Web Construction Research Articles

Plant–herbivore–natural enemy trophic webs in date palm agro-ecosystems

Understanding the composition and dynamics of ecological communities is challenging because of the large number of organisms present and their numerous interactions. Among agricultural systems, intercropping considerably increases the complexity of communities compared to monocultures and alternative host plants can influence insect pest damage. Using literature records, we construct and analyse connectance trophic webs of date palm (Phoenix dactylifera) agro-ecosystems, including and excluding intercrops. Estimates of connectance (community complexity) are relatively low and little affected by consideration of intercrops. Plant–herbivore overlap is relatively high, suggesting that herbivores are typically not specialists. Herbivore–natural enemy overlap is greater when intercrops are considered, suggesting that diffuse apparent competition regulates pest populations. We pay particular attention to how trophic web structure might affect Batrachedra amydraula (Lesser date moth), an important economic pest. Records indicate it having 15 species of natural enemies and sharing 9 of these with other herbivores; these may maintain populations of natural enemies when the moth is seasonally rare, contributing to pest suppression. The estimated potential for apparent competition between the lesser date moth and other herbivores is higher when intercrops are considered. The consequent expectation of less severe infestations in plantations that are intercropped compared to monocultures matches empirically derived reports. Further, comparing results obtained from the literature on one country (Oman) and from 15 Middle Eastern countries, we find that community metric estimates are relatively little affected by the geographical scale considered. Overall, our results suggest that literature-based trophic web construction can provide an efficient and robust alternative, or in addition, to direct empirical methodologies and that the presence of intercrops will contribute to major pest suppression via indirect apparent competition.

Understanding the habitat selection and natural history of the spider Deinopis cf. cylindracea (Deinopidae).

Habitat choice is fundamental for an animal foraging, defense, and reproduction. Ogre-faced spiders are known for their unusual morphology, natural history, and rarity. They are sit-and-wait predators that build net-like webs that are manipulated by spiders and thrown at their prey. Hunting behavior includes selecting microhabitats for web construction that reduces the likelihood of damage or entanglement in the substrate during prey capture. Therefore, we expect that Deinopis cf. cylindracea selects smooth surfaces to forage on. We observed D. cf. cylindracea associated with smooth trunks of Plinia cauliflora (Myrtaceae) in the natural environment and actively selecting smooth trunks over rough trunks or litter in controlled experiments. Such selection is likely to maximize the foraging strategy of launching the web towards the substrate. Aggregations had occurred more often in the 50 cm trunk closest to the ground, where the prey community is largest. During the day, this spider appears to choose sites where it can adopt a stick-like posture upon the vegetation near the ground. Hunting at night and resting cryptically during the day appears to be shaped by natural selection for the survival and reproduction of this spider species.

Temporal variation in spider trophic interactions is explained by the influence of weather on prey communities, web building and prey choice

Generalist invertebrate predators are sensitive to weather conditions, but the relationship between their trophic interactions and weather is poorly understood. This study investigates how weather affects the identity and frequency of spider trophic interactions over time, alongside prey community structure, web characteristics and prey choice. Spiders (Linyphiidae and Lycosidae) and their prey were collected from barley fields in Wales, UK, from April to September 2017–2018. The gut contents of 300 spiders were screened using DNA metabarcoding, analysed via multivariate models and compared against prey availability using null models. When linyphiids were collected from webs, the height and area of webs were recorded and compared against weather conditions. Trophic interactions changed over time and with weather conditions, primarily related to concomitant changes in prey communities. Spiders did, however, appear to mitigate the effects of structural changes in prey communities through changing prey preferences according to prevailing weather conditions, possibly facilitated by adaptive web construction. Using these findings, we demonstrate that prey choice data collected under different weather conditions can be used to refine inter‐annual predictions of spider trophic interactions, although prey abundance was secondary to diversity in driving the diet of these spiders. By improving our understanding of the interaction between trophic interactions and weather, we can better predict how ecological networks are likely to change over time in response to variation in weather conditions and, more urgently, global climate change.

