The Experts below are selected from a list of 2568036 Experts worldwide ranked by ideXlab platform
Andis Graudins - One of the best experts on this subject based on the ideXlab platform.
-
antivenom treatment in arachnidism
Clinical Toxicology, 2003Co-Authors: Geoffrey K Isbister, Andis Graudins, David A WarrellAbstract:Envenomation by arachnids causes significant medical illness worldwide. Scorpion sting is the most important arachnid envenomation causing adult morbidity and pediatric mortality. Important groups of spiders include the widow spiders (Latrodectus spp.), the recluse spiders (Loxosceles spp.), and two spiders confined to single countries: the Australian funnel web spider (Atrax and Hadronyche spp.) and the armed spider (Phoneutria spp.) from Brazil. There are four widow spider antivenoms available, including the Australian redback spider antivenom and the American black widow antivenom. Despite good in vitro animal work demonstrating effective neutralization with these antivenoms, and cross-reactivity between many species, there continues to be a reluctance to use them in some countries. They are both associated with a relatively low rate of allergic reactions. Redback antivenom is routinely used by the intramuscular route, which may not be as effective as intravenous use based on clinical experience and animal studies. Antivenoms are available for Loxosceles spp., but there is little evidence to support their effectiveness, particularly against local effects. The Australian funnel web spider causes severe neurotoxic envenomation, and antivenom appears to be effective in reported cases. An antivenom exists for the Brazilian armed spider, but is used in only a minority of cases. Many scorpion antivenoms exist worldwide, but there remains significant controversy regarding their efficacy. Animal and human venom level studies demonstrate neutralization of circulating venom in systemic envenomation. Clinical experience in countries where antivenom has been introduced suggests it has reduced pediatric mortality. However, three controlled trials demonstrated that antivenom was not effective, but these included few severe cases. Until controlled trials of antivenom in systemically envenomated patients are undertaken, antivenom use appears justified in severe envenomation. Although envenomation from arthropods is common, no antivenoms exist for these, excepting Lonomia caterpillars in South America, and Ixodes paralysis ticks in Australia.
-
spiders of medical importance in the asia pacific atracotoxin latrotoxin and related spider neurotoxins
Clinical and Experimental Pharmacology and Physiology, 2002Co-Authors: Graham M Nicholson, Andis GraudinsAbstract:1. The spiders of medical importance in the Asia-Pacific region include widow (family Theridiidae) and Australian funnel-web spiders (subfamily Atracinae). In addition, cupboard (family Theridiidae) and Australian mouse spiders (family Actinopodidae) may contain neurotoxins responsible for serious systemic envenomation. Fortunately, there appears to be extensive cross-reactivity of species-specific widow spider antivenom within the family Theridiidae. Moreover, Sydney funnel-web antivenom has been shown to be effective in the treatment of mouse spider envenomation. 2. alpha-Latrotoxin (alpha-LTx) appears to be the main neurotoxin responsible for the envenomation syndrome known as "latrodectism" following bites from widow spiders. This 120 kDa protein binds to distinct receptors (latrophilin 1 and neurexins) to induce neurotransmitter vesicle exocytosis via both Ca2+-dependent and -independent mechanisms, resulting in vesicle depletion. This appears to involve disruption to a process that normally inhibits vesicle fusion in the absence of Ca2+. Precise elucidation of the mechanism of action of alpha-LTx will lead to a major advancement in our understanding of vesicle exocytosis. 3. delta-Atracotoxins (delta-ACTX) are responsible for the primate-specific envenomation syndrome seen following funnel-web spider envenomation. These peptides induce spontaneous repetitive firing and prolongation of action potentials in excitable cells. This results from a hyperpolarizing shift of the voltage-dependence of activation and a slowing of voltage-gated Na+ channel inactivation. This action is due to voltage-dependent binding to neurotoxin receptor site-3 on insect and mammalian voltage-gated Na+ channels in a manner similar, but not identical, to scorpion alpha-toxins and sea anemone toxins. delta-Atracotoxins provide us with highly specific tools to study Na+ channel structure and function 4. omega- and Janus-faced ACTX, from funnel-web spider venom, are novel neurotoxins that show selective toxicity to insects. In particular omega-ACTX define a new insecticide target due to a specific action to block insect voltage-gated Ca2+ channels. Both these ACTX show promise for the development of baculoviral recombinant biopesticides expressing these toxins for the control of insecticide-resistant agricultural pests. In addition, they should provide valuable tools for the pharmacological and structural characterization of insecticide targets.
