The web repair behaviour of an orb spider

Investigating the Influence of Anthropogenic Activities on Behavioral Changes of an Orb Web Spider (Neoscona vigilans)

Orb web spiders are common and highly diversified animals found in almost all habitats. They have remarkable plasticity against biotic and abiotic factors, making them excellent indicators of environmental health. The web creation behavior of spiders is influenced by disturbances in the environment. The aim of this research was to observe the alteration in the web-building behavior of Neoscona vigilans caused by human activities, specifically traffic disturbances. Spider webs were located and photographed at nighttime along the roadside, and their web characteristics were calculated. Spiders were captured from webs for their body measurements. Spider fourth leg length, carapace width, and body length had a significant association with web size and diameter, CTL, capture area, and mesh size. The quantity of trapped prey, the height of the plant, and the foliage radius increased with the distance from the road. Conversely, anchor points and web elevation from the ground dropped. The highest and lowest proportions of anomalies (modifications/defects) were recorded as holes (52.7%) in 105 webs (100%) and supernumerary (0.7%) in 55 webs (52.4%), respectively. Road disturbance had a negative influence on the spider's behavior as the webs formed in close proximity to the road had a higher frequency of anomalies, with a gradual decrease distantly. We can gain further insight into how different environmental changes, disruptions, and pollutants lead to this imperfection in the otherwise flawless perfect structure of spider webs.

Promises and limits of an agency perspective in evolutionary developmental biology

An agent-based perspective in the study of complex systems is well established in diverse disciplines, yet is only beginning to be applied to evolutionary developmental biology. In this essay, we begin by defining agency and associated terminology formally. We then explore the assumptions and predictions of an agency perspective, apply these to select processes and key concept areas relevant to practitioners of evolutionary developmental biology, and consider the potential epistemic roles that an agency perspective might play in evo devo. Throughout, we discuss evidence supportive of agential dynamics in biological systems relevant to evo devo and explore where agency thinking may enrich the explanatory reach of research efforts in evolutionary developmental biology.

Biological challenges to conclusions from molecular phylogenies: behaviour strongly favours orb web monophyly, contradicting molecular analyses

This first-ever extensive review of the construction behaviour of orb webs, of webs secondarily derived from orbs, and of non-orbs shows that the evidence favouring monophyly over convergent evolution of orbs is stronger than previously appreciated. The two major orb-weaving groups, Uloboridae and Araneoidea, share 31 construction behaviour traits, 20 of which are likely to be both derived and to have feasible alternatives, making convergence an unlikely explanation. Convergence in two lineages seems unlikely, and convergence in five different lineages, as proposed in some recent molecular studies of phylogeny, is even less credible. A further set of seven shared responses in orb design to experimentally constrained spaces also supports orb monophyly. Finally, a ‘control’ case of confirmed convergence on similar ‘pseudo-orbs’ in a taxonomically distant group also supports this argument, as it shows a low frequency of behavioural similarities. I argue that the omission of behavioural data from recent molecular studies of orb web evolution represents a failure of the analytic techniques, not the data, and increases the risk of making mistakes. In general, phylogenetic studies that aim to understand the evolution of particular phenotypes can benefit from including careful study of the phenotypes themselves.

The Use of Tuning Forks for Studying Behavioural Responses in Orb Web Spiders

Simple Summary

Spiders are common predators found in almost every type of environment, and are used as model organisms in studies ranging from communication and signalling to biochemical studies on their silk. Orb spiders are particularly interesting, as their web provides a cost-effective way to obtain information on their foraging behaviour. However, studies on short-term behaviours including prey capture and escape behaviours are rare and usually take place in artificial settings, such as laboratories. In this study, we tested a simple methodology using tuning forks that can be used consistently and reliably in the field. The two tuning forks are capable of producing attack (440 Hz) and escape (256 Hz) responses from the spiders. We also used a metal wire as a mechanical stimulus for comparison, which as predicted, was less reliable. We demonstrate the usefulness of the methodology by quantitatively investigating how the size of the spider and the size of its web affect predatory and escape response rates in the autumn spider, although no significant effects of either were found. However, our results confirm the ease by which this simple method can be used to conduct behavioural studies of orb spiders in the wild.

Abstract

Spiders and their webs are often used as model organisms to study a wide range of behaviours. However, these behavioural studies are often carried out in the laboratory, and the few field studies usually result in large amounts of video footage and subsequent labour-intensive data analysis. Thus, we aimed to devise a cost- and time-effective method for studying the behaviour of spiders in the field, using the now almost forgotten method of stimulating webs with tuning forks. Our study looked at the viability of using 256 Hz and 440 Hz tuning forks to stimulate, anti-predatory and predatory responses in the orb web spider Metellina segmentata, respectively. To assess the consistency of the behaviours produced, we compared these to direct mechanical stimulation with a metal wire. The results suggest that the tuning forks produce relatively consistent behaviours within and between two years in contrast to the metal wire. We furthermore found no significant effects of spider length or web area on spider reaction times. However, we found significant differences in reaction times between escape and prey capture behaviours, and between tuning forks and the wire. Thus, we demonstrated the potential of tuning forks to rapidly generate quantitative data in a field setting.

Body size and tree species composition determine variation in prey consumption in a forest-inhabiting generalist predator

Trophic interactions may strongly depend on body size and environmental variation, but this prediction has been seldom tested in nature. Many spiders are generalist predators that use webs to intercept flying prey. The size and mesh of orb webs increases with spider size, allowing a more efficient predation on larger prey. We studied to this extