spore resistance to chemicals that damage DNA. The quantitative results reported here on water mobility and transport provide important clues about the mechanism of spore dormancy and resistance, with relevance to food preservation, disease prevention, and astrobiology.

Proceedings of the National Academy of Sciences of the United States of America

335812

10.1242/JEB.041962

Comparative jet wake structure and swimming performance of salps

SUMMARY Salps are barrel-shaped marine invertebrates that swim by jet propulsion. Morphological variations among species and life-cycle stages are accompanied by differences in swimming mode. The goal of this investigation was to compare propulsive jet wakes and swimming performance variables among morphologically distinct salp species (Pegea confoederata, Weelia (Salpa) cylindrica, Cyclosalpa sp.) and relate swimming patterns to ecological function. Using a combination of in situ dye visualization and particle image velocimetry (PIV) measurements, we describe properties of the jet wake and swimming performance variables including thrust, drag and propulsive efficiency. Locomotion by all species investigated was achieved via vortex ring propulsion. The slow-swimming P. confoederata produced the highest weight-specific thrust (T=53 N kg–1) and swam with the highest whole-cycle propulsive efficiency (ηwc=55%). The fast-swimming W. cylindrica had the most streamlined body shape but produced an intermediate weight-specific thrust (T=30 N kg–1) and swam with an intermediate whole-cycle propulsive efficiency (ηwc=52%). Weak swimming performance variables in the slow-swimming C. affinis, including the lowest weight-specific thrust (T=25 N kg–1) and lowest whole-cycle propulsive efficiency (ηwc=47%), may be compensated by low energetic requirements. Swimming performance variables are considered in the context of ecological roles and evolutionary relationships.

The Journal of Experimental Biology

8294653

10.1098/RSPB.2010.2084

From the first intention movement to the last joiner: macaques combine mimetic rules to optimize their collective decisions

Mechanisms related to collective decision making have recently been found in almost all animal reigns from amoebae to worms, insects and vertebrates, including human beings. Decision-making mechanisms related to collective movements—including pre-departure and joining—have already been studied at different steps of the movement process, but these studies were always carried out separately. We therefore have no understanding of how these different processes are related when they underlie the same collective decision-making event. Here, we consider the whole departure process of two groups of Tonkean macaques (Macaca tonkeana), using a stochastic model. When several exclusive choices are proposed, macaques vote and choose the majority. Individuals then join the movement according to a mimetism based on affiliative relationships. The pre-departure quorum and the joining mimetic mechanism are probably linked, but we have not yet identified which transition mechanism is used. This study shows that decision-making related to macaque group movements is governed by a quorum rule combined with a selective mimetism at departure. This is the first time that transition mechanisms have been described in mammals, which consequently helps understand how a voting process leads to social amplification. Our study also provides the first complete proof that there is continuity in the decision-making processes underlying collective movements in mammals from the first intention movement right through to the last joiner.

Proceedings of The Royal Society B: Biological Sciences

23263965

10.2307/2656682

Reorientation of daffodil(Narcissus: Amaryllidaceae) flowers inwind: drag reduction andtorsional flexibility.

Daffodil flowers extend laterally from the long axes of their stems; as a result, wind on a flower exerts torsional as well as flexural stress on the stem. Stems respond by twisting, and thus flowers reorient to face downwind in moderate winds, in the process reducing their drag by ∼30%. This repositioning is facilitated by the stems' relatively low torsional stiffness. Daffodil stems have a ratio of flexural to torsional stiffness of 13.27 ± 0.96 (SD), compared with 8.33 ± 3.20 (SD) for tulip stems, which bear flowers as symmetrical extensions of their long axes, and compared with 1.5 for isotropic, incompressible, circular cylinders.

American Journal of Botany

20524790

10.1007/BF02381090

Aspilia spp. Leaves: A puzzle in the feeding behavior of wild chimpanzees

Unlike other chimpanzee food items, the leaves ofAspilia pluriseta, A. rudis and A. mossambicensis (Compositae) are eaten without being chewed. Moreover,A. pluriseta andA. rudis are eaten slowly and singly and particularly in the early morning. This unusual behavior suggests thatAspilia leaves offer peculiar stimuli, perhaps with pharmacological effects.