-
Cross-reactivity of Sydney funnel-web spider antivenom: neutralization of the in vitro toxicity of other Australian funnel-web (Atrax and Hadronyche) spider venoms
Toxicon : official journal of the International Society on Toxinology, 2002Co-Authors: Andis Graudins, Paul Francis Alewood, David Wilson, Kevin W. BroadyAbstract:Australian funnel-web spiders are recognized as one of the most venomous spiders to humans world-wide. Funnel-web spider antivenom (FWS AV) reverses clinical effects of envenomation from the bite of Atrax robustus and a small number of related Hadronyche species. This study assessed the in vitro efficacy of FWS AV in neutralization of the effects of funnel-web spider venoms, collected from various locations along the eastern seaboard of Australia, in an isolated chick biventer cervicis nerve–muscle preparation. Venoms were separated by SDS-PAGE electrophoresis to compare protein composition and transblotted for Western blotting and incubation with FWS AV. SDS-PAGE of venoms revealed similar low and high molecular weight protein bands. Western blotting with FWS AV showed similar antivenom binding with protein bands in all the venoms tested. Male funnel-web spider venoms (7/7) and female venoms (5/10) produced muscle contracture and fasciculation when applied to the nerve–muscle preparation. Venom effects were reversed by subsequent application of FWS AV or prevented by pretreatment of the preparation with antivenom. FWS AV appears to reverse the in vitro toxicity of a number of funnel-web spider venoms from the eastern seaboard of Australia. FWS AV should be effective in the treatment of envenomation from most, if not all, species of Australian funnel-web spiders.
Ingi Agnarsson - One of the best experts on this subject based on the ideXlab platform.
-
spider phylogenomics untangling the spider tree of life
PeerJ, 2016Co-Authors: Nicole L Garrison, Chris A Hamilton, Marshal Hedin, Ingi Agnarsson, Jonathan A Coddington, Juanita Rodriguez, Charles E Griswold, Kevin M Kocot, Joel M Ledford, Jason E BondAbstract:Spiders (Order Araneae) are massively abundant generalist arthropod predators that are found in nearly every ecosystem on the planet and have persisted for over 380 million years. Spiders have long served as evolutionary models for studying complex mating and web spinning behaviors, key innovation and adaptive radiation hypotheses, and have been inspiration for important theories like sexual selection by female choice. Unfortunately, past major attempts to reconstruct spider phylogeny typically employing the "usual suspect" genes have been unable to produce a well-supported phylogenetic framework for the entire order. To further resolve spider evolutionary relationships we have assembled a transcriptome-based data set comprising 70 ingroup spider taxa. Using maximum likelihood and shortcut coalescence-based approaches, we analyze eight data sets, the largest of which contains 3,398 gene regions and 696,652 amino acid sites forming the largest phylogenomic analysis of spider relationships produced to date. Contrary to long held beliefs that the orb web is the crowning achievement of spider evolution, ancestral state reconstructions of web type support a phylogenetically ancient origin of the orb web, and diversification analyses show that the mostly ground-dwelling, web-less RTA clade diversified faster than orb weavers. Consistent with molecular dating estimates we report herein, this may reflect a major increase in biomass of non-flying insects during the Cretaceous Terrestrial Revolution 125-90 million years ago favoring diversification of spiders that feed on cursorial rather than flying prey. Our results also have major implications for our understanding of spider systematics. Phylogenomic analyses corroborate several well-accepted high level groupings: Opisthothele, Mygalomorphae, Atypoidina, Avicularoidea, Theraphosoidina, Araneomorphae, Entelegynae, Araneoidea, the RTA clade, Dionycha and the Lycosoidea. Alternatively, our results challenge the monophyly of Eresoidea, Orbiculariae, and Deinopoidea. The composition of the major paleocribellate and neocribellate clades, the basal divisions of Araneomorphae, appear to be falsified. Traditional Haplogynae is in need of revision, as our findings appear to support the newly conceived concept of Synspermiata. The sister pairing of filistatids with hypochilids implies that some peculiar features of each family may in fact be synapomorphic for the pair. Leptonetids now are seen as a possible sister group to the Entelegynae, illustrating possible intermediates in the evolution of the more complex entelegyne genitalic condition, spinning organs and respiratory organs.