Web construction behavior of Deinopis cf. cylindracea (Deinopidae: Araneae) and its comparison to webs of other Deinopidae

Deinopid spiders use highly specialized webs composed of a triangular non-sticky scaffolding (NS scaffolding) containing three radii and a modified orbicular web with a rectangular shape to capture prey. Spiders actively manipulate their webs to capture prey. We describe the web construction behavior of Deinopis cf. cylindracea and compare it and the shape of the sticky silk spiral (SS spiral) of other deinopid species using images in the literature and on the Internet. The web-building behavior in D. cf. cylindracea follows the pattern previously described for other species of Deinopis MacLeay, 1839. Web construction takes approximately 15 min in D. cf. cylindracea and has two stages: NS scaffolding construction and SS spiral construction. The final structure of the SS spiral has four closely spaced capture cords, five placed further apart, three near the top of the web, and two cords on the handles, making a total of 12. Other species of Deinopis have different numbers of cords. Finally, a novel finding is that the youngest spiders do not make webs with sticky lines, but instead use a simplified web to lunge forward, using only their legs to contact prey. To our knowledge, such behavior has never been described in this or any other group.

Water webbing: Long‐jawed spider (Araneae, Tetragnathidae) produces webs that touch the surface of ephemeral waterbodies

AbstractFew spiders are known to construct silk webs that physically contact water, despite it being both a surface and medium that can be exploited for web construction. Herein, we report on an Australian long‐jawed spider from the Tetragnatha genus (Tetragnatha cf. nitens) that frequently produces aerial webs that touch the surface of ephemeral waterbodies. Field observations revealed webs that were built by these spiders at varying heights above water in emergent vegetation stands around the edge of ephemeral waterbodies. Approximately, 15 of the 100 webs recorded were constructed immediately above the water with their lower sections making physical contact with the water's surface. We observed water striders becoming stuck within these low‐lying webs, suggesting that associating webs with surface water allows the spiders to exploit prey types that cannot be passively filtered from the environment in purely aerial webs. This could suggest that some species of long‐jawed spider select the positioning of their webs above water, which would be adaptive if it allows them to target different and possibly multiple prey communities.

The primary webs of Uloboridae (Araneae)

“Primary” webs of uloborids have large numbers of very fine lines and usually lack sticky cribellum silk. This paper reviews their taxonomic distribution (19 species in 5 genera) and the ontogenetic stages in which primary webs are built (spiderlings newly emerged from the egg sac, older juveniles, mature males, and normal and senile females), expands the knowledge of construction behavior, and describes several previously unnoticed design details. Primary webs differ from typical uloborid orbs in several ways: large numbers of fine radial and non-radial lines; facultative hub removal and replacement; usually closely spaced temporary spiral loops; and lines beyond the frame lines. Construction of supplemental radii in primary webs is distinctive in several respects: break and reel construction; tendencies to lay successive radii either on opposite sides of the web or close together in the same sector; high frequencies of aborted trips from the hub to the frame; production of multiple lines during a single trip from the hub to the frame and back; long pauses during the production of single radii; and variation in the sequences in which radial lines are added to a given sector. Some aspects of primary web construction resemble araneoid rather than typical uloborid behavior. The relation between primary webs and the evolution of orb webs, and the mechanism that spiders use to produce abundant non-radial lines despite making only radial movements during web construction remain uncertain. We speculate that primary webs are favored when spiders are unable to afford the costs of producing cribellate silk for a typical orb.

Feeding mediated web-building plasticity in a cobweb spider.

Behavioral plasticity has been proposed as a means by which animals alter their phenotypes in response to changing conditions. Animals may display behavioral plasticity as a consequence of environmental variation. The detritus-based, bell-shaped cobweb spider Campanicola campanulata is an ideal model to study behavioral plasticity, because its web architecture is easy to be quantified, and the functions of different parts of the web are clear. Though the plasticity of cobweb architecture has been reported in a few species, retreats as important defensive structures have rarely been considered before because retreats in most cobwebs are relatively small compared with the web size. We studied the web-building behaviors of C. campanulata under different feeding regimes. We set up 3 spider treatments with different feeding conditions: marginally well fed, moderately well fed, and extremely well fed, and observed the differences in the web architecture among them. In addition, we measured the mechanical properties of anchor silk, and also calculated the foraging and defense investment of the spiders. The results showed that marginally well-fed spiders build cobwebs with significantly longer length of anchor silk, lower retreat to the ground, more number and longer gumfooted lines, and larger capture area, while extremely well-fed spiders build cobwebs with significantly bigger retreat volume and higher height of retreat to the ground. In addition, marginally well-fed spiders invest significantly less during cobweb construction. However, there was no significant difference between the breaking force and elongation at break in anchor silk among different treatments. These results demonstrated that marginally well-fed spiders invest more in foraging, and extremely well-fed spiders invest more in defense, and the spider made a balance between foraging and predator avoidance in response to changes in physiological state. Our study strengthens the current understanding of web construction in cobweb spiders, especially those facing high costs during retreat construction.

