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At least 883 records · Page 49Linked to original sources
PubMed1985

Relationships between spider constructs in phobics.

An index of tight construing was derived from a Kelly grid in which the elements were spiders. This index, the coefficient of concordance, corresponds to the average correlation between constructs. Concordance was significantly higher in spider phobics than controls, in line with the hypothesis that emotional disorders are associated with higher correlations between symptom-related constructs (i.e. 'tight' construing). Desensitization, though it reduced phobic anxiety, had no effect on concordance.

Adult↗
PubMed1983

Effects of a spider toxin on the glutaminergic synapse of lobster muscle.

We studied the effect of neurotoxin (JSTX) separated from spider venom on the lobster neuromuscular junction. JSTX selectively suppressed excitatory post-synaptic potentials (e.p.s.p.s) without affecting the inhibitory post-synaptic potentials (i.p.s.p.s). The effect of JSTX was dose-dependent. The threshold dose for suppressing e.p.s.p.s corresponded to a small fraction of the toxin amount in a venom gland. At high concentration, JSTX irreversibly blocked e.p.s.p.s. The reduction in amplitude of extracellularly recorded e.p.s.p.s after JSTX application followed an exponential time course. The rate of suppression increased proportionally with the toxin concentration. JSTX blocked the glutamate potential in the post-synaptic membrane but it failed to affect the aspartate-induced depolarization. Kainic acid potentiated the glutamate-induced depolarization but it was without effect in the presence of JSTX. Depolarization produced by quisqualic acid is suppressed by the toxin. Our results suggest that the spider venom contains specific blockers of glutamate receptors in crustacean neuromuscular junctions.

Animals↗
PubMedDate not supplied

Principal dynamic mode analysis of nonlinear transduction in a spider mechanoreceptor.

The nonlinear dynamics of the mechanoelectrical transduction in an arthropod mechanoreceptor (cuticular slit sense organ of the spider Cupiennius salei) were studied using Volterra kernel measurements and the recently proposed method of principal dynamic modes. Since mechanoreceptors must operate with sufficient gain sensitivity to rapidly varying displacement stimuli over a broad bandwidth and for a wide range of amplitudes, the experimental data were generated by applying pseudorandom broadband mechanical displacements of various mean levels to the cuticular slits. The recorded response data were intracellular current and potential. The purpose of this paper is to demonstrate the use of the principal dynamic mode (PDM) methodology in elucidating the nonlinear dynamics of a spider mechanoreceptor. The results obtained demonstrate that two PDMs suffice to provide a complete nonlinear dynamic model of this insect mechanoreceptor. The first PDM resembles the first-order kernel and has a low pass characteristic (position dependent), while the second PDM has a high-pass characteristic (velocity-dependent) and resides entirely in the second-order kernel (nonlinear adaptation). This study may serve as an example of the proper use of this new methodology for the analysis of nonlinear physiological systems.

Animals↗
PubMed2000

Molecular architecture and evolution of a modular spider silk protein gene.

Spider flagelliform silk is one of the most elastic natural materials known. Extensive sequencing of spider silk genes has shown that the exons and introns of the flagelliform gene underwent intragenic concerted evolution. The intron sequences are more homogenized within a species than are the exons. This pattern can be explained by extreme mutation and recombination pressures on the internally repetitive exons. The iterated sequences within exons encode protein structures that are critical to the function of silks. Therefore, attributes that make silks exceptional biomaterials may also hinder the fixation of optimally adapted protein sequences.

Amino Acid Motifs↗
PubMed1976

Heart rate in spiders: influence of body size and foraging energetics.

Resting heart rates in 18 species of spiders as determined by a cool laser transillumination technique range from 9 to 125 beats per minute. Cardiac frequencies obtained in this fashion may readily serve as a measure of standard rates of metabolism. A spider's resting heart rate is a function of body size and of foraging energetics.

Animals↗
PubMed1995

On the mechanism of homologous synapsis in lycosid spiders.

