Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Spiders”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources
PubMed2006

Nonsynchronous recovery of community characteristics in island spiders after a catastrophic hurricane.

We monitored spiders on 41 Bahamian islands for 4 years before and then 4 years after the catastrophic Hurricane Floyd passed directly over the site, inundating the study islands with its storm surge. The respective recoveries of major community properties after this annihilation were far from synchronous. Before the hurricane, the species-area relation was generally strong and the slope showed no temporal trend. After the hurricane, the slope increased from near zero (7 months later) to a value about equal to its prehurricane state. The lizard effect (difference in spider abundance or species richness between islands with and without the lizard Anolis sagrei) was generally strong before the hurricane; 7 months after, the lizard effect on abundance was weak and the effect on richness had vanished. In subsequent years, the lizard effect on abundance became strong again, but the effect on species richness remained weak. The strength of the lizard effect on both abundance and richness over the 8 years was strongly positively related to the density of lizards measured on a subset of the study islands. Twelve months after the hurricane, species richness averaged over all islands rebounded to the last prehurricane value, but abundance attained only about half that value; this finding was remarkably similar to results found in an earlier study of spiders impacted by Hurricane Lili (1996) in a different Bahamian region. Nonetheless, in the next 3 years, species richness failed to increase further, part of its long-term decline at the study site.

Adaptation, Biological↗
PubMed2000

Expression patterns of hairy, even-skipped, and runt in the spider Cupiennius salei imply that these genes were segmentation genes in a basal arthropod.

There is an ongoing discussion on whether segmentation in different phyla has a common origin sharing a common genetic program. However, before comparing segmentation between phyla, it is necessary to identify the ancestral condition within each phylum. Even within the arthropods it is not clear which parts of the genetic network leading to segmentation are conserved in all groups. In this paper, we analyze the expression of three segmentation genes of the pair-rule class in the spider Cupiennius salei. Spiders are representatives of the Chelicerata, a monophyletic basic arthropod group. We find that in spider embryos, the orthologues for the Drosophila primary pair-rule genes hairy, even-skipped, and runt are expressed in stripes in the growth zone, where the segments are forming, suggesting a role for these genes in chelicerate segmentation. These data imply that the involvement of hairy, even-skipped, and runt in arthropod segmentation is an ancestral character for arthropods and is not restricted to a particular group of insects.

Animals↗
PubMed2005

Lateral gene transfer of a dermonecrotic toxin between spiders and bacteria.

MOTIVATION: Spiders in the genus Loxosceles, including the notoriously toxic brown recluse, cause severe necrotic skin lesions owing to the presence of a venom enzyme called sphingomyelinase D (SMaseD). This enzyme activity is unknown elsewhere in the animal kingdom but is shared with strains of pathogenic Corynebacteria that cause various illnesses in farm animals. The presence of the same toxic activity only in distantly related organisms poses an interesting and medically important question in molecular evolution. RESULTS: We use superpositions of recently determined structures and sequence comparisons to infer that both bacterial and spider SMaseDs originated from a common, broadly conserved domain family, the glycerophosphoryl diester phosphodiesterases. We also identify a unique sequence/structure motif present in both SMaseDs but not in the ancestral family, supporting SMaseD origin through a single divergence event in either bacteria or spiders, followed by lateral gene transfer from one lineage to the other.

Bacterial Toxins↗
PubMed2004

The complete mitochondrial genome sequence of the spider Habronattus oregonensis reveals rearranged and extremely truncated tRNAs.

We sequenced the entire mitochondrial genome of the jumping spider Habronattus oregonensis of the arachnid order Araneae (Arthropoda: Chelicerata). A number of unusual features distinguish this genome from other chelicerate and arthropod mitochondrial genomes. Most of the transfer RNA (tRNA) gene sequences are greatly reduced in size and cannot be folded into typical cloverleaf-shaped secondary structures. At least nine of the tRNA sequences lack the potential to form TPsiC arm stem pairings and instead are inferred to have TV-replacement loops. Furthermore, sequences that could encode the 3' aminoacyl acceptor stems in at least 10 tRNAs appear to be lacking, because fully paired acceptor stems are not possible and because the downstream sequences instead encode adjacent genes. Hence, these appear to be among the smallest known tRNA genes. We postulate that an RNA editing mechanism must exist to restore the 3' aminoacyl acceptor stems to allow the tRNAs to function. At least seven tRNAs are rearranged with respect to the chelicerate Limulus polyphemus, although the arrangement of the protein-coding genes is identical. Most mitochondrial protein-coding genes of H. oregonensis have ATN as initiation codons, as commonly found in arthropod mtDNAs, but cytochrome oxidase subunits 2 and 3 genes apparently use TTG as an initiation codon. Finally, many of the gene sequences overlap one another and are truncated. This 14,381-bp genome, the first mitochondrial genome of a spider yet sequenced, is one of the smallest arthropod mitochondrial genomes known. We suggest that posttranscriptional RNA editing can likely maintain function of the tRNAs, while permitting the accumulation of mutations that would otherwise be deleterious. Such mechanisms may have allowed for the minimization of the spider mitochondrial genome.