-
phylogenomics resolves a spider backbone phylogeny and rejects a prevailing paradigm for orb web evolution
Current Biology, 2014Co-Authors: Jason E Bond, Nicole L Garrison, Chris A Hamilton, Rebecca L Godwin, Marshal Hedin, Ingi AgnarssonAbstract:Summary Spiders represent an ancient predatory lineage known for their extraordinary biomaterials, including venoms and silks. These adaptations make spiders key arthropod predators in most terrestrial ecosystems. Despite ecological, biomedical, and biomaterial importance, relationships among major spider lineages remain unresolved or poorly supported [1]. Current working hypotheses for a spider ‘‘backbone’’ phylogeny are largely based on morphological evidence, as most molecular markers currently employed are generally inadequate for resolving deeper-level relationships. We present here a phylogenomic analysis of spiders including taxa representing all major spider lineages. Our robust phylogenetic hypothesis recovers some fundamental and uncontroversial spider clades, but rejects the prevailing paradigm of a monophyletic Orbiculariae, the most diverse lineage, containing orb-weaving spiders. Based on our results, the orb web either evolved much earlier than previously hypothesized and is ancestral for a majority of spiders or else it has multiple independent origins, as hypothesized by precladistic authors. Cribellate deinopoid orb weavers that use mechanically adhesive silk are more closely related to a diverse clade of mostly webless spiders than to the araneoid orb-weaving spiders that use adhesive droplet silks. The fundamental shift in our understanding of spider phylogeny proposed here has broad implications for interpreting the evolution of spiders, their remarkable biomaterials, and a key extended phenotype—the spider web.
-
the form and function of spider orb webs evolution from silk to ecosystems
Advances in Insect Physiology, 2011Co-Authors: Todd A Blackledge, Matjaž Kuntner, Ingi AgnarssonAbstract:Spiders are the preeminent silk craftsmen among arthropods and are best known for producing aerial orb webs that snare flying insects. Orb web spiders are ubiquitous predators in terrestrial ecosystems and are popular models for behavioural and ecological research, in part due to the ease of characterizing the shapes of orb webs. Orb webs are composite structures built from multiple types of silks, each with its own unique molecular structure and mechanical function, such that orb webs also link together evolutionary research from the genes coding for silk proteins to whole web function in the environment. Yet, orb webs are only intermediate structures in the evolutionary diversification of silk use among spiders, acting as stepping stones facilitating the origin of new web types and increased spider diversification. Here, we review the current research on the form and function of spider orb webs. We provide a comprehensive introduction to all aspects of orb web biology, suitable for any new investigation into orb web biology. While other reviews exist individually for webs, silk, and spider evolution, we hope that the synthetic nature of this review will facilitate a more integrated approach by future investigators. Finally, we explore in more detail some of the most dynamic areas of orb web biology to suggest promising venues for the next decade of research on these fascinating creatures and their silken snares. In particular, we discuss how spider webs might drive speciation, the dramatic growth in our understanding of the molecular ecology of spider silk, and the importance of a greater role for spider biology per se in silk biomimicry.