Effects of resource availability on the web structure of female western black widows: is the web structure constrained by physiological trade-offs?

AbstractA major challenge of biological research is to understand what generates and maintains consistent behavioral variation among animals. Time and energy trade-offs, where expressing one behavior is achieved at the expense of another, are often suggested to favor the maintenance of behavioral differences between individuals. However, few studies have investigated how individuals adjust their allocation to different functions over time and depending on resource abundance. Black widow spiders of the genus Latrodectus build persistent webs that include structural threads which protect against predators and sticky trap threads to capture prey. Web structure consistently differs among individuals in the number of trap and structural threads. To quantify the intensity of a trade-off, we assessed the relationship between the number of structural and trap threads and tested whether varying food abundance affected individual differences in web structure. We further quantified how these individual differences change over time and with food abundance. We subjected spiders to three different levels of prey abundance and monitored the structure of their webs every twelve hours. We found no evidence for a trade-off between trap and structural threads. Instead, spiders that produced more structural threads also produced more trap threads, showing that spiders invested equally in both types of threads. Interestingly, the magnitude of individual differences in web structure was greatest when spiders were fed ad libitum and at the beginning of web construction. We suggest that variation in web structure between spiders could be the result of stable developmental differences in morphology or genetic differences.

Brownification of freshwater promotes nitrogen-cycling microorganism growth following terrestrial material increase and ultraviolet radiation reduction

Brownification is an increasingly concerning phenomenon faced by aquatic ecosystems in the changing environments, and the microbiome plays an irreplaceable role in material circulation and food web construction. Insight into the influence of brownification on microbial communities is crucial from an ecological standpoint. In this study, we simulated brownification using a the mesocosm system and explored the relationship between the characteristics of microbial communities and brownification using excitation-emission matrix (EEM) fluorescence spectroscopy and ultraviolet (UV) spectroscopy combined with high-throughput amplicon sequencing techniques. The results showed that brownification reduced the richness of the microbial community and selectively promoted the growth of nitrogen-cycling microorganisms, including hgcI_clade, Microbacteriaceae, and Limnohabitans. Brownification affected microbial communities by altering the carbon source composition and underwater spectrum intensity; UV, blue, violet, and cyan light were significantly (p < 0.05) correlated with microbial community richness, and random forest analysis revealed that UV, C1 (microbial humic-like), and C3 (terrestrial humic-like) were the major factors significantly influencing microbiome variation. We found that brownification affected microorganisms in shallow lakes, especially nitrogen cycling microorganisms, and propose that controlling terrestrial material export is an effective strategy for managing freshwater brownification.

Assessing the Importance of Chemosensory Cues in Web-Building Spiders

Spiders rely on chemosensory cues to help locate prey, evade predators, and select mates. This reliance on chemosensory detection makes spiders an ideal organism for inquiry-based projects that students can design and conduct on a shoestring budget. This investigation, designed for secondary education grades (6–12), encourages students to examine whether chemosensory cues influence web construction of harmless female spiders collected from backyard habitats. Students work in groups to develop hypotheses that they later test by introducing spiders into a simple T-maze containing some mix of chemosensory cues. To pilot this study, I designed two experiments to determine how female spiders construct their webs in response to chemosensory cues of potential prey or dangerous fire ants. The data from both projects were compiled and statistically analyzed using open-source software available online. In a classroom or laboratory setting, your students can work in groups to develop their own hypotheses, design and run their experiments, and statistically analyze their results using the same free software. Although simple in design, this activity provides students with an opportunity to develop novel lines of research inquiry and engage in the practice of science.