Lycosid spiders have 13 pairs of telocentric chromosomes and 2 nonhomologous sex chromosomes in males. At leptotene, the kinetochore ends are attached to the nuclear envelope via thickened attachment plaques. Homologous synapsis begins at the attachment plaques and proceeds zipper-like through the length of the synaptonemal complex. We have tested whether or not this simple form of homologous synapsis is obligatory by inducing reciprocal translocations. Since we find many irradiated cells with quadrivalents at diakinesis-prometaphase and metaphase I, clearly a backup system exists that can bring together homologous segments disparate from each other in the nucleus. This mechanism apparently does not depend on end-initiated synapsis. Furthermore, we have found in previous studies that wolf spider bivalents are always unichiasmate, with either proximally or distally placed chiasmata. Since many chain quadrivalents, but no ring quadrivalents, were seen in this study, crossing over and chiasma placement obey a different set of rules when homologous segments are switched between chromosomes.

Animals↗
PubMed1995

Effects of a spider toxin and its analogue on glutamate-activated currents in the hippocampal CA1 neuron after ischemia.

1. We studied the effects of polyamine toxins derived from a spider venom on CA1 pyramidal neurons in gerbil hippocampal slices by patch-clamp recording. Joro spider toxin (JSTX) and its synthetic analogue, 1-naphthyl acetyl spermine (Naspm), which are known to block non-N-methyl-D-aspartate (non-NMDA) receptor in a subunit specific manner, were used. 2. Naspm depressed the excitatory postsynaptic currents (EPSCs) mediated by non-NMDA receptor channels. A further reduction of EPSCs occurred with addition of 6-cyano-7-nitroquin-oxaline-2,3- dione (CNQX). Conversely, when CNQX was applied first, no further depression of EPSCs occurred on addition of Naspm, indicating that Naspm blocks a fraction of the CNQX-sensitive non-NMDA-receptor-mediated currents. 3. After ischemia, the time course of EPSCs of CA1 pyramidal neurons was slowed and Naspm depressed the slow EPSCs more strongly than those in control neurons. 4. Analysis of single-channel currents by outside-out patch-clamp recording from ischemic CA1 neurons revealed that Naspm blocked a subpopulation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate- and kainate-induced single-channel currents. 5. Because the EPSCs in CA1 neurons after ischemia are mediated by Ca(2+)-permeable non-NMDA receptor-mediated conductances, the present results indicate that Naspm and JSTX are effective at blocking abnormal EPSCs that may induce Ca2+ accumulation leading to delayed neuronal death after transient ischemic insult.

Animals↗
PubMed1996

Threshold for detecting temperature changes in a spider thermoreceptor.

1. The threshold for detecting a change in temperature of a warm receptor in the wandering spider Cupiennius salei was determined by means of its frequency-dependent noise. To accomplish this, the warm receptor was regarded as a linear system consisting of two components, an amplifier (gain of the frequency response) and noise at its input added to the temperature stimulus (input noise density). 2. The frequency response was investigated with sinusoidal temperature modulations at frequencies between 0.05 and 12.8 Hz. The gain increased by 3.5 dB/octave in the frequency range between 0.05 and 6.4 Hz, from 0.19 to 3.1 degrees C-1. However, at the highest frequency, 12.8 Hz, the gain was reduced. 3. The noise density of the warm receptor was measured by the root-mean-square noise amplitude of the gain. The output noise density of the warm receptor, which describes the noise density of the gain, was constant at approximately 0.2 Hz-0.5 in the 0.05 to 6.4 Hz range, and increased at higher frequencies. The input noise density, given by the ratio of output noise density to gain, decreased by -2.7 dB/octave between 0.05 and 6.4 Hz, from 1.1 to 0.12 degrees C*Hz-0.5. 4. To define the threshold for detection of temperature changes from the input noise density, the energy of the threshold was equated to the energy of the noise. Assuming a signal-to-noise ratio of 1 and an upper limiting frequency of 10 Hz, the threshold estimated for the wandering spider Cupiennius ranges from 0.6 to 0.08 degrees C, depending on whether the inputs from only 1 or all 70 warm receptors of the 10 tarsal organs are combined.

Acoustic Stimulation↗
PubMed2004

Changes in hematological, hemostatic and biochemical parameters induced experimentally in rabbits by Loxosceles gaucho spider venom.