Primates

11480397

10.1111/J.1365-2915.2009.00809.X

Efficacy and safety of catnip (Nepeta cataria) as a novel filth fly repellent *

Catnip (Nepeta cataria) is known for its pseudo‐narcotic effects on cats. Recently, it has been reported as an effective mosquito repellent against several Aedes and Culex species, both topically and spatially. Our laboratory bioassays showed that catnip essential oil (at a dosage of 20 mg) resulted in average repellency rates of 96% against stable flies, Stomoxys calcitrans (L.) and 79% against houseflies, Musca domestica (L.), respectively. This finding suggested that the application of repellent could be used as part of filth fly management. Further evaluations of catnip oil toxicity were conducted to provide a broad‐spectrum safety profile of catnip oil use as a potential biting and nuisance insect repellent in urban settings. Acute oral, dermal, inhalation, primary dermal and eye irritation toxicity tests were performed. The acute oral LD50 of catnip oil was found to be 3160 mg/kg body weight (BW) and 2710 mg/kg BW in female and male rats, respectively. The acute dermal LD50 was > 5000 mg/kg BW. The acute inhalation LD50 was observed to be > 10 000 mg/m3. Primary skin irritation tested on New Zealand white rabbits showed that catnip oil is a moderate irritant. Catnip oil was classified as practically non‐irritating to the eye. In comparison with other U.S. Environmental Protection Agency‐approved mosquito repellents (DEET, picaridin and p‐menthane‐3,8‐diol), catnip oil can be considered as a relatively safe repellent, which may cause minor skin irritation.

Medical and Veterinary Entomology

135681723

10.1557/JMR.2005.0171

Platelet interlocks are the key to toughness and strength in nacre

Nacre, the inner layer of mollusk shells is a composite made of platelets of mineral aragonitic calcium carbonate with a few weight percent organic material sandwiched in between. The organic and nanostructural nuances are often suggested to be the reason for the extreme toughness of nacre. Here we report the presence of interlocks between platelets of nacre from red abalone. We also report and show, using three-dimensional finite element modeling, that interlocks are the key mechanism for the high toughness and strength of nacre. The observed rotation between platelet layers, which were earlier reported as defects of structure, are necessary for the formation of interlocks.

Journal of Materials Research

4336989

10.1038/NATURE01416

Architecture and material properties of diatom shells provide effective mechanical protection

Diatoms are the major contributors to phytoplankton blooms in lakes and in the sea and hence are central in aquatic ecosystems and the global carbon cycle. All free-living diatoms differ from other phytoplankton groups in having silicified cell walls in the form of two ‘shells’ (the frustule) of manifold shape and intricate architecture whose function and role, if any, in contributing to the evolutionary success of diatoms is under debate. We explored the defence potential of the frustules as armour against predators by measuring their strength. Real and virtual loading tests (using calibrated glass microneedles and finite element analysis) were performed on centric and pennate diatom cells. Here we show that the frustules are remarkably strong by virtue of their architecture and the material properties of the diatom silica. We conclude that diatom frustules have evolved as mechanical protection for the cells because exceptional force is required to break them. The evolutionary arms race between diatoms and their specialized predators will have had considerable influence in structuring pelagic food webs and biogeochemical cycles.

Nature

43498299

10.1016/J.PLANTSCI.2011.04.016

An overview on plant cuticle biomechanics.

Plant biomechanics combines the principles of physics, chemistry and engineering to answer questions about plant growth, development and interaction with the environment. The epidermal-growth-control theory, postulated in 1867 and verified in 2007, states that epidermal cells determine the rate of organ elongation since they are under tension, while inner tissues are under compression. The lipid cuticle layer is deposited on the surface of outer epidermal cell walls and modifies the chemical and mechanical nature of these cell walls. Thus, the plant cuticle plays a key role in plant interaction with the environment and in controlling organ expansion. Rheological analyses indicate that the cuticle is a mostly viscoelastic and strain-hardening material that stiffens the comparatively more elastic epidermal cell walls. Cuticle stiffness can be attributed to polysaccharides and flavonoids present in the cuticle whereas a cutin matrix is mainly responsible for its extensibility. Environmental conditions such as temperature and relative humidity have a plasticizing effect on the mechanical properties of cuticle since they lower cuticle stiffness and strength. The external appearance of agricultural commodities, especially fruits, is of great economic value. Mechanical properties of the cuticle can have a positive or negative effect on disorders like fruit cracking, fungal pathogen penetration and pest infestation. Cuticle rheology has significant variability within a species and thus can be subjected to selection in order to breed cultivars resistant to pests, infestation and disorders.