A Semantic Ontology-Based Approach to Support Model-Based Systems Engineering Design for an Aircraft Prognostic Health Management System

The Prognostic and Health Management (PHM) system of an aircraft has complex structures and diverse functions. It is highly coupled with other systems, such as the avionics system and flight management system. The Model-based Systems Engineering (MBSE) method is effective to support the design and verification of the aircraft PHM system. As a powerful semantic web construction method, ontology has been widely used to express design information, such as the concepts and the relationships between them. However, traditional graphical MBSE models have a natural weakness in transforming into ontology. In this paper, a semantic MBSE method is proposed to support the transform of the ontology model. Firstly, according to the design characteristics of the aircraft PHM system, a meta-model library of the aircraft PHM system is developed to support the design and evaluation. An MBSE modeling method based on requirement analysis, function analysis, logical architecture design, and physic architecture design is applied in the PHM design process. Secondly, the semantic system modeling language KARMA based on “graph, object, property, point, relationship, role, and extension” (GOPPRRE) is used to transfer the graphical MBSE model to the semantic MBSE model, which can be easily transformed to an ontology model. Finally, an ontology based on semantic modeling is developed to describe the MBSE entities and to support MBSE design. In this paper, a case study of an aircraft fuel PHM system is carried out to validate the proposed method. Based on the developed meta-model library, a complete MBSE design process for the aircraft PHM system is realized. And then an ontology model supporting PHM system design is generated from the semantic MBSE model. The MBSE ontology provides a shareable capability to help designers communicate effectively. Quantitative analysis based on ontology is also provided to verify the complexity and scale of the MBSE design process. Moreover, logical reasoning ability can also be provided to support the early requirement traceability for MBSE design. In general, the case study results show the feasibility and effectiveness of the proposed method for the aircraft PHM system design.

Typical scaled food web structure and total mercury enrichment characteristics in Xingkai Lake, China.

Different from the widely used constant discrimination factor Δ15N = 3.4‰ between two adjacent trophic positions (TPs), a scaled Δ15N framework for evaluating the TP of species was developed in 2014, that is, the Δ15N between two adjacent TPs decreases as the TP increases which is considered to be in closer conformity to the trophic cascade in the natural food web. In this study, we compared the two TP calculation methods and then reconsidered the evaluation of the trophic magnification factors (TMFs). Our results show that the TPscaled value is higher and the TMFs value is lower under the scaled Δ15N framework, indicating that the TMFs value under the constant Δ15N framework is often overestimated. We further constructed a diet proportion food web model, which shows that species with lower TP has higher contribution rate as food sources. In Xingkai Lake, the enrichment process of mercury in the food web is not strictly consistent with the diet proportion of the food web. Based on the diet proportion food web model and the mercury enrichment model, it can be found that the White shrimp (Exopalaemon modestus) is not only an important food source, but also the main source of mercury transmission in the food web. Overall, our findings have quantified the food web construction and thus facilitated a better understanding of the interaction between the diet proportion and the bio-concentration in the food web.

Web building behavior in a wall spider (Oecobiidae) suggests a close relationship with orb-weavers

Behavior is often phylogenetically informative and detailed descriptions of behavior have been used to support taxonomic relationships in several groups, such as birds, lizards, and arthropods. Web building behavior has provided informative traits to several spider families, but observations are lacking for other families, such as wall spiders Oecobiidae. Recent phylogenetic hypotheses based on molecular traits placed oecobiids either close to cribellate orb weavers (Uloboridae) or to long-spinneret spiders (Hersiliidae). Here, we describe for first time the web construction behavior and details of the web design in the oecobiid Oecobius concinnus Simon 1893 (Oecobiidae). We compare them with uloborid and araneoid orb weavers. If Oecobiidae and Uloboridae are closely related, we expect that O. concinnus share some web construction behaviors with these orb weavers. Video recordings and analyses of web structures suggest the sequence of web construction (radii, then sticky spiral construction) and the arrangement of cribellate threads are possible homologies between Oecobiidae and orb weavers, supporting a close relationship of Oecobiidae with Uloboridae.