-
reconstructing web evolution and spider diversification in the molecular era
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Todd A Blackledge, Cheryl Y. Hayashi, Nikolaj Scharff, Jonathan A Coddington, Tamas Szuts, John W Wenzel, Ingi AgnarssonAbstract:The evolutionary diversification of spiders is attributed to spectacular innovations in silk. Spiders are unique in synthesizing many different kinds of silk, and using silk for a variety of ecological functions throughout their lives, particularly to make prey-catching webs. Here, we construct a broad higher-level phylogeny of spiders combining molecular data with traditional morphological and behavioral characters. We use this phylogeny to test the hypothesis that the spider orb web evolved only once. We then examine spider diversification in relation to different web architectures and silk use. We find strong support for a single origin of orb webs, implying a major shift in the spinning of capture silk and repeated loss or transformation of orb webs. We show that abandonment of costly cribellate capture silk correlates with the 2 major diversification events in spiders (1). Replacement of cribellate silk by aqueous silk glue may explain the greater diversity of modern orb-weaving spiders (Araneoidea) compared with cribellate orb-weaving spiders (Deinopoidea) (2). Within the “RTA clade,” which is the sister group to orb-weaving spiders and contains half of all spider diversity, >90% of species richness is associated with repeated loss of cribellate silk and abandonment of prey capture webs. Accompanying cribellum loss in both groups is a release from substrate-constrained webs, whether by aerially suspended webs, or by abandoning webs altogether. These behavioral shifts in silk and web production by spiders thus likely played a key role in the dramatic evolutionary success and ecological dominance of spiders as predators of insects.
Todd A Blackledge - One of the best experts on this subject based on the ideXlab platform.
-
the form and function of spider orb webs evolution from silk to ecosystems
Advances in Insect Physiology, 2011Co-Authors: Todd A Blackledge, Matjaž Kuntner, Ingi AgnarssonAbstract:Spiders are the preeminent silk craftsmen among arthropods and are best known for producing aerial orb webs that snare flying insects. Orb web spiders are ubiquitous predators in terrestrial ecosystems and are popular models for behavioural and ecological research, in part due to the ease of characterizing the shapes of orb webs. Orb webs are composite structures built from multiple types of silks, each with its own unique molecular structure and mechanical function, such that orb webs also link together evolutionary research from the genes coding for silk proteins to whole web function in the environment. Yet, orb webs are only intermediate structures in the evolutionary diversification of silk use among spiders, acting as stepping stones facilitating the origin of new web types and increased spider diversification. Here, we review the current research on the form and function of spider orb webs. We provide a comprehensive introduction to all aspects of orb web biology, suitable for any new investigation into orb web biology. While other reviews exist individually for webs, silk, and spider evolution, we hope that the synthetic nature of this review will facilitate a more integrated approach by future investigators. Finally, we explore in more detail some of the most dynamic areas of orb web biology to suggest promising venues for the next decade of research on these fascinating creatures and their silken snares. In particular, we discuss how spider webs might drive speciation, the dramatic growth in our understanding of the molecular ecology of spider silk, and the importance of a greater role for spider biology per se in silk biomimicry.
