Protection of the hermit crab Pagurus pollicaris say from predators by hydroid-colonized shells

Only one study has shown that a hydroid-colonized gastropod shell was a deterrent to predation on hermit crabs. In the present study, the hydroid-colonized shell protected the hermit crab Paguruspollicaris Say from the shell-crushing stone crab Menippe mercenaria (Say) and the non-shell-crushing octopus Octopus joubini Robson. The shell-crushing calico crab Hepatus epheliticus (Johansson) was not deterred, however, by a hydroid-colonized shell.     

Avoidance of drilled gastropod shells by the hermit crab Pagurus longicarpus at Nahant, Massachusetts

Most hermit crabs depend on empty gastropod shells for shelter; competition for appropriate shells is often severe. This study determined whether shells that have been drilled by naticid gastropods are suitable for occupancy by the hermit crab Pagurus longicarpus. Differences in the characteristics of empty shells and those occupied by hermit crabs were assessed at two adjacent field sites in Nahant, Massachusetts. Drilling damage was far more frequent in empty gastropod shells than in shells occupied by hermit crabs, suggesting that individuals of P. longicarpus avoid drilled shells. They did not appear to avoid shells with other forms of damage. Laboratory experiments confirmed that these hermit crabs preferentially chose intact shells over drilled shells, even when the intact shells offered were most suitable for crabs half the weight of those tested. Final shell choices were generally made within 1 h. The hermit crabs apparently discriminated between intact and drilled shells based on tactile cues, since crabs kept in the dark showed the same preference for intact shells. The hermit crabs strongly avoided, to nearly the same extent, artificially drilled shells, naturally drilled shells, and shells with holes artificially drilled on the opposite side of the shell from where they would normally be located. Possible selective forces causing P. longicarpus to show such strong behavioral avoidance of drilled shells include increased vulnerability of crabs in drilled shells to osmotic stress, predation, and eviction by conspecifics.     

Weather and the use of empty gastropod shells by arthropods

Arthropods frequently use empty snail shells as shelter or nesting sites. This study analyses the use of shells from the arid-dwelling land snail Sphincterochila candidissima (Draparnaud 1801) by arthropods in the Sierra Elvira (south-eastern Spain). Arthropods of 11 different orders occupied 15.6% of shells. Salticidae (54.6%) and Apoidea (21.3%) comprised the majority of arthropods. Shells were used primarily when environmental temperatures were lowest, suggesting that, in the Sierra Elvira, arthropods use shells to escape from the cold. Weather explained 73% of the variation in shell occupation. However, Apoidea used shells independently of weather, occupying shells as nesting chambers. These results suggest that snail shells may be important refugia and nesting sites for arthropod fauna.     

Demineralization of crab shells by chemical and biological treatments

To achieve demineralization of crab shell waste by chemical and biological treatments, lactic acid and lactic acid bacterium were applied. In 5.0 and 10% lactic acid, pH rapidly decreased from 6.8 to 4.2 and from 4.5 to 2.4 at day 3, respectively, and thereafter the pH remained at an almost constant level. In a 10% lactic acid bacterium inoculum, pH lowered to 4.6 at day 5. Relative residual ash content rapidly decreased to 49.1 and 16.4% in 5 and 10% lactic acid treatments, respectively, for the initial 12 h. In 2.5, 5 and 10% lactic acid bacterium inoculums, relative residual ash content rapidly decreased to 55.2, 40.9 and 44.7%, respectively, on the first day. Residual dry masses were 76.4, 67.8 and 46.6% in 2.5, 5 and 10% lactic acid treatments, respectively, for the initial 12 h. After a one-time exchange of the lactic acid solution, in the 5.0% lactic acid treatment, residual dry mass rapidly decreased from 66.0 to 41.4%. In 2.5, 5 and 10% lactic acid bacterium inoculums, residual dry masses decreased to 67.6, 57.4 and 59.6% respectively, on the first day. Protein contents after demineralization ranged from 51.3–54.7% in the chemical treatments and decreased to 32.3% in the lactic acid fermentation process. A negative relationship was shown between pH and demineralization rate in lactic acid and lactic acid bacterium treatments. These results suggest that lactic acid fermentation can be an alternative for demineralization of crab shells, even though the rate and efficiency of the demineralization is lower than the chemical treatment.     