Plant Science

21991310

10.1093/JMICRO/DFL002

The thermogenic center in social wasps.

In the social wasps Vespa orientalis and Paravespula germanica (Hymenoptera, Vespinae), a thermogenic center has been found in the dorsal part of the first thoracic segment. The temperature in this region of the prothorax is higher by 6-9 degrees C than that at the tip of the abdomen, and this in actively flying hornets outside the nest (workers, males or queens) as well as in hornets inside the nest that attend to the brood in the combs. On viewing the region from the outside, one discerns a canal or rather a fissure in the cuticle, which commences at the center of the dorsal surface of the prothorax and extends till the mesothorax. Thus the length of this canal or fissure is approximately 5-7 mm and it is seen to contain numerous thin hairs whose shape varies from that of the hairs alongside the structure. Beneath the cuticle in this region there are dorsoventral as well as longitudinal muscles in abundance, much the same as the musculature in the remaining thoracic segments (i.e. the meso- and metathorax), which activate the two pairs of wings. The canal-bearing segment is of course devoid of wings, and its dorsoventral muscles are attached to the cuticle, which in this region resembles a bowl harboring several layers of epithelium that boasts numerous butterfly-shaped tracheal branches. Additionally there are layers that display lymph-filled spaces and also perforated layers and depressions, and beneath all these is a lace-like layer that also coats the cuticle's hollows. Underneath the cuticle proper, there are numerous large mitochondria and tracheae, which occupy a considerable part of the cuticular epithelium surface. These abundant mitochondria are, most probably, the main element of heat production in the thermogenic center.

Journal of Electron Microscopy

22388568

10.1080/0892701031000061769

Surface Properties of the Skin of the Pilot Whale Globicephala melas

On the skin surface of delphinids small biofoulers are challenged to high shear water flow and liquid-vapor interfaces of air-bubbles during jumping. This state of self-cleaning is supported by the even, nano-rough gel-coated epidermal surface of the skin. The present study focussed on the intercellular evolution of gel formation and the chemical composition of the gel smoothing the skin surface of the pilot whale, Globicephala melas , using X-ray photoelectron spectroscopy (XPS) in combination with cryo-scanning electron microscopy (CSM), and transmission electron microscopy (TEM). In the superficial layer of the epidermis, the stratum corneum, intercellular material was shown by electron optical methods to assemble from smaller into larger covalently cross-linked aggregates during the transit of the corneocytes towards the skin surface. XPS measurements showed that the surface of the skin and the intercellular gel included approximately the same amounts of polar groups (especially, free amines and amides) and non-polar groups, corresponding to the presence of lipid droplets dispersed within the jelly material. It was concluded from the results that the gel-coat of the skin surface is a chemically heterogeneous skin product. The advantages of chemically heterogeneous patches contributing to the ablation of traces of the biofouling process are discussed.

Biofouling

4415713

10.1038/37745

How pine cones open

The scales of seed-bearing pine cones move in response to changes in relative humidity. The scales gape open when it is dry, releasing the cone's seeds. When it is damp, the scales close up. The cells in a mature cone are dead, so the mechanism is passive: the structure of the scale and the walls of the cells composing the scale respond to changing relative humidity. Dissection of cones from the Monterey pine, Pinus radiata, revealed to us two types of scale growing from the main body of the cone — the ovuliferous scale and the bract scale. The larger ovuliferous scales respond to changes in relative humidity when removed from the body of the cone.

Nature

11326447

10.1210/EN.2003-0418

Regulation of water absorption in the frog skins by two vasotocin-dependent water-channel aquaporins, AQP-h2 and AQP-h3.