Human accidents caused by Loxosceles spiders may result in local dermal necrosis and, in some cases, severe systemic reactions - such as intravascular hemolysis, disseminated intravascular coagulation (DIC), renal failure and death. Since many aspects of envenomation by Loxosceles spiders remain unclear, we studied the hematological and hemostatic responses induced by the i.d. injection of 10 microg/kg Loxosceles gaucho venom in rabbits. For this purpose, total blood cell count, platelet function, coagulation tests and biochemical parameters were analysed at 3, 24, 48, 72 and 120 hours after venom administration. Thrombocytopenia and leukopenia were noted at 3 and 24 hours. Histopathological analysis of the skin lesion, performed at 24 hours after venom administration, showed a massive presence of leukocytes and platelets, hemorrhage and thrombus formation at the injection site. At 72 and 120 hours, neutrophilic leukocytosis and thrombocytosis were observed. Platelet hyperaggregation was noticeable at 48 and 72 hours. Haptoglobin and fibrinogen levels were elevated early and remained in high levels over time. Significant increases in coagulation factors V, VII, VIII, IX, X and XI were noted at 120 hours. The results showed that neither intravascular hemolysis nor DIC occurred. However, the early onset of thrombocytopenia and leukopenia are important findings that may be related to dermal necrosis formation during loxoscelism.

Animals↗
PubMed2003

Adhesion measurements on the attachment devices of the jumping spider Evarcha arcuata.

The feet of the jumping spider Evarcha arcuata attach to rough substrates using tarsal claws. On smooth surfaces, however, attachment is achieved by means of a claw tuft, the scopula. All eight feet bear a tarsal scopula, which is equipped with setae, these again being covered by numerous setules. In E. arcuata, an estimated 624,000 setules, with a mean contact area of 1.7 x 10(5) nm(2), are present. The spider's entire contact area thus totals 1.06 x 10(11) nm(2). Adhesion to the substrate does not depend on the secretion of an adhesive fluid. Analysis via atomic force microscopy (AFM) shows that a single setule can produce an adhesive force (F(a)) of 38.12 nN perpendicular to a surface. Consequently, at a total F(a) of 2.38 x 10(-2) N and a mean body mass of 15.1 mg, a safety factor (SF; F(a)/F(m), where F(m) is weight) of 160 is achieved. Tenacity (tau(n); F(a)/A, where A is area of contact) amounts to 2.24 x 10(5) N m(-2).

Adhesiveness↗
PubMed2003

van der Waals and hygroscopic forces of adhesion generated by spider capture threads.

Cribellar thread is the most primitive type of sticky prey capture thread found in aerial spider webs. Its outer surface is formed of thousands of fine fibrils that issue from a cribellum spinning field. The fibrils of primitive cribellar thread are cylindrical, whereas those of derived threads have nodes. Cribellar threads snag on insect setae but also adhere to smooth surfaces. A previous study showed empirically that cylindrical fibrils use only van der Waals forces to stick to smooth surfaces, as their stickiness is the same under different humidity. By contrast, noded fibrils are stickier under high humidity, where they are presumed to adsorb atmospheric water and implement hygroscopic (capillary) adhesion. Here, we model thread stickiness according to these two adhesive mechanisms. These models equate stickiness with the force necessary to overcome the adhesion of fibril contact points in a narrow band along each edge of the contact surface and to initiate peeling of the thread from the surface. Modeled and measured thread stickiness values are similar, supporting the operation of the hypothesized adhesive forces and portraying an important transition in the evolution of spider threads. Cribellar threads initially relied only on van der Waals forces to stick to smooth surfaces. The appearance of fibril nodes introduced hydrophilic sites that implemented hygroscopic force and increased thread stickiness under intermediate and high humidity.

Adhesiveness↗
PubMed2005

The effect of spinning forces on spider silk properties.

A new forced silking procedure has been developed that allows measurement of the low forces involved in the silking process and, subsequently, retrieval and tensile testing of the samples spun at the measured silking forces. A strong correlation between silking force and tensile behaviour of spider silk has been established. Fibres spun at high silking force--compared with the conventional yield stress--are stiff and show stress-strain curves previously found in forcibly silked fibres. By contrast, fibres spun at low and very low silking forces are more compliant, and their tensile behaviour corresponds to that of fibres naturally spun by the spider or to fibres subjected to maximum supercontraction, respectively. It has also been found that samples retrieved from processes with significant variations in the silking force are largely variable in terms of force-displacement curves, although reproducibility improves if force is re-scaled into stress. Fibres retrieved from processes with constant silking force show similar tensile properties both in terms of force-displacement and stress-strain curves.

Animals↗
PubMed2006

The influence of anaesthesia on the tensile properties of spider silk.

