Spider Research Articles

Molecular phylogeny of the orb-weaving spider genus Leucauge and the intergeneric relationships of Leucauginae (Araneae, Tetragnathidae)

The tetragnathid genus Leucauge includes some of the most common orb-weaving spiders in the tropics. Although some species in this genus have attained relevance as model systems for several aspects of spider biology, our understanding of the generic diversity and evolutionary relationships among the species is poor. In this study we present the first attempt to determine the phylogenetic structure within Leucauge and the relationship of this genus with other genera of Leucauginae. This is based on DNA sequences from the five loci commonly used and Histone H4, used for the first time in spider phylogenetics. We also assess the informativeness of the standard markers and test for base composition biases in the dataset. Our results suggest that Leucauge is not monophyletic since species of the genera Opas, Opadometa, Mecynometa and Alcimosphenus are included within the current circumscription of the genus. Based on a phylogenetic re-circumscription of the genus to fulfil the requirement for monophyly of taxa, Leucauge White, 1841 is deemed to be a senior synonym of the genera Opas Pickard-Cambridge, 1896 revalidated synonymy, Mecynometa Simon, 1894 revalidated synonymy, Opadometa Archer, 1951 new synonymy and Alcimosphenus Simon, 1895 new synonymy. We identify groups of taxa critical for resolving relationships within Leucauginae and describe the limitations of the standard loci for accomplishing these resolutions.

Abundance changes in orb-weaver spider communities at the edge of the Argiope bruennichi expansion range.

Expanding range is an inherent feature of any species and may be caused by climate change, destruction or other change of habitat, or lack of natural enemies. In a new habitat the species may be neutral, or as predator it can displace related species through competition. A strong expansion to northern Europe was observed in the thermophilous spider species Argiope bruennichi. The species doubled its range in Poland during the 1990s and its impact on native species was not investigated so far. In this article, the results of studies about A. bruennichi number (density) and its contribution in orb-weaver spider communities are analysed. We also try to determine the impact of newly occurring species on the local araneofauna.

An investigation of diversity and bioecology of araneofauna of Pathiramanal Island in Vembanad Lake, a Ramsar site, Kerala, India

A preliminary checklist of araneofauna of Pathiramanal Island is provided. A total of 147 species belonging to 26 families under 92 genera are documented. Tylorida ventralis (Thorell 1877) is considered to be the dominant species, and orb weavers are seen as the dominant guild. Araneidae, Salticidae, Theridiidae, Tetragnathidae and Thomisidae are five dominant families. The Shannon diversity, Simpson’s (1-D) diversity, evenness and Chao1 indices have been calculated. Seven species new to science such as Indopadilla insularis, Epeus triangulopalpis, Marengo sachintendulkar, Indomarengo chavarapater, Icius vikrambatrai, Piranthus planolancis (Salticidae) and Wolongia papafrancisi (Tetragnathidae) are documented as well as three genera and four species are added to the Indian spider taxonomy. The males of Meotipa picturara, Curubis tetrica and Pscellonus planus are described for the first time. Eight species are synonymized and redescribed. Mating plug formation in Argyrodes flavescens is reported for the first time. It is noted that spider species from Pathiramanl Island bear affinities with Oriental and Palearctic regions.

Redescription of Tetragnatha guatemalensis, T. laboriosa and T. jaculator, with new synonymies of genus Tetragnatha (Araneae: Tetragnathidae) in the Neotropical Region

ABSTRACT We redescribe three species of the long-jawed orb-weaving spiders of the cosmopolitan genus Tetragnatha based on specimens from the Neotropical Region, all recorded from South America for the first time. Tetragnatha guatemalensis O. Pickard-Cambridge, 1889 is newly recorded from Brazil (Rondônia, Tocantins, Mato Grosso do Sul, São Paulo, Santa Catarina and Rio Grande do Sul states). Tetragnatha laboriosa Hentz, 1850 is newly recorded from Cuba (Santiago de Cuba province), Dominican Republic (Bahoruco province), Brazil (Sergipe, São Paulo and Rio Grande do Sul states), Chile (Valparaíso province), Paraguay (Misiones province) and Argentina (Corrientes, Neuquén, Río Negro and Santa Cruz provinces). Tetragnatha jaculator Tullgren, 1910 is newly recorded from Cuba (Holguín province), some states of Brazil (Pará, Maranhão, Paraíba, Pernambuco, Sergipe, Mato Grosso do Sul, São Paulo, Paraná and Santa Catarina) and Chile (Malleco commune). Finally, we proposed six new synonymies for these species.