Animals↗
PubMed2006

Insects from the grazing food web favoured the evolutionary habitat shift to bright environments in araneoid spiders.

The Araneoidea comprises a diverse group of web-building spiders, and part of this diversity is believed attributable to habitat expansion to bright environments. We clarified the fitness-related advantages of living in such environments by examining prey availability and the growth rates of 10 species in three families inhabiting grassland (bright) and forest understory (dim) habitats. Spiders in the grassland habitat captured more prey, derived mainly from the grazing food web, than those in the forest-floor environment, and this difference was manifested in their growth rate. Independent contrasts indicated that increased utilization of insects from the grazing food web led to an evolutionary increase in adult body size. These results suggest that the shift to bright environments enabled araneoid spiders to evolve diverse life-history traits, including rapid growth and large size, which were not possible in dim environments.

Analysis of Variance↗
PubMed2002

Nuptial gifts of male spiders function as sensory traps.

While nuptial food gifts come in various forms in arthropods, their evolutionary origins are unclear. A previous study on insects has shown that such gifts may arise as a sensory trap that exploits a female's underlying motivation to feed. Here I present independent evidence of a sensory trap in spiders. In certain visually oriented spiders, I suggest that males initially exploit the maternal care instinct by producing a nuptial gift that closely resembles the female egg sac. Males of the spider Pisaura mirabilis cover their prey gift with a silk layer, transforming it into a white round object. In a laboratory experiment I tested whether the colour of the gift affected the rate that females accepted males displaying their gifts. I found that the brighter and the more alike the nuptial gift to a female's egg sac, the faster the female responded by grabbing the gift. My results support the hypothesis that the nuptial gift in P. mirabilis works as a sensory trap.

Animals↗
PubMed2000

Phylogeography of the jumping spider Habronattus pugillis (araneae: salticidae): recent vicariance of sky island populations?

In island systems with diverging populations, the history of island formation and genealogical estimates of divergence dates can be mutually informative. In the "sky islands" of southeastern Arizona, climate-induced contraction of woodlands appears to have fragmented populations of woodland-dwelling species onto disjunct mountain ranges. Montane populations of the jumping spider, Habronattus pugillis, display striking amounts of phenotypic divergence among ranges. Paleoclimatic estimates date woodland fragmentation at approximately 10,000 years ago, suggesting that phenotypic divergence has been extraordinarily rapid in these spiders. This phylogeographic study of populations of H. pugillis attempts to clarify the species' history of isolation and divergence and to address the suitability of available paleoclimatic data for dating divergences among populations of the region's woodland-dwelling organisms. Mitochondrial sequence data of spiders from 13 mountain ranges was used to reconstruct genealogical relationships. Gene trees show that small mountain ranges tend to have populations whose sequences form monophyletic groups, whereas larger ranges do not. Paraphyly among genes from larger ranges could result from either recent migration or incomplete lineage sorting. I use phylogenetic and geographic information to test these alternatives, and conclude that incomplete lineage sorting best explains the observed paraphyly. Gene trees are concordant with some of the predictions of vegetation history generated by examination of topography. Dates estimated for divergence of populations vary from 30,000 years to more than 2 million years ago, suggesting multiple vicariance events that are older than would be inferred from paleoclimatic studies. These findings illustrate that use of any single paleontological dataset to calibrate molecular clocks can potentially greatly underestimate actual divergence times.

Animals↗
PubMed2004

Dendritic excitability and localization of GABA-mediated inhibition in spider mechanoreceptor neurons.

GABAergic inhibition of mechanosensory afferent axon terminals is a widespread phenomenon in vertebrates and invertebrates. Spider mechanoreceptor neurons receive efferent innervation on their peripherally located axons, somata and sensory dendrites, and the dendrites have recently been shown to be excitable. Excitability of the spider sensory neurons is inhibited by muscimol and GABA, agonists of ionotropic GABA receptors. Here we asked where in the neurons this inhibition occurs. We found no evidence for inhibition of action potentials in the sensory dendrites, but axonal action potentials were rapidly suppressed by both agonists. Earlier work showed that metabotropic GABA(B) receptors are located on the dendrites and distal somata of the spider sensory neurons, where they modulate voltage-activated conductances and may provide slower, prolonged inhibition. Therefore, GABA released from single peripheral efferents may activate both ionotropic and metabotropic receptor types, providing rapid suppression of axonal activity followed by slower inhibition that eventually prevents action potential initiation in the distal dendrites.