In this study of the effect of anaesthesia on both the forced silking process and on the properties of the retrieved silk fibres, a monitored forced silking process enables the silking force to be measured during the whole process. Silk samples were tensile-tested and their diameters measured. Force-displacement curves and stress-strain curves were drawn. The evolution of the silking process of anaesthetized spiders is found to be complex, but it sheds light on the details of the spinning mechanism of spider silk.

Anesthetics↗
PubMed2006

Silken toolkits: biomechanics of silk fibers spun by the orb web spider Argiope argentata (Fabricius 1775).

Orb-weaving spiders spin five fibrous silks from differentiated glands that contain unique sets of proteins. Despite diverse ecological functions, the mechanical properties of most of these silks are not well characterized. Here, we quantify the mechanical performance of this toolkit of silks for the silver garden spider Argiope argentata. Four silks exhibit viscoelastic behaviour typical of polymers, but differ statistically from each other by up to 250% in performance, giving each silk a distinctive suite of material properties. Major ampullate silk is 50% stronger than other fibers, but also less extensible. Aciniform silk is almost twice as tough as other silks because of high strength and extensibility. Capture spiral silk, coated with aqueous glue, is an order of magnitude stretchier than other silks. Dynamic mechanical properties are qualitatively similar, but quantitatively vary by up to 300% among silks. Storage moduli are initially nearly constant and increase after fiber yield, whereas loss tangents reach maxima of 0.1-0.2 at the yield. The remarkable mechanical diversity of Argiope argentata silks probably results in part from the different molecular structures of fibers and can be related to the specific ecological role of each silk. Our study indicates substantial potential to customize the mechanics of bioengineered silks.

Animals↗
PubMed2006

Unraveling the mechanical properties of composite silk threads spun by cribellate orb-weaving spiders.

Orb-web weaving spiders depend upon the mechanical performance of capture threads to absorb the energy of flying prey. Most orb-weavers spin wet capture threads with core fibers of flagelliform silk. These threads are extremely compliant and extensible due to the folding of their constituent proteins into molecular nanosprings and hydration by a surrounding coating of aqueous glue. In contrast, other orb-weavers use cribellate capture threads, which are composite structures consisting of core fibers of pseudoflagelliform silk surrounded by a matrix of fine dry cribellar fibrils. Based on phylogenetic evidence, cribellate capture threads predate the use of viscid capture threads. To better characterize how pseudoflagelliform and cribellar fibrils function, we investigated the mechanical performance of cribellate capture threads for three genera of spiders (Deinopis, Hyptiotes and Uloborus). These taxa spin very diverse web architectures, ranging from complete orbs to evolutionarily reduced triangle webs and cast nets. We found that the pseudoflagelliform core fibers of these webs were stiffer and stronger, but also less extensible, than flagelliform silk. However, cribellate capture threads achieved overall high extensibilities because the surrounding cribellar fibrils contributed substantially to the tensile performance of threads long after the core pseudoflagelliform fibers ruptured. In the case of Deinopis capture threads, up to 90% of the total work performed could be attributed to these fibrils. These findings yield insight into the evolutionary transition from cribellate to viscid capture threads.

Animals↗
PubMed2001

Bimodal breathing in jumping spiders: morphometric partitioning of the lungs and tracheae in Salticus scenicus (Arachnida, Araneae, Salticidae).

In jumping spiders, both the book lungs and the tracheal system are well-developed. The tracheal system consists of four thick primary tracheae that branch into small secondary tracheae, some of them ending in the opisthosoma and others entering the prosoma. We used stereological morphometric methods to investigate the morphological diffusing capacity of the lungs and of the walls of the secondary tracheae ('lateral diffusing capacity') of two groups of Salticus scenicus with mean body masses of 2.69 mg (group A) and 5.28 mg (group B). The thickness of the gas-exchange epithelium of the lungs was 0.164 microm (group A) and 0.186 microm (group B) for the total diffusion barrier. The secondary tracheae were divided arbitrarily into seven classes according to their inner diameter (1-7 microm). The diffusion barriers of the tracheal walls tend to be thinnest (0.17 and 0.18 microm) for the smallest tracheae, the walls of the other tracheal classes having approximately the same thickness of diffusion barrier (0.24-0.32 microm). The calculated oxygen-diffusing capacity (D(O(2))) for the lungs was 16.4 microl min(-1) g(-1) kPa(-1) for group A and 12 microl min(-1) g(-1) kPa(-1) for group B; the D(O(2)) of the walls of all secondary tracheae was 5.91 microl min(-1) g(-1) kPa(-1) for group A animals and 6.63 microl min(-1) g(-1) kPa(-1) for group B animals. Our results are consistent with the hypothesis that the tracheal system plays an important role in gas exchange in jumping spiders. Resting and low-activity oxygen consumption rates can be met by the lungs or the tracheae alone, while high oxygen demands can be met only if both respiratory systems are working together. Tracheae entering the prosoma have only 4-10 % of the total tracheal diffusing capacity, thus providing sufficient oxygen for the nervous system but not being able to prevent muscle fatigue. The similar thickness of the walls of all tracheal classes is consistent with the hypothesis that the secondary tube tracheae function as 'tracheal lungs', supplying the haemolymph and organs by lateral diffusion.