Effect of bone quality on the forces generated by compression screws.

Internal fixation of the fractured scaphoid bone is used to promote union between bone fragments and to decrease wrist immobilization. Headless screws are commonly used because they minimize interference with articular surfaces and reduce tissue irritation and immobilization. In the present experiment, compressive force was measured as a function of bone quality for two headless screw types, the Herbert and the Acutrak. Forty-seven cylindrical samples of cancellous bone were prepared from fresh, previously frozen human cadaveric distal femora. The compressive forces generated as the screws were advanced into the specimens were measured and correlated to the specimens' bone mineral density (BMD) and density. Over the range tested, the average compressive force for the Acutrack screw was approximately 42% higher than that of the Herbert. Statistical significance, however, could not established because of the low statistical power of the test due to the inherent spread in the data. For the Acutrak screw, force was best fit to BMD and to density by second-order polynomials. Regression analysis indicated that similar correlations did not exist between force and BMD or between force and density for the Herbert screw. The correlation shown by the Acutrak screw indicates that it may be a more predictable as well as more effective system and therefore there may be some advantage in selecting this system. Furthermore, results suggest that the Acutrak screw generates greater forces with increasing bone density and could be more effective for a younger population.     

Behavioural evidence for visual recognition of predators by the mangrove climbing crab Sesarma leptosoma

The climbing crab Sesarma leptosoma colonizes the mangrove roots and canopy of East African mangrove swamps, an intricate three-dimensional habitat in which it orients itself visually. To ascertain if vision helps this tree crab to detect dangers such as predators, we used dummy objects: (1) a preserved specimen of its predator, the crab Epixanthus dentatus in its typical ambush posture; (2) a piece of wood with real E. dentatus claws attached to it, the same size as, and painted to resemble (to the human eye), this predator; and (3) a piece of wood the same size and colour as a live crab but without claws. When these dummies were presented to migrating S. leptosoma in the field, they stopped their normal migratory flow only when they were able to see the open claws of the predator. Thus S. leptosoma showed a considerable ability to perceive shape, being able to distinguish motionless objects of different shapes but similar size and to associate the detected shapes with the presence of danger.     

Estimation of the forces generated by the thigh muscles for transtibial amputee gait

The forces generated by the muscles with origin on the human femur play a major role in transtibial amputee gait, as they are the most effective of the means that the body can use for propulsion. By estimating the forces generated by the thigh muscles of transtibial amputees, and comparing them to the forces generated by the thigh muscles of normal subjects, it is possible to better estimate the energy output needed from prosthetic devices. The purpose of this paper is to obtain the forces generated by the thigh muscles of transtibial amputees and compare these with forces obtained from the same muscles in the case of normal subjects. Two transtibial amputees and four normal subjects similar in size to the amputees were investigated. Level ground walking was chosen as the movement to be studied, since it is a common activity that most amputees engage in. Inverse dynamics and a muscle recruitment algorithm (developed by AnyBody Technology^®) were used for generating the muscle activation patterns and for computing the muscle forces. The muscle forces were estimated as two sums: one for all posterior muscles and one for the anterior muscles, based on the position of the muscles of the thigh relative to the frontal plane of the human body. The results showed that a significantly higher force is generated by the posterior muscles of the amputees during walking, leading to a general increase of the metabolic cost necessary for one step.     

A novel method for measuring tension generated in stress fibers by applying external forces

The distribution of contractile forces generated in cytoskeletal stress fibers (SFs) contributes to cellular dynamic functions such as migration and mechanotransduction. Here we describe a novel (to our knowledge) method for measuring local tensions in SFs based on the following procedure: 1), known forces of different magnitudes are applied to an SF in the direction perpendicular to its longitudinal axis; 2), force balance equations are used to calculate the resulting tensions in the SF from changes in the SF angle; and 3), the relationship between tension and applied force thus established is extrapolated to an applied force of zero to determine the preexisting tension in the SF. In this study, we measured tensions in SFs by attaching magnetic particles to them and applying known forces with an electromagnetic needle. Fluorescence microscopy was used to capture images of SFs fluorescently labeled with myosin II antibodies, and analysis of these images allowed the tension in the SFs to be measured. The average tension measured in this study was comparable to previous reports, which indicates that this method may become a powerful tool for elucidating the mechanisms by which cytoskeletal tensions affect cellular functions.     