Action Potentials↗
PubMed2006

Evolution of spider silks: conservation and diversification of the C-terminus.

Analysis of DNA sequences coding for the C-terminus of spider silk proteins from a range of spiders suggests that many silk C-termini share a common origin, and that their physical properties have been highly conserved over several hundred million years. These physical properties are compatible with roles in protein synthesis, silk function and in recruiting accessory proteins. Phylogenetic relationships among different silk genes suggest that any recombination has been insufficient to homogenize the different types of silk gene, which appear to have evolved independently of one another. The types of nucleotide substitutions that have occurred suggest that selection may have operated differently in the various silk lineages. Amino acid sequences of flagelliform silk C-termini differ substantially from the other types of spider silk studied, but they are expected to have very similar physical properties and may perform a similar function.

Amino Acid Sequence↗
PubMed1996

Silk properties determined by gland-specific expression of a spider fibroin gene family.

Spiders produce a variety of silks that range from Lycra-like elastic fibers to Kevlar-like superfibers. A gene family from the spider Araneus diadematus was found to encode silk-forming proteins (fibroins) with different proportions of amorphous glycine-rich domains and crystal domains built from poly(alanine) and poly(glycine-alanine) repeat motifs. Spiders produce silks of different composition by gland-specific expression of this gene family, which allows for a range of mechanical properties according to the crystal-forming potential of the constituent fibroins. These principles of fiber property control may be important in the development of genetically engineered structural proteins.

Amino Acid Sequence↗
PubMed2003

Acute myocardial injury caused by Sydney funnel-web spider (Atrax robustus) envenoming.

A 67-year-old female suffered envenoming by a Sydney funnel-web spider (Atrax robustus), complicated by ST elevation and elevated troponin levels consistent with an acute myocardial injury. She was treated primarily with funnel-web spider antivenom, admission to intensive care and initial respiratory support for acute pulmonary oedema. The mechanism by which funnel-web spider envenomation caused myocardial injury is unclear but follow-up nuclear studies in the patient demonstrated that she had minimal atherosclerotic disease.

Aged↗
PubMed2001

Neurogenesis in the spider Cupiennius salei.

To uncover similarities and differences in neurogenesis in arthropod groups, we have studied the ventral neuroectoderm of the spider Cupiennius salei (Chelicerata, Aranea, Ctenidae). We found that invaginating cell groups arose sequentially, at stereotyped positions in each hemisegment and in separate waves, comparable with the generation of neuroblasts in Drosophila. However, we found no evidence for proliferating stem cells that would be comparable with the neuroblasts. Instead, the whole group of invaginating cells was directly recruited to the nervous system. The invagination process is comparable with Drosophila, with the cells attaining a bottle-shaped form with the nuclei moving inwards, while actin-rich cell processes remain initially connected to the surface of the epithelium. This general pattern is also found in another spider, Pholcus phalangioides, and appears thus to be conserved at least among the Araneae. We have identified two basic helix-loop-helix encoding genes -- CsASH1 and CsASH2 -- that share sequence similarities with proneural genes from other species. Functional analysis of the genes by double-stranded RNA interference revealed that CsASH1 was required for the formation of the invagination sites and the process of invagination itself, whereas CsASH2 seemed to be required for the differentiation of the cells into neurones. Our results suggest that the basic processes of neurogenesis, as well as proneural gene function is conserved among arthropods, apart of the lack of neuroblast-like stem cells in spiders.

Amino Acid Sequence↗
PubMed2006

Ex vivo rheology of spider silk.

We investigate the rheological properties of microliter quantities of the spinning material extracted ex vivo from the major ampullate gland of a Nephila clavipes spider using two new micro-rheometric devices. A sliding plate micro-rheometer is employed to measure the steady-state shear viscosity of approximately 1 microl samples of silk dope from individual biological specimens. The steady shear viscosity of the spinning solution is found to be highly shear-thinning, with a power-law index consistent with values expected for liquid crystalline solutions. Calculations show that the viscosity of the fluid decreases 10-fold as it flows through the narrow spinning canals of the spider. By contrast, measurements in a microcapillary extensional rheometer show that the transient extensional viscosity (i.e. the viscoelastic resistance to stretching) of the spinning fluid increases more than 100-fold during the spinning process. Quantifying the properties of native spinning solutions provides new guidance for adjusting the spinning processes of synthetic or genetically engineered silks to match those of the spider.

Animals↗
PubMed1998

Different functions of different eye types in the spider Cupiennius salei.