Long-read transcriptomic analysis of orb-weaving spider Araneus ventricosus indicates transcriptional diversity of spidroins

Spider silk, which is composed of diverse silk proteins (spidroin), is a kind of natural high-mass biomaterial with great potential. However, due to the complexity of both the structure and the composition of the spidroins in natural spider silk, application of this valuable biomass is still limited to date. There are diverse kinds of spider silk in the orb-weaving spider with different mechanical and structural characteristics. In order to systematically illustrate the landscape of all the different spidrons, here we chose Araneus ventricosus, an orb-weaving spider with superior silk mechanical features and genome information, to generate a long-read whole body transcriptome. We deciphered the repeat arrangements of each kind of spidroin, based on which we found that there are substantially transcriptional diversity of each spidroin gene. Some repeat motifs are not documented before. Specifically, we discovered novel full-lengh MaSp transcript as well as a relatively small full-length AcSp isoforms, which are potential promising materials for bioengineering of recombinant spidroin. Our study provided a batch of new spidron resources with detail sequential information. The finding of transcriptional diversity may provide cues in understanding of within-species variation of the mechanical properties of the natural spider silk and further molecular designing of recombinant spidroin.

Analysis the water in aggregate glue droplets of spider orb web by TOF‐SIMS

Orb‐weaver spiders of the family Araneidae produce a viscous glue from aggregate glands. Spiders effectively capture prey by coating the viscous glue onto the spiral lines. The viscous glue has an unusual property. The main components are glycoproteins, salts (low molecular mass compounds [LMMCs] and inorganic salt), and water. The interaction of water and glycoproteins relies on the presence of salts. Here, we used a freeze method to analyze the behavior of water of the viscous glue using time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). We found that the matrix effect of glycoprotein may cause ion suppression of water in aggregate glue droplets. Moreover, the changes in element distribution before and after the viscous glue adheres to the object suggest that after losing salts, water not only ceases to interact with glycoproteins but also oozes with the salts.

An Afrotropic element at the north-western periphery of the Oriental Region: Pseudomicrommata mokranica sp. nov. (Araneae: Sparassidae)

The surprising discovery of a new species of grass huntsman spider, Pseudomicrommata mokranica sp. nov. (♂♀), belonging to “the African clade”, is reported and described from south-eastern Iran, more than 4000 km away from the nearest recorded locality of the genus in Kenya. Similar vicariant occurrences of other sparassid taxa in Africa and Asia are discussed.

Mechanical and structural properties of major ampullate silk from spiders fed carbon nanomaterials.

The dragline silk of spiders is of particular interest to science due to its unique properties that make it an exceptional biomaterial that has both high tensile strength and elasticity. To improve these natural fibers, researchers have begun to try infusing metals and carbon nanomaterials to improve mechanical properties of spider silk. The objective of this study was to incorporate carbon nanomaterials into the silk of an orb-weaving spider, Nephila pilipes, by feeding them solutions containing graphene and carbon nanotubes. Spiders were collected from the field and in the lab were fed solutions by pipette containing either graphene sheets or nanotubes. Major ampullate silk was collected and a tensile tester was used to determine mechanical properties for pre- and post-treatment samples. Raman spectroscopy was then used to test for the presence of nanomaterials in silk samples. There was no apparent incorporation of carbon nanomaterials in the silk fibers that could be detected with Raman spectroscopy and there were no significant improvements in mechanical properties. This study represents an example for the importance of attempting to replicate previously published research. Researchers should be encouraged to continue to do these types of investigations in order to build a strong consensus and solid foundation for how to go forward with these new methods for creating novel biomaterials.

The prey’s catching problem in an elastically supported spider orb-web

Spiders use their orb-web not only to capture prey, but also as a sensor to detect the position of the area where it has impacted. The web, serving as a waveguide, transmits to its eight legs the vibratory information so that the spider can orient itself towards the prey, performing a task similar to solving an inverse problem. Although the response of spiders to vibrations has been studied for over 100 years, the understanding of the dynamic response of the web and its ability to serve as a sensor remains largely incomplete. Some recent work has made significant progress in this area, in particular in the formulation of the catching problem as an inverse problem (Kawano and Morassi [1,2]), using a continuous membrane model for the orb-web (Morassi et al. [3]). Here, we continue this line of research by relaxing the condition of null displacement at the boundary of the web (rigid support) that was considered in previous studies, thus approaching the reality of a not necessarily rigid substrate (e.g., leaves) to which spiders anchor their web. The creation of a reconstruction algorithm for identifying the load support provides an answer to the inverse problem. Additionally, the adoption of the support stiffness as a fundamental parameter of the study allows the analysis of its influence on the quality of the identification.

Hub thread removal behaviour in the orb weaver Leucauge mariana (Araneae: Tetragnathidae)

Many orb-weaving spiders break the central lines of the hub at the end of web construction. Nevertheless, very little is known of how spiders break these lines and whether this behaviour differs among taxa. Here, we describe details of how Leucauge mariana (Taczanowski, 1981) breaks the central lines of the hub. Breaking hub lines varies among individuals of a single species, and may differ between species.