A new frog aquaporin (AQP) cDNA was cloned from a cDNA library constructed from the ventral skin of the tree frog Hyla japonica. This AQP (Hyla AQP-h2) consisted of 268 amino acid residues with a high homology to mammalian AQP2. The predicted amino acid sequence contained the two conserved Asn-Pro-Ala motifs found in all the major intrinsic protein family members and the putative six transmembrane domains. The sequence also contained a mercurial compound: cysteine, one potential N-glycosylation site at Asn-124, and a putative phosphorylation site recognized by protein kinase A at Ser-262. In a swelling assay using Xenopus oocytes, AQP-h2 facilitated water permeability, especially in response to cAMP. Expression of AQP-h2 mRNA was restricted to several tissues including the ventral skin, kidney, and urinary bladder; but with immunofluorescence staining using an antipeptide antibody (ST-140) against the AQP-h2 protein, immunopositive cells were found only in the ventral skin and urinary bladder. In the ventral pelvic skin, the label for AQP-h2 was localized in the entire plasma membrane of the granular cells beneath the outmost layer of the skin and in the basolateral membrane of the granular cells in this layer. In response to vasotocin, however, the label for AQP-h2 became more intense in the apical membrane in the granular cells of the outermost layer, similar to the case for the earlier studied AQP-h3, which was specifically expressed in the ventral skin. Taken together, these findings suggest that not only AQP-h3, but also AQP-h2 acts as a regulator of the water balance in this frog.

Endocrinology

23817342

10.1098/RSBL.2006.0455

Direct uptake of soil nitrogen by mosses

Mosses are one of the most diverse and widespread groups of plants and often form the dominant vegetation in montane, boreal and arctic ecosystems. However, unlike higher plants, mosses lack developed root and vascular systems, which is thought to limit their access to soil nutrients. Here, we test the ability of two physiologically and taxonomically distinct moss species to take up soil- and wet deposition-derived nitrogen (N) in natural intact turfs using stable isotopic techniques (15N). Both species exhibited increased concentrations of shoot 15N when exposed to either soil- or wet deposition-derived 15N, demonstrating conclusively and for the first time, that mosses derive N from the soil. Given the broad physiological and taxonomic differences between these moss species, we suggest soil N uptake may be common among mosses, although further studies are required to test this prediction. Soil N uptake by moss species may allow them to compete for soil N in a wide range of ecosystems. Moreover, since many terrestrial ecosystems are N limited, soil N uptake by mosses may have implications for plant community structure and nutrient cycling. Finally, soil N uptake may place some moss species at greater risk from N pollution than previously appreciated.

Biology Letters

26100514

10.3732/AJB.1000286

Root contraction helps protect the "living rock" cactus Ariocarpus fissuratus from lethal high temperatures when growing in rocky soil.

UNLABELLED PREMISE OF THE STUDY We investigated how the "living rock" cactus Ariocarpus fissuratus, like other low-growing desert plants, can endure potentially lethal high temperatures at the soil surface. Specifically, we examined how shoot descent by root contraction in the presence or absence of soil rocks influences shoot temperatures and transpiration. • METHODS Root contraction was identified by measuring shoot descent and anatomical analysis. Temperatures and transpiration were measured for plants at two heights in sandy and rocky soil, and temperature tolerances were determined by vital staining. • KEY RESULTS Plants embedded in rocky soil survived an extreme heat episode, unlike plants in sandy soil, though rocks did not moderate low temperatures. Root contraction occurred regardless of season and soil moisture. Xylem conduits (wide-band tracheids) formed a compressible lattice that decreased root length as rays enlarged the root base radially. Plant position in the soil did not affect transpiration. • CONCLUSIONS Contractile roots pulled plants of A. fissuratus into the soil at rates of 6-30 mm yr(-1). Maintaining shoots level with the soil surface kept plant temperatures below the high lethal temperature and improved survivorship in soil shaded by surface rocks.

American Journal of Botany

87960201

10.2307/1443948

Skin Structure and Wiping Behavior of Phyllomedusine Frogs

Four species of the genus Phyllomedusa (sauvagei, iherengi, pailona and hypochondrialis) were found to have previously undescribed integumental alveolar glands which contain lipid material. No lipid glands were observed in Agalychnis annae and very few in Pachymedusa dacnicolor, two other members of the subfamily Phyllomedusinae. The four species of Phyllomedusa demonstrate a complex and stereotyped wiping of the body surface immediately after the secretion of lipid. These frogs demonstrate very low evaporative water loss through the skin. The low water loss is associated with a constellation of behavioral and physiological characters: the selection of a permanent perch where the frogs remain during the day, the secretion of lipid by skin glands, wiping behavior and the assumption of torpor. Light and electron microscopy of the integument of these frogs demonstrated a typical anuran skin, with the exception of the presence of lipid glands. The impermeability of the skin is attributed to the formation of a lipid layer on the skin surface.