-
reconstructing web evolution and spider diversification in the molecular era
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Todd A Blackledge, Cheryl Y. Hayashi, Nikolaj Scharff, Jonathan A Coddington, Tamas Szuts, John W Wenzel, Ingi AgnarssonAbstract:The evolutionary diversification of spiders is attributed to spectacular innovations in silk. Spiders are unique in synthesizing many different kinds of silk, and using silk for a variety of ecological functions throughout their lives, particularly to make prey-catching webs. Here, we construct a broad higher-level phylogeny of spiders combining molecular data with traditional morphological and behavioral characters. We use this phylogeny to test the hypothesis that the spider orb web evolved only once. We then examine spider diversification in relation to different web architectures and silk use. We find strong support for a single origin of orb webs, implying a major shift in the spinning of capture silk and repeated loss or transformation of orb webs. We show that abandonment of costly cribellate capture silk correlates with the 2 major diversification events in spiders (1). Replacement of cribellate silk by aqueous silk glue may explain the greater diversity of modern orb-weaving spiders (Araneoidea) compared with cribellate orb-weaving spiders (Deinopoidea) (2). Within the “RTA clade,” which is the sister group to orb-weaving spiders and contains half of all spider diversity, >90% of species richness is associated with repeated loss of cribellate silk and abandonment of prey capture webs. Accompanying cribellum loss in both groups is a release from substrate-constrained webs, whether by aerially suspended webs, or by abandoning webs altogether. These behavioral shifts in silk and web production by spiders thus likely played a key role in the dramatic evolutionary success and ecological dominance of spiders as predators of insects.
-
fine dining or fortress functional shifts in spider web architecture by the western black widow latrodectus hesperus
Animal Behaviour, 2008Co-Authors: Jacquelyn M Zevenbergen, Nicole K Schneider, Todd A BlackledgeAbstract:Spiders alter web architecture in response to many environmental factors. Yet, the functional implications of this behavioural plasticity are poorly understood, especially for spiders that spin long-lasting webs such as cobwebs. The western black widow spins a three-dimensional web that captures terrestrial prey and can persist for many days. However, the shape of the cobweb depends upon changes in the spider's body condition. Starved spiders invest more silk in sticky gumfooted threads, whereas sated spiders invest more silk in supporting threads. We tested the hypothesis that the increased investment in sticky gumfooted threads by starved spiders functions to improve the prey capture of their webs. Regardless of intrinsic foraging motivation, both fed and starved spiders captured more prey, more quickly and more efficiently, when hunting on a web that was spun by a starved spider. Our study shows that cobweb spiders actively manipulate web-spinning behaviours in ways that alter the functions of their webs and that even spiders spinning relatively long-lasting webs may use behavioural plasticity to respond to changing selective pressures in their environment.
Astrid M Heiling - One of the best experts on this subject based on the ideXlab platform.
-
the role of experience in web building spiders araneidae
Animal Cognition, 1999Co-Authors: Astrid M Heiling, Marie E HerbersteinAbstract:A typical feature of vertical orb-webs is the ‘top/bottom’ asymmetry, where the lower web region is larger than the upper web region. This asymmetry may improve prey capture success, because, sitting in the hub of the web, a spider can reach prey entangled below the hub faster than prey entangled in the area above the hub. While web asymmetry is known to vary intraspecifically, we tested if this variation also exists at the individual level and whether it is the result of experience, using two orb-web spider species, Argiope keyserlingi and Larinioides sclopetarius. The results reveal that experienced web-building spiders constructed more asymmetric webs than conspecifics deprived of any prior building experience over a period of several months. Experienced individuals invested more silk material into the web region below the hub, which covered a larger area. Moreover, web asymmetry was also influenced by previous prey capture experiences, as spiders increased the lower region of the web if it intercepted the most prey over a period of 6 days. Consequently, spiders may be able to use long-term web-building experience as well as short-term prey capture experience to build better traps. In contrast to previous views of spiders, experience can contribute to intraspecific as well as to individual variations in web design.
-
why do nocturnal orb web spiders araneidae search for light
Behavioral Ecology and Sociobiology, 1999Co-Authors: Astrid M HeilingAbstract:The nocturnal orb-web spider Larinioides sclopetarius lives near water and frequently builds webs on bridges. In Vienna, Austria, this species is particularly abundant along the artificially lit handrails of a footbridge. Fewer individuals placed their webs on structurally identical but unlit handrails of the same footbridge. A census of the potential prey available to the spiders and the actual prey captured in the webs revealed that insect activity was significantly greater and consequently webs captured significantly more prey in the lit habitat compared to the unlit habitat. A laboratory experiment showed that adult female spiders actively choose artificially lit sites for web construction. Furthermore, this behaviour appears to be genetically predetermined rather than learned, as laboratory-reared individuals which had previously never foraged in artificial light exhibited the same preference. This orb-web spider seems to have evolved a foraging behaviour that exploits the attraction of insects to artificial lights.