The orb-weaver's step-by-step guide to homebuilding

It's hard to believe that the intricate patterns of fine silk we call cobwebs are each constructed by a single spider. They diligently design and build homes strong enough to stop an insect in its tracks. A team of researchers at Johns Hopkins University, USA, led by Andrew Gordus, set out to characterize the way orb-weavers, Uloborus diversus, construct such exquisite webs by closely analyzing the spiders' movements while they build.To observe the spiders' skills up close, the researchers outfitted a chamber with a video camera looking down onto a plexiglass box. They then annotated a portion of video, frame by frame, labelling the body, legs and joints so that they could adapt algorithms to predict where the legs and body would be in the rest of the videos. Using this approach, the researchers characterized each spider's movements as they spun their webs.It turns out that web assembly is made up of four previously defined construction phases: proto-web, radii, auxiliary and capture. In the initial stage of a web the spider builds a proto-web, which serves as scaffolding and looks like a messy tangle. The spiders paused most often while building the proto-web, suggesting that they use this time to assess the integrity of their composition. During the radii stage the spiders removed much of the proto-web and anchored silk between the edges and the center hub. Following the radii stage, the spiders built an auxiliary web, which is a single spiral that sweeps out from the hub to the edge of the web. And finally, the spiders removed the auxiliary spiral during the final capture stage, when the spider spun silk around the radii spiralling in tightly toward the center.By tracking the spiders' limbs, the research team distinguished behaviors such as walking, moving right or left legs, and pulling silk quickly or slowly. When they organized these behaviors by construction phase, they saw that particular behaviors are more likely to occur at some stages than others, such as leg sweeps during capture and increased pausing while building the proto-web. By tracking the position of the spider, they predicted when the spider was building radii by the straight walks from the center to the edge and back again. They then analyzed transitions between behaviors by calculating the probability that one behavior will follow another. They found that although each stage is made up of similar sets of behaviors, the probability that one will follow another is different for each stage. For example, during the capture stage, a fast silk pull is likely to follow multiple different behaviors, whereas during the radii stage, slow silk pulls are more common.Finally, the team used a mathematical model to test if the spiders' motions were distinct enough to predict the stage based on the probability of movements and transitions between movements. They found that their model successfully predicted different stages except for the proto and radii stage, which the model did not differentiate well. The researchers interpreted this outcome to mean that spiders move similarly while building the proto-web and the radii but the different patterns of web construction result from where the spider is on the web.A close and careful investigation of orb-weavers honing their craft shows that even a complex masterpiece like a spiderweb is ultimately made by an individual's flexible execution of a limited set of repeated movements.

Orb weavers: Patterns in the movement sequences of spider web construction

Quantitative behavior analyses of spider movements- large and small- reveal repeated action sequences that define stages of web building.

Distinct movement patterns generate stages of spider web building

The geometric complexity and stereotypy of spider webs have long generated interest in their algorithmic origin. Like other examples of animal architecture, web construction is the result of several assembly phases that are driven by distinct behavioral stages coordinated to build a successful structure. Manual observations have revealed a range of sensory cues and movement patterns used during web construction, but methods to systematically quantify the dynamics of these sensorimotor patterns are lacking. Here, we apply an analytical pipeline to quantify web-making behavior of the orb-weaver Uloborus diversus. Position tracking revealed stereotyped stages of construction that could occur in typical or atypical progressions across individuals. Using an unsupervised clustering approach, we identified general and stage-specific leg movements. A hierarchical hidden Markov model revealed that web-building stages are characterized by stereotyped sequences of actions largely shared across individuals, regardless of whether these stages progress in a typical or an atypical fashion. Web stages could be predicted based on action sequences alone, revealing that web-stage geometries are a physical manifestation of behavioral transition regimes.