Elastic and damping forces generated by confined arrays of dynamic microtubules

In addition to serving as structural elements and as tracks for motor proteins, microtubules use chemical energy derived from the hydrolysis of GTP to generate forces when growing and shrinking. These forces are used to push or pull on organelles such as chromosomes and the mitotic spindle. If an array of microtubules grows out from a nucleation site and is confined by the periphery of the cell, pushing and pulling forces can give rise to interesting collective phenomena. In this paper, I show that pushing forces center the array provided that the microtubules are dynamic in the sense that they switch from pushing to shrinking after reaching the periphery. Microtubule dynamics of free ends is neither necessary nor sufficient for centering. Buckling can augment the centering force. For small displacements and velocities, the array can be modeled very simply as a damped spring. The dynamic stiffness of the array is orders of magnitude smaller than its static stiffness, and the relaxation time is on the order of the time that it takes for a microtubule to grow from the center to the periphery. Replacement of a dynamic polymer array with an equivalent mechanical circuit provides a bridge between molecular and cellular mechanics.     

A potential artifact generated by pelleting viral particles during preparative ultracentrifugation

Pelleting in an ultracentrifuge produces fundamental changes in the structural and functional characteristics of some types of subviral particles of reovirus. Attention is drawn to this phenomenon as a possible source of artifact in experiments where pelleting of bioparticles is employed in the preparative procedure, as is common practice in a wide variety of studies.     

Microstructural details in shells of the gastropod genera Carychiella and Carychium of the Middle Miocene

Microstructural details are revealed via scanning electron microscopy (SEM) in two carychiid species from the early Middle Miocene of Styria, SE Austria. The protoconchs of the shells of Carychiella eumicrum (Bourguignat 1857) and Carychium gibbum (Sandberger 1875) show different types of microstructure on the embryonic shell during ontogeny. Total, superficial punctate structure on the shell of Carychiella eumicrum contrasts with the protoconch–teleoconch demarcation (p/t boundary) observed on the protoconch of Carychium gibbum. Both species exhibit aragonitic microstructure. Diagenetic effects, prismatic, homogeneous and crossed lamellar microstructures are detectible in both species. Rheomorphic folding and dense pitting within the columella of Carychiella eumicrum suggest a structure–function relationship for tensile strength and bulk weight reduction in carychiid snails. We hypothesize that total superficial pitting on the shell of C. eumicum, seen here for the first time in the Carychiidae, suggests paedomorphosis as a life‐history strategy to palaeoecological conditions of the Rein Basin during the early Middle Miocene.     

Bioerosion of gastropod shells: with emphasis on effects of coralline algal cover and shell microstructure

Organisms boring into fifty nine species of gastropod shells on reefs around Guam were the bryozoan Penetrantia clionoides; the acrothoracian barnacles Cryptophialus coronorphorus, Cryptophialus zulloi and Lithoglyptis mitis; the foraminifer Cymbaloporella tabellaeformis, the polydorid Polydora sp. and seven species of clionid sponge. Evidence that crustose coralline algae interfere with settlement of larvae of acrothoracian barnacles, clionid sponges, and boring polychaetes came from two sources: (1) low intensity of boring in limpet shells, a potentially penetrable substrate that remains largely free of borings by virtue of becoming fully covered with coralline algae at a young age and (2) the extremely low levels of boring in the algal ridge, a massive area of carbonate almost entirely covered by a layer of living crustose corallines. There was a strong negative correlation between microstructural hardness and infestation by acrothoracian barnacles and no correlation in the case of the other borers. It is suggested that this points to a mechanical rather than a chemical method of boring by the barnacles. The periostracum, a layer of organic material reputedly a natural inhibitor of boring organisms, was bored by acrothoracican barnacles and by the bryozoan. The intensity of acrothoracican borings is shown to have no correlation with the length of the gastropod shell.     