The Central American hunting spider Cupiennius salei Keys relies mainly on its mechanosensory systems during prey-catching and mating behaviour. The behavioural relevance of its eight eyes has not been studied before, although their optics and sensitivity suggest highly developed visual capabilities. The visual system was examined in a twofold simultaneous-choice experiment. Two targets were presented at a distance of 2 m from the animals, and their walking paths towards the targets were monitored. Spiders showed no preference when choosing between two identical targets, but when choosing between two different targets they strongly preferred a vertical bar to a sloping bar or a V-shaped target. By covering all eyes except the anterior median or posterior median eyes, it could be shown that the spiders were able to detect the targets using any of the eyes. Discrimination between different targets was only possible with the anterior median eyes uncovered, although the visual fields of the anterior median and posterior median eyes overlap completely. It seems most likely that the animals separate visual information in the periphery and therefore that the eyes have different functions. The posterior median eyes support a target-detecting mechanism and the anterior median eyes a target-discrimination mechanism.

Adaptation, Ocular↗
PubMed1999

The mechanical design of spider silks: from fibroin sequence to mechanical function.

Spiders produce a variety of silks, and the cloning of genes for silk fibroins reveals a clear link between protein sequence and structure-property relationships. The fibroins produced in the spider's major ampullate (MA) gland, which forms the dragline and web frame, contain multiple repeats of motifs that include an 8-10 residue long poly-alanine block and a 24-35 residue long glycine-rich block. When fibroins are spun into fibres, the poly-alanine blocks form (&bgr;)-sheet crystals that crosslink the fibroins into a polymer network with great stiffness, strength and toughness. As illustrated by a comparison of MA silks from Araneus diadematus and Nephila clavipes, variation in fibroin sequence and properties between spider species provides the opportunity to investigate the design of these remarkable biomaterials.

Amino Acid Sequence↗
PubMed2005

Have male and female genitalia coevolved? A phylogenetic analysis of genitalic morphology and sexual size dimorphism in web-building spiders (Araneae: Araneoidea).

Sexual size dimorphism (SSD) can strongly influence the evolution of reproductive strategies and life history. If SSD is extreme, and other characters (e.g., genitalic size) also increase with size, then functional conflicts may arise between the sexes. Spiders offer an excellent opportunity to investigate this issue because of their wide range of SSD. By using modern phylogenetic methods with 16 species of orb-weaving spiders, we provide strong evidence for the "positive genitalic divergence" model, implying that sexual genitalic dimorphism (SGD) increases as SSD increases. This pattern is supported by an evolutionary mismatch between the absolute sizes of male and female genitalia across species. Indeed, our findings reveal a dramatic reversal from male genitalia that are up to 87x larger than female genitalia in size-monomorphic species to female genitalia that are up to 2.8x larger in extremely size-dimorphic species. We infer that divergence in SGD could limit SSD both in spiders, and potentially in other taxa as well. Further, male and female body size, as well as male and female genitalia size, are decoupled evolutionarily. Finally, we show a negative scaling (hypoallometry) of male and female genitalic morphology within sexes. Evolutionary forces specific to each sex, such as larger female size (increased fecundity) or smaller male size (enhanced mate-searching ability), may be balanced by stabilizing selection on relative genitalic size.

Animals↗
PubMed2004

Analysis on the dispersal pattern of newly introduced Latrodectus hasseltii (Araneae: Theridiadae) in Japan by spider diagram.

The dispersal pattern of the widow spider Latrodectus hasseltii (Araneae: Theridiadae), in Osaka Prefecture, Japan, was analyzed from accumulated survey data of spider distribution. All confirmed infested points from 1996 to 2002 were plotted on a map, and infested points in each survey year were connected with the nearest previously confirmed points. Expansion patterns of the confirmed habitats were analyzed by year and dispersion distances were classified by using spider diagram, one of method of geographical information system spatial analysis. L. hasseltii moves by walking step by step on the ground, mainly in coastal areas during early stages of infestation, and also can be conveyed over distances by various vehicles, mainly in inland areas. These analyses show L. hasseltii does not move by ballooning.

Animals↗
PubMed1995

Startle responses of spider phobics to masked stimuli: a pilot study.

The present study tested the hypothesis that briefly flashed and backwardly masked phobic stimuli potentiate startle reflexes in phobic subjects. Spider phobic (n = 17) and normal control (n = 12) subjects were exposed to short (30 ms) and backwardly masked presentations of phobic slides (i.e., spiders) and neutral slides (i.e., flowers, mushrooms, snakes). On half the trials, eyeblink startle reflexes were elicited with auditory probes following presentation of the slides. In spite of the degraded stimulus conditions, there were some indications that phobics exhibited a startle pattern different from control subjects. More specifically, phobic subjects tended to react with larger startles during the second block of spider trials than control subjects. No such group differences were found for the neutral trials. As the eyeblink startle reflex is closely linked to the thalamo-amygdala pathway, the present findings provide some preliminary support for the idea that the preattentive processing of phobic cues is located at the subcortical level.

Adult↗