Copeia

10276965

10.1105/TPC.109.066605

DAY NEUTRAL FLOWERING Represses CONSTANS to Prevent Arabidopsis Flowering Early in Short Days[W][OA]

This work describes the flowering time gene DAY NEUTRAL FLOWERING (DNF), which acts in the same flowering pathway as CONSTANS (CO). DNF is a membrane-bound E3 ligase that represses CO expression and plays an important role in maintaining low levels of CO expression in short days; it is thus essential for the ability of the Arabidopsis plant to have a different flowering response in long and short days. The photoperiodic response in Arabidopsis thaliana requires the precise regulation of CONSTANS (CO) expression in relation to the light period during the day. In short days (SDs) levels of CO expression are normally low during the light period, and this results in delayed flowering compared with long days (LDs) when CO expression rises to high levels before the end of the light period. We identified a novel flowering time gene called DAY NEUTRAL FLOWERING (DNF) that acts in the same flowering pathway as CO. DNF is a membrane-bound E3 ligase that represses CO expression and plays an important role in maintaining low levels of CO expression in SDs. The effect of DNF on the rhythm of CO expression is essential for the photoperiodic response of Arabidopsis, enabling it to have a different flowering response in LDs and SDs.

The Plant Cell

7227563

10.1371/JOURNAL.PONE.0069872

Effect of Angle on Flow-Induced Vibrations of Pinniped Vibrissae

Two types of vibrissal surface structures, undulated and smooth, exist among pinnipeds. Most Phocidae have vibrissae with undulated surfaces, while Otariidae, Odobenidae, and a few phocid species possess vibrissae with smooth surfaces. Variations in cross-sectional profile and orientation of the vibrissae also exist between pinniped species. These factors may influence the way that the vibrissae behave when exposed to water flow. This study investigated the effect that vibrissal surface structure and orientation have on flow-induced vibrations of pinniped vibrissae. Laser vibrometry was used to record vibrations along the whisker shaft from the undulated vibrissae of harbor seals (Phoca vitulina) and northern elephant seals (Mirounga angustirostris) and the smooth vibrissae of California sea lions (Zalophus californianus). Vibrations along the whisker shaft were measured in a flume tank, at three orientations (0°, 45°, 90°) to the water flow. The results show that vibration frequency and velocity ranges were similar for both undulated and smooth vibrissae. Angle of orientation, rather than surface structure, had the greatest effect on flow-induced vibrations. Vibration velocity was up to 60 times higher when the wide, flat aspect of the whisker faced into the flow (90°), compared to when the thin edge faced into the flow (0°). Vibration frequency was also dependent on angle of orientation. Peak frequencies were measured up to 270 Hz and were highest at the 0° orientation for all whiskers. Furthermore, CT scanning was used to quantify the three-dimensional structure of pinniped vibrissae that may influence flow interactions. The CT data provide evidence that all vibrissae are flattened in cross-section to some extent and that differences exist in the orientation of this profile with respect to the major curvature of the hair shaft. These data support the hypothesis that a compressed cross-sectional profile may play a key role in reducing self-noise of the vibrissae.

PLOS ONE

37048146

10.1016/J.CUB.2012.10.045

Pygmy mole crickets jump from water

Summary Animals that live or repeatedly alight on the surface of water often need to escape from predators or return to land. We show that flightless pygmy mole crickets use a new strategy to jump rapidly from water. Their powerful hind legs are moved so quickly that they penetrate the surface and as they move through the water, unique arrays of spring-loaded paddles and spurs fan out to increase surface area. This enables these insects to propel a large volume of water downwards in a laminar flow, so that they are launched upwards into the air.

Current Biology

43048819

10.1038/NCHEMBIO0107-15

Fighting toxic copper in a bacterial pathogen.

A copper-responsive transcriptional repressor with an unusual DNA binding fold has been identified that represents the founding member of an extensive new family of bacterial transcriptional regulators.