A modified blade element theory for estimation of forces generated by a beetle-mimicking flapping wing system

We present an unsteady blade element theory (BET) model to estimate the aerodynamic forces produced by a freely flying beetle and a beetle-mimicking flapping wing system. Added mass and rotational forces are included to accommodate the unsteady force. In addition to the aerodynamic forces needed to accurately estimate the time history of the forces, the inertial forces of the wings are also calculated. All of the force components are considered based on the full three-dimensional (3D) motion of the wing. The result obtained by the present BET model is validated with the data which were presented in a reference paper. The difference between the averages of the estimated forces (lift and drag) and the measured forces in the reference is about 5.7%. The BET model is also used to estimate the force produced by a freely flying beetle and a beetle-mimicking flapping wing system. The wing kinematics used in the BET calculation of a real beetle and the flapping wing system are captured using high-speed cameras. The results show that the average estimated vertical force of the beetle is reasonably close to the weight of the beetle, and the average estimated thrust of the beetle-mimicking flapping wing system is in good agreement with the measured value. Our results show that the unsteady lift and drag coefficients measured by Dickinson et al are still useful for relatively higher Reynolds number cases, and the proposed BET can be a good way to estimate the force produced by a flapping wing system.     

Measurement of mechanical forces generated by plant P-protein aggregates (forisomes)

Mechanical forces generated by forisomes were measured using a microfabricated polymer cantilever sensor. The forces were simultaneously measured in both the longitudinal and radial directions. Sensors were fabricated from polystyrene using the sacrificial layer micromolding process. The sensor response was simulated using finite element analysis. Forces in the longitudinal direction ranged from 84 to 136 nN and forces in the radial direction were 22–61 nN. This device offers a new approach to measuring small magnitude biological forces. In addition, the ability to accurately measure forces generated by forisomes is an important step toward their implementation as functional structures in microdevices.     

Plasma membrane potential of neutrophils generated by the Na+ pump

The plasma membrane potential of human neutrophils was monitored using the anionic dye oxonol-V. The cells maintain a potential of -75 +/- 17 mV when suspended in physiological saline solutions. The cells are scarcely depolarized by extracellular K+ and the depolarization induced by the chemotactic peptide fMet-Leu-Phe is of similar magnitude for cells suspended in 5 or 155 mM K+. Neutrophils are, however, depolarized by suspension in K+-free media or after treatment with ouabain. Neutrophils catalyse Na+-H+ exchange and possess other electroneutral ion transport systems. We propose that the neutrophil membrane potential is generated by an electrogenic Na+ pump, that osmotic stability is achieved by electroneutral ion transport systems and that electrical stability is maintained by anion leakage. Similar mechanisms may also operate in other biological membranes.     

External forces and torques generated by the brachiating white-handed gibbon (Hylobates lar)

We compared the kinetics of brachiation to bipedal walking and running. Gibbons use pectoral limbs in continuous contact with their overhead support at slow speeds, but exhibit aerial phases (or ricochetal brachiation) at faster speeds. This basic interaction between limb and support suggests some analogy to walking and running. We quantified the forces in three axes and torque about the vertical axis generated by a brachiating White-handed gibbon (Hylobates lar) and compared them with bipedal locomotion. Handholds oriented perpendicular to the direction of travel (as in ladder rungs) were spaced 0.80, 1.20, 1.60, 1.72, 1.95, and 2.25 m apart. The gibbon proportionally matched forward velocity to stride length. Handhold reaction forces resembled ground reaction forces of running humans except that the order of horizontal braking and propulsion were reversed. Peak vertical forces in brachiation increased with speed as in bipedal locomotion. In contrast to bipedalism, however, peak horizontal forces changed little with speed. Gait transition occurred within the same relative velocity range as the walk-run transition in bipeds (Froude number = 0.3-0.6). We oriented handholds parallel to the direction of travel (as in a continuous pole) at 0.80 and 1.60 m spacings. In ricochetal brachiation, the gibbon generated greater torque with handholds oriented perpendicular as opposed to parallel to the direction of travel. Handhold orientation did not affect peak forces. The similarities and differences between brachiation and bipedalism offer insight into the ubiquity of mechanical principles guiding all limbed locomotion and the distinctiveness of brachiation as a unique mode of locomotion.     