Spider webs inspiring soft robotics.

In soft robotics, bio-inspiration ranges from hard- to software. Orb web spiders provide excellent examples for both. Adapted sensors on their legs may use morphological computing to fine-tune feedback loops that supervise the handling and accurate placement of silk threads. The spider's webs embody the decision rules of a complex behaviour that relies on navigation and piloting laid down in silk by behaviour charting inherited rules. Analytical studies of real spiders allow the modelling of path-finding construction rules optimized in evolutionary algorithms. We propose that deconstructing spiders and unravelling webs may lead to adaptable robots able to invent and construct complex novel structures using relatively simple rules of thumb.

Sit-and-wait forager or aggressive spider predator: Araneophagic cases of orb-weaving spiders by crab spiders of the genus Thomisus (Araneae: Thomisidae)

Sit-and-wait forager or aggressive spider predator: Araneophagic cases of orb-weaving spiders by crab spiders of the genus Thomisus (Araneae: Thomisidae)

A new record of the nocturnal orb-weaving spider Poltys illepidus (Araneae: Araneidae) from northern Thailand

The orb-weaving spider Poltys illepidus Koch 1843 is recorded from northern Thailand for the first time. The distribution of the species in Southeast Asia is extended northwest. The morphotype is characterized by an unusual small accessory protuberance on the carapace which is described and illustrated as a median anterior process without apparent function. Keywords: arachnid, biogeography, distribution, morphotype, Southeast Asia

No edge effect on quantity of prey captured in the forest-dwelling tetragnathid orb spider Metellina mengei

Abstract Among the most damaging anthropogenic effects for ecosystems is habitat fragmentation. One of its consequences is the creation of edges, which results in more exposed habitats that have different ecological and behavioural effects on the different species that live there. However, the nature and magnitude of these effects remain unknown for most of the animals and plants inhabiting these edge habitats. This study intends to determine if quantity of prey capture by a woodland population of the orb spider Metellina mengei is subjected to edge effects. By observing the prey capture of this species at edge and interior locations of a woodland, we found no significant effects of edge on the number of prey captured or the average prey length. Instead, we found that inclination of the web, but not web area or other measured web parameters, had a significant effect on prey capture. Therefore, this species of spider may be minimally affected by its location within the woodland and more affected by its surrounding microhabitat, which raises the possibility that non-specialised invertebrate predators could be less impacted by fragmentation than generally recognised.

The spider's web and the parrot's eloquence. The intriguing visual plots, frescoed by Donato Decumbertino in Gambatesa

The spider's web and the parrot's eloquence. The intriguing visual plots, frescoed by Donato Decumbertino in Gambatesa

Free-standing spider silk webs of the thomisid Saccodomus formivorus are made of composites comprising micro- and submicron fibers

Our understanding of the extraordinary mechanical and physico-chemical properties of spider silk is largely confined to the fibers produced by orb-weaving spiders, despite the diversity of foraging webs that occur across numerous spider families. Crab spiders (Thomisidae) are described as ambush predators that do not build webs, but nevertheless use silk for draglines, egg cases and assembling leaf-nests. A little-known exception is the Australian thomisid Saccodomus formivorus, which constructs a basket-like silk web of extraordinary dimensional stability and structural integrity that facilitates the capture of its ant prey. We examined the physical and chemical properties of this unusual web and revealed that the web threads comprise microfibers that are embedded within a biopolymeric matrix containing additionally longitudinally-oriented submicron fibers. We showed that the micro- and submicron fibers differ in their chemical composition and that the web threads show a remarkable lateral resilience compared with that of the major ampullate silk of a well-investigated orb weaver. Our novel analyses of these unusual web and silk characteristics highlight how investigations of non-model species can broaden our understanding of silks and the evolution of foraging webs.

Testing the hypothesized antipredator defence function of stridulation in the spiny orb-weaving spider, Micrathena gracilis