In situ three-dimensional spider web construction and mechanics

Spiders are nature's engineers that build lightweight and high-performance web architectures often several times their size and with very few supports; however, little is known about web mechanics and geometries throughout construction, especially for three-dimensional (3D) spider webs. In this work, we investigate the structure and mechanics for a Tidarren sisyphoides spider web at varying stages of construction. This is accomplished by imaging, modeling, and simulations throughout the web-building process to capture changes in the natural web geometry and the mechanical properties. We show that the foundation of the web geometry, strength, and functionality is created during the first 2 d of construction, after which the spider reinforces the existing network with limited expansion of the structure within the frame. A better understanding of the biological and mechanical performance of the 3D spider web under construction could inspire sustainable robust and resilient fiber networks, complex materials, structures, scaffolding, and self-assembly strategies for hierarchical structures and inspire additive manufacturing methods such as 3D printing as well as inspire artistic and architectural and engineering applications.

Differences in web structure of Tetragnatha tenuissima (Araneae: Tetragnathidae) due to environmental conditions

Spiders can modify their web construction behaviour according to environmental conditions. Here, we examined how the web structure of Tetragnatha tenuissima differentiates depending on habitat type (swamp or river edge) at La Selva Biological Station, Costa Rica. We characterized the web architecture based on length, number of radii, and the spiral spacing relative to web length. There were no significant differences on the length or number of radii between the webs present in the swamp and river habitats. In terms of the spiral spacing relative to web length, there was a significant difference between habitats, with less distance in river-side webs than in the ones on swamps. This could be explained by the potential differential resource availability on each environment. Therefore, habitat type appears as an explanatory variable for differences on the web structure of T. tenuissima. Due to the small number of identifiable individuals of other Tetragnatha species, the effect of congeneric species co-occurrence on web structure remains as a factor to be tested in future research.

Complex behavioral plasticity is not reduced in spiderlings with miniature brains.

The brains of smaller animals are smaller than those of their larger relatives, but it is not clear whether their adaptive behavioral flexibility is more limited. Previous interspecific comparisons found that aspects of web construction behavior of very small orb weaving spiders (0.005 mg) were no less precise than those of much larger related orb weavers (30 mg), but the behaviors tested were relatively simple. Here we perform a more sensitive intraspecific test involving the multiple behavioral adjustments of orb web designs made by Leucauge argyra to confinement in very small spaces. Web adjustments of spiderlings as small as ~0.1 mg were compared to previously published observations of ~80 mg conspecific adults. Spiderlings in constrained spaces made all of the complex adjustments made by adults in at least seven independent web design variables, and their adjustments were no less precise. Rough estimates based on previously published data on total brain volumes and the mean diameters of neuron cell bodies suggested that spiderlings and adult females of Leucauge may have similar numbers of neurons, due to spiderlings having smaller neurons and a greater percentage of body tissues dedicated to the brain. We speculate that this neural similarity may explain why L. argyra spiderlings showed no behavioral deficits compared with adults.

RNA-Seq analysis of the blue light-emitting Orfelia fultoni (Diptera: Keroplatidae) suggest photoecological adaptations at the molecular level

Bioluminescence in Diptera is found in the Keroplatidae family, within Arachnocampininae and Keroplatinae subfamilies, with reported occurrences in Oceania, Eurasia, and Americas. Larvae of Orfelia fultoni, which inhabit stream banks in the Appalachian Mountains, emit the bluest bioluminescence among insects, using it for prey attraction, similarly to Arachnocampa spp. Although bioluminescence has a similar prey attraction function, the systems of Arachonocampininae and Keroplatinae subfamilies are morphologically/biochemically distinct, indicating different evolutionary origins. To identify the possible coding genes associated with physiological control, ecological adaptations, and origin/evolution of bioluminescence in the Keroplatinae subfamily, we performed the RNA-Seq analysis of O. fultoni larvae during day and night and compared it with the transcriptomes of Arachnocampa luminosa, and reanalyzed the previously published proteomic data of O. fultoni against the RNA-Seq dataset. The abundance of chaperones/heat-shock and hexamerin gene products at night and in luciferase enriched fractions supports their possible association and participation in bioluminescence. The low diversity of copies/families of opsins indicate a simpler visual system in O. fultoni. Noteworthy, gene products associated with silk protein biosynthesis in Orfelia were more similar to Lepidoptera than to the Arachnocampa, indicating that, similarly to the bioluminescent systems, at some point, the biochemical apparatus for web construction may have evolved independently in Orfelia and Arachnocampa.