Nature Chemical Biology

7750411

10.1242/JEB.01744

The aerodynamic effects of wing–wing interaction in flapping insect wings

SUMMARY We employed a dynamically scaled mechanical model of the small fruit fly Drosophila melanogaster (Reynolds number 100–200) to investigate force enhancement due to contralateral wing interactions during stroke reversal (the `clap-and-fling'). The results suggest that lift enhancement during clap-and-fling requires an angular separation between the two wings of no more than 10–12°. Within the limitations of the robotic apparatus, the clap-and-fling augmented total lift production by up to 17%, but depended strongly on stroke kinematics. The time course of the interaction between the wings was quite complex. For example, wing interaction attenuated total force during the initial part of the wing clap, but slightly enhanced force at the end of the clap phase. We measured two temporally transient peaks of both lift and drag enhancement during the fling phase: a prominent peak during the initial phase of the fling motion, which accounts for most of the benefit in lift production, and a smaller peak of force enhancement at the end fling when the wings started to move apart. A detailed digital particle image velocimetry (DPIV) analysis during clap-and-fling showed that the most obvious effect of the bilateral `image' wing on flow occurs during the early phase of the fling, due to a strong fluid influx between the wings as they separate. The DPIV analysis revealed, moreover, that circulation induced by a leading edge vortex (LEV) during the early fling phase was smaller than predicted by inviscid two-dimensional analytical models, whereas circulation of LEV nearly matched the predictions of Weis-Fogh's inviscid model at late fling phase. In addition, the presence of the image wing presumably causes subtle modifications in both the wake capture and viscous forces. Collectively, these effects explain some of the changes in total force and lift production during the fling. Quite surprisingly, the effect of clap-and-fling is not restricted to the dorsal part of the stroke cycle but extends to the beginning of upstroke, suggesting that the presence of the image wing distorts the gross wake structure throughout the stroke cycle.

The Journal of Experimental Biology

6707424

10.1098/RSPB.2010.0604

Harnessing disorder: onychophorans use highly unstructured proteins, not silks, for prey capture

Onychophora are ancient, carnivorous soft-bodied invertebrates which capture their prey in slime that originates from dedicated glands located on either side of the head. While the biochemical composition of the slime is known, its unusual nature and the mechanism of ensnaring thread formation have remained elusive. We have examined gene expression in the slime gland from an Australian onychophoran, Euperipatoides rowelli, and matched expressed sequence tags to separated proteins from the slime. The analysis revealed three categories of protein present: unique high-molecular-weight proline-rich proteins, and smaller concentrations of lectins and small peptides, the latter two likely to act as protease inhibitors and antimicrobial agents. The predominant proline-rich proteins (200 kDa+) are composed of tandem repeated motifs and distinguished by an unusually high proline and charged residue content. Unlike the highly structured proteins such as silks used for prey capture by spiders and insects, these proteins lack ordered secondary structure over their entire length. We propose that on expulsion of slime from the gland onto prey, evaporative water loss triggers a glass transition change in the protein solution, resulting in adhesive and enmeshing thread formation, assisted by cross-linking of complementary charged and hydrophobic regions of the protein. Euperipatoides rowelli has developed an entirely new method of capturing prey by harnessing disordered proteins rather than structured, silk-like proteins.

Proceedings of The Royal Society B: Biological Sciences

128730983

10.1029/2002JB002326

Permeability fluctuations in heterogeneous networks with different dimensionality and topology

[1] The purpose of this work was to relate the spatial fluctuations and scaling properties of the transport properties of porous rocks to their underlying pore geometry. Our approach was to numerically simulate flow through networks of pipes with randomly prescribed radii. The permeability k and inverse formation factor 1/F were calculated in a large number of network realizations of varying size and degree of heterogeneity (i.e., the width of the pipe radius distribution). We generally observed a large decrease of the ensemble arithmetic averages of k and 1/F with increasing network size (i.e., negative scale effect). Conversely, the ensemble geometric averages showed a moderate positive scale effect in three-dimensional simple cubic networks. We also found that in networks smaller than 32 × 32 or 10 × 10 × 10, the ensemble standard deviations of k and 1/F had a power law dependence on network size (defined as the total number of pipes) with an exponent α varying from −0.5 in homogeneous networks to large negative values depending on lattice topology in highly heterogeneous ones (−α increased with increasing lattice connectiveness, i.e., with coordination number). Thus at small scales the network transport properties were characterized by a nonuniversal power law scaling. At larger scales we observed a transition to a presumably “universal” power law scaling with an exponent equal to −0.5 independently on the degree of heterogeneity, dimensionality and lattice topology. Comparing our results to published experimental data, we found a good agreement, except in cases where we suspect that the small-scale measurements suffered a significant bias (indicated by non-nested distributions at increasing scales). We speculate that the strong positive scale effect generally observed in nature is also caused by sampling bias at small scales.