-
the web of nuctenea sclopetaria araneae araneidae relationship between body size and web design
Journal of Arachnology, 1998Co-Authors: Astrid M Heiling, Marie E HerbersteinAbstract:The relationship between body size and web design was studied for the nocturnal orb- weaving spider Nuctenea sclopetaria .Body measurements (carapace width, leg length, body length and wet weight) taken from 27 adult female and 22 juvenile spiders were related to web dimensions (capture area, number of radii, capture thread length, mesh height) each spider constructed . Carapace width was found to be the most reliable size measure for predicting web dimensions for adult and juvenile spiders . The study also found that the webs showed a distinct asymmetry due to the enlargement of the lower web half and the extent of this asymmetry increased with carapace width . Furthermore, mesh height increased with distance from the hub . The possible effects of web asymmetry on the prey capture success of spiders are discussed .
Xinxing He - One of the best experts on this subject based on the ideXlab platform.
-
functional redundancy dampens the trophic cascade effect of a web building spider in a tropical forest floor
Soil Biology & Biochemistry, 2016Co-Authors: Jocelyn E Behm, Xinxing He, Shenglei Fu, Jing Hu, Jin Chen, Douglas SchaeferAbstract:Abstract The trophic cascade effect of predators on ecosystem functioning is generally believed to be less frequent and weaker in detritus-based than primary producer-based food webs, in part because of functional redundancy among soil fauna. Despite this view, no empirical studies have explicitly examined roles of different soil fauna within trophic levels in mediating cascading effects of predators in detritus food webs. Here we manipulated the density of a dominant funnel-web building spider Macrothele yunnanica in permanent plots (1 m 2 ) for one year. Three spider treatments were applied: 0 spiders, 6 spiders (natural density) and 10 spiders (high density). We found that although changes in spider densities caused large shifts in litter-dwelling Collembola community composition on average, modifying spider densities did not generate a trophic cascade effect and alter litter decomposition in litter bags with coarse mesh (2 mm). Our data supports the hypothesis that functional redundancy among Collembola species may weaken the strength of spider-initiated cascading effects. Consequently, changes in Collembola diversity occupying the same trophic level may not significantly alter ecosystem function in tropical forest-floor ecosystems.
-
trophic cascade of a web building spider decreases litter decomposition in a tropical forest floor
European Journal of Soil Biology, 2014Co-Authors: Jin Chen, Xinxing He, Jing HuAbstract:Abstract Trophic cascade effects on detritus-based food webs of forest floor have the potential to alter ecosystem functioning, but due to the complexity of detrital food web no general pattern of cascading effects has emerged. The goal of this study was to evaluate trophic cascade effects of a dominant funnel-web building spider on leaf-litter decomposition rate and microbial biomass in a tropical forest floor. We manipulated the density of a dominant funnel-web building spider Macrothele yunnanica in permanent plots (1 m 2 ) for one year. Three spider treatments were applied: 0 spider, 6 spiders (natural density) and 10 spiders (high density). We found that the high density of M. yunnanica led to significant negative cascading effects on litter decomposition rate, which is probably due to decreased density of one dominant collembolan, Entomobrya , in the litter layer. We detected no cascading effects from the natural density of M. yunnanica , and changes in spider densities had no cascading effects on microbial biomass. Modifying spider densities can generate a trophic cascade effect and alter leaf litter decomposition, with a potential to influence ecosystem function in tropical forest floors. This study suggests that trophic interactions in detritus-based food webs should be considered to better understand soil organic matter dynamics in tropical forests.