The observable diversity of antipredator defences across organisms demonstrates predation's impact on trait evolution. The functions of many traits that are presumed to have an antipredator function have never been directly tested. The spiny orb-weaving spider, Micrathena gracilis, for example, stridulates when grasped. While stridulation was first hypothesized to be an antipredator defence nearly 50 years ago, no data exist to support this hypothesis. To explore the form and function of M. gracilis stridulation, we first quantified the behavioural and acoustical properties of sound production. Next, using laboratory assays, we directly tested the effect of stridulation on survival with an avian predator – blue jays, Cyanocitta cristata . Finally, we conducted a large mark–recapture field study in which we compared the natural survival of experimentally manipulated adult female M. gracilis that could not stridulate (silenced) versus could stridulate (control). Stridulatory pulses produced broadband frequency spectra, consistent with acoustic antipredator defences in other taxa. We also observed stridulation by male M. gracilis for the first time. In staged laboratory interactions with captive blue jays, we found no differences in survival between silenced and control M. gracilis . Similarly, in our mark–recapture field study, we found no differences in survival estimates between silenced and control groups, nor an effect of stridulation rate. While M. gracilis stridulation closely resembles antipredator stridulation in other arthropods, our behavioural data do not yet provide solid support for an antipredator function in M. gracilis . • We tested whether M. gracilis uses stridulation in antipredator defence. • We quantified behavioural and acoustical properties of stridulation. • We tested survival of silenced and control adult females in the laboratory/field. • Survival of silenced and control females did not differ. • Stridulation may not serve an antipredator function in M. gracilis.

Observing web damage response variability in Zygiella x-notata

The foraging success of orb-web spiders depends primarily on the structure and maintenance of their webs. The purpose of this study was to examine how the presence and degree of web damage affected web-building responses in Zygiella x-notata. Part 1 of the study investigated the severity of damage with: a control, a partial web damage group, and a complete web damage group. Part 2 investigated frequency of damage over a 5-day period with: a control group, an infrequent web damage group, and a frequent web damage group. Four spiders were allocated randomly to each experimental group, and four trials for each were conducted. Results suggested that spiders were unlikely to relocate, regardless of the type of web damage that occurred. Web sizes exhibited a decreasing trend for all experimental groups after web damage, except for controls and partial damage groups, with the largest decreases seen in frequent and complete damage groups. Anchor thread count increased after partial and complete damage; however, it decreased after damage in both repetitive web damage groups. Overall, these preliminary findings suggest that web-building spiders will likely rebuild instead of relocate in areas where damage occurs to their webs. When the damage is partial and non-repetitive, they expend more energy repairing and reinforcing their webs. However, when faced with repetitive and complete damage, their behavior is an adaptation to reduce the amount of energy expended in web repair.

Conspicuous colours in a polymorphic orb-web spider: evidence of predator avoidance but not prey attraction

Conspicuous colours in animals are usually explained by mate attraction, predator avoidance and prey attraction. Predators may lure prey by mimicking food or other resources. Alternatively, some animals avoid predation by visually signalling unpalatability to predators. The evolution of a signal is affected by receiver processing mechanisms. Therefore, variation in sensory systems may explain the evolution of colour polymorphism of conspicuous species. We aimed to investigate the role of receivers in the evolution and maintenance of colour conspicuousness and polymorphism in Gasteracantha cancriformis (Araneidae). We tested two hypotheses: (1) conspicuous coloration is a prey lure strategy; (2) conspicuous coloration is a warning signal to predators. Furthermore, we identified the taxonomic order of prey captured and the type of predator (avian versus arthropod). To assess the role of prey, we conducted a field experiment in which webs were assigned to one of four treatments: yellow, red or black spider models, or no model. For each treatment, we counted the number of prey trapped on the webs and calculated the damaged area of the webs. To assess the role of predators, we conducted a second field experiment in which we attached yellow, red and black models to trees using nylon thread and observed the number of attack markings on each model. Our results did not corroborate the prey attraction hypothesis. In the predation experiment, black models had more attack markings, indicating that yellow and red models were less preferred. This suggests that spider coloration may play a role in predator avoidance. Colour polymorphism in this species is possibly a multifunctional attribute, where some morphs benefit from aposematism, whereas others may have alternative fitness advantages. Nonadaptive explanations should also be considered in future experiments of the evolution and maintenance of colour polymorphisms.

Spidroin profiling of cribellate spiders provides insight into the evolution of spider prey capture strategies

Orb-weaving spiders have two main methods of prey capture: cribellate spiders use dry, sticky capture threads, and ecribellate spiders use viscid glue droplets. Predation behaviour is a major evolutionary driving force, and it is important on spider phylogeny whether the cribellate and ecribellate spiders each evolved the orb architecture independently or both strategies were derived from an ancient orb web. These hypotheses have been discussed based on behavioural and morphological characteristics, with little discussion on this subject from the perspective of molecular materials of orb web, since there is little information about cribellate spider-associated spidroin genes. Here, we present in detail a spidroin catalogue of six uloborid species of cribellate orb-weaving spiders, including cribellate and pseudoflagelliform spidroins, with transcriptome assembly complemented with long read sequencing, where silk composition is confirmed by proteomics. Comparative analysis across families (Araneidae and Uloboridae) shows that the gene architecture, repetitive domains, and amino acid frequencies of the orb web constituting silk proteins are similar among orb-weaving spiders regardless of the prey capture strategy. Notably, the fact that there is a difference only in the prey capture thread proteins strongly supports the monophyletic origin of the orb web.