Journal of Geophysical Research

84197221

10.1093/ICB/24.1.85

Elastic Energy Stores in Running Vertebrates

Large mammals save much of the energy they would otherwise need for running by means of elastic structures in their legs. Kinetic and potential energy, lost at one stage of a stride, is stored temporarily as elastic strain energy and returned later in an elastic recoil. At high speeds, men and kangaroos seem to save in this way more than half the metabolic energy they would otherwise need for locomotion. It is shown by means of a generalized model that muscles and tendons could both be important as elastic energy stores. Analysis of films and force records of kangaroos hopping shows that strain energy stored while the feet are on the ground must be stored mainly distal to the knee. The principal muscles there have short fibres, and most of the storage must be in tendons. Investigation of camels shows that tendons in the feet, distal to the ankle and wrist, are especially important. The scope for elastic storage while the feet are off the groundis also considered. Though the evidence presented in this paper comes mainly from a few species, the conclusions presumably apply to large mammals in general.

Integrative and Comparative Biology

29713285

10.2174/187152607780090702

Human defensins: turning defense into offense?

Defensins are a family of antimicrobial cationic peptides that act as a rapid response force against microbial invasion in a wide range of organisms, including plants, insects, animals and humans. In humans, defensins are produced predominantly by leukocytes and epithelial cells and are an important factor of innate immunity. In addition to their major role as natural antibiotics, defensins are increasingly recognized as signaling molecules in adaptive immunity and aberrant defensin expression has been associated with infectious diseases. In this review, we discuss the role of human defensins in relation to infectious disease and the possibility of novel defensin-based therapeutic approaches.

Infectious disorders drug targets

37757144

10.1007/BF01279256

Interaction of two myosins with microfilaments causes locomotion inLabyrinthula sp.

SummaryCytoskeleton elements of aLabyrinthula isolate from the Falkland Islands were studied. The most important characteristic of the genusLabyrinthula is a colourless branched plasmatic network of pseudopodia-like tubes with sliding spindle-shaped uninuclear plasma portions (cell bodies). After fluorescent staining tubulin appears to be uniformly and diffusely distributed throughout the whole network and to form a reticulate structure in the cell bodies. The inhibitor colchicine has no influence on the sliding motility of the cell bodies nor on the movement of the network. Actin is frequently found in the network, partly in the form of microfilament bundles, which are longitudinally arranged. Actin is also present in the cortical region of cell bodies, or of cell body groups. It was difficult to distinguish single cell bodies within groups by fluorescence. The inhibitors cytochalasin B and D stop the movement of cell bodies and network. Myosin is present in the cortical region of each cell body, and the central portions of each individual cell body contain accumulations of this protein. We could not observe any fluorescence in the network after myosin staining with the antibodies we used. An actin-myosin complex is probably responsible for the sliding movement of cell bodies in the Labyrinthula network, because actin is found in the pseudopodia-like tubes, and the cortex of the cell bodies is rich in actin and myosin. This actin-myosin complex seems to differ from another actin-myosin complex that has been postulated to be responsible for the locomotion of pseudopodia-like tubes. We propose that two actin-myosin complexes exist. One of them is responsible for locomotory phenomena of the network, and the second for cell body sliding in the pseudopodia-like tubes. In each case the myosin is probably anchored in the inner matrix membrane of the pseudopodia-like tubes. A model for actin-myosin interaction inLabyrinthula spp. is presented.

Protoplasma

7297469

10.1016/J.JCIS.2007.02.049

Why do pigeon feathers repel water? Hydrophobicity of pennae, Cassie-Baxter wetting hypothesis and Cassie-Wenzel capillarity-induced wetting transition.

Wetting of pigeon feathers has been studied. It was demonstrated that the Cassie-Baxter wetting regime is inherent for pigeon pennae. The water drop, supported by network formed by barbs and barbules, sits partially on air pockets. Small static apparent angle hysteresis justifies the Cassie-Baxter wetting hypothesis. A twofold structure of a feather favors large contact angles and provides its water repellency. Cassie-Wenzel transition has been observed under drop evaporation, when drop radius becomes small enough for capillarity-induced water penetration into the protrusions, formed by barbules.

Journal of Colloid and Interface Science