Animals↗
PubMed2002

Influence of cues from the anterior medial eyes of virtual prey on Portia fimbriata, an araneophagic jumping spider.

Portia fimbriata from Queensland, Australia, is a jumping spider (Salticidae) that preys on other spiders, including other salticids. Cryptic stalking (palps retracted, walking very slowly and freezing when faced) is a prey-specific tactic deployed exclusively against salticid prey. Using vision alone, P. fimbriata discriminates salticid from non-salticid prey, with the prey salticid's large anterior median (AM) eyes providing critical cues. Here, using computer-rendered virtual three-dimensional lures, we clarify experimentally some of the specific optical cues from AM eyes that influence the behaviour of P. fimbriata. Control lures were based on Jacksonoides queenslandicus, the salticid upon which P. fimbriata most commonly preys in nature. Experimental lures were modified to isolate specific combinations of AM eye features. For presentation to P. fimbriata, lures were projected on a small screen positioned in front of a web-covered platform. Each individual P. fimbriata was tested once with a control lure and once with a lure on which some AM eye feature had been altered. P. fimbriata was affected by the presence-versus-absence of AM eyes, by the size and shape of these eyes and by AM eye position. Horizontal position on the face of a single AM eye had no discernible influence on whether P. fimbriata initiated cryptic stalking, but reduced how often P. fimbriata froze when faced by the prey. The implications of the findings are discussed in relation to perceptual processes underlying the predatory strategy of P. fimbriata.

Animals↗
PubMed1976

Haemocyanins in spiders, III. Chemical and physical properties of the proteins in Dugesiella and Cupiennius blood.

The haemolymph of the tarantulas, Dugesiella (Eurypelma) californica and Dugesiella (Eurypelma) helluo contains high molecular weight haemocyanin (80-82% of total blood proteins) and a second protein not related to haemocyanin (18-20%). In the Lycosid spider, Cupiennius salei, haemocyanin (75% of total blood protein) occurs in two states of association. The haemocyanins were isolated by ultracentrifugation, gel filtration, isoelectric focusing, or preparative gel electrophoresis. Their sedimentation constants are 36.7 S (both tarantulas), 23.4 S and 15.9 S (Cupiennius). After alkaline dissociation, polypeptides sedimenting at 5.8 S (D. californica) and 4.7 S (Cupiennius) were obtained. The molecular weight of the intact functional subunit is (by sedimentation equilibrium) 70 300 (D. californica) and 69 900 (Cupiennius). Copper analysis results in closely similar values. By sodium dodecylsulphate gel electrophoresis, molecular weights of 71 000 (D. californica), 72 000 (Cupiennius) and 74 000 (D. helluo) were obtained. Denaturation with various agents did not lead to smaller polypeptides. The amino acid composition of the haemocyanins was determined (Table 1). The amino end group is blocked. The haemocyanins contain 1.2-1.5% of neutral carbohydrates and 0.3-0.5% of glucosamine (possibly acetylated). The neutral carbohydrates were identified with glucose, mannose, fucose, and arabinose, glucose being the dominant species. Neuraminic acid was not detected. The haemocyanins of the three species cannot be distinguished by their carbohydrate moieties, while there is a significant difference in amino acid composition between tarantula and Cupiennius haemocyanins. The second, non-respiratory protein isolated from spider blood sediments with 16.1 S (Dugesiella) or 15.9 S (Cupiennius). Its isoelectric point is at pH 5.5 It is stable in weakly alkaline solutions but can be denatured to yield polypeptide chains with molecular weights of 95 000 and 110 000. The amino acid composition is reported. As in the haemocyanins, the N-terminus is blocked. The carbohydrate content is 0.9%, glucose being the only sugar identified.

Amino Acids↗