A species comparison of alveolar size and surface forces

The independent roles of alveolar size and surface tension in relation to lung stability were investigated in 11 different mammalian species whose body weight ranged from 0.03 to 50 kg. This range in species provided a wide variation in subgross anatomy as well as a fourfold range in alveolar diameter. Alveolar diameter was estimated from the mean linear intercept (Lm) of fixed lungs. Quasi-static pressure-volume curves were determined in excised lungs and the percent volume remaining on deflation from total lung capacity at 30 cmH2O to 10 cmH2O (%V10) provided an index of deflation stability related to functional surfactant. Surface tension of lung extract was measured in the Wilhelmy balance, and the minimum surface tension measured provided an index of surface tension lowering capacity of surfactant. Relationships of %V10 with alveolar diameter and surface tension with alveolar diameter were examined for correlations. Our results indicated that despite a range in Lm between 31 and 133 micron (mouse to pig), %V10 did not change in proportion with Lm across species. Similarly, minimum surface tension was about the same (6.1 to 8.8 dyn/cm) across a threefold difference in alveolar diameter. These results suggest that a stable alveolar configuration is maintained by both surface and tissue forces in a complex manner yet to be analyzed.     

Variation in the spire index of some coiled gastropod shells, and its evolutionary significance.

The spire index (height/maximum diameter of shell) is a fairly adequate measure of the shape of the coiled shell of most terrestrial and freshwater gastropod shells but less so in complex marine shells with thorns, flanges and spouts. In this study, only adult free-crawling forms with several whorls, able to retract completely into the shell, are considered. In the Stylommatophora of the Western European terrestrial fauna the distribution of the spire index is markedly bimodal, the modes, with values of about 3 and about 0.5, corresponding respectively to shells with a high to very high spire (and small spire angle) and those varying from more or less globular or trochoid to very flattened and disk-like (spire angle from 60 degrees to 180 degrees). The same two modes are found in the taxonomically different terrestrial stylommatophorans of the U.S.A., and in the faunas of Puerto Rico (Caribbean) and New Caledonia (southwest Pacific). Basommatophorans also show two, rather different, modes. North American marine archaeogastropods are mainly equidimensional but with a few disk-like forms and a very few high-spired ones, marine mesogastropods are mainly high-spired but with disk-like forms, neogastropods high-spired, and relevant euthyneurans sharply bimodal, like the stylommatophorans. Fossil archaeogastropods of the Palaeozoic were much more various at first than modern forms. There is some indication that they became restricted in variety as caenogastropods became abundant, but also that the proportion of marine disk-like shells has decreased markedly since the Palaeozoic. Modes of h/d are characteristic of large taxonomic groups but not taxonomically restricted since given values may appear as specific, generic or subfamilial variants from a mode, and appear sporadically in unrelated forms. There is also no broad association between modal value and broad ecological characters. Since nearly all values do occur in some group or other, no mechanical requirement can be invoked to explain such variation. In the land Stylommatophora enough is known of the broad ecology to suggest that in extreme habitats species with very different size or shell-shape may occur together, and that generalized feeders with similar shells may show separation, ecological or geographical (but in that case, also ecological). Since different shapes of shell will have different mechanical characteristics when considered as burdens to be carried, it is suggested tentatively that they may be related to the positions in which different species normally walk and hence to their preferred feeding places. This would explain an apparent tendency for different taxonomic groups to occupy the same part of the scatter of h/d in different regions of the world, for many groups in the same region to occupy different portions of the scatter, and perhaps the apparent exclusion by caenogastropods of archaeogastropods from part of the scatter since the Palaeozoic. It is argued that the distributions discovered are explicable only by natural selection.     

A comparison of electrical and diffusion forces in the metabolism of electrolytes

Using an approximation method the electrical forces due to the metabolism of electrolytes have been compared to the ordinary diffusion forces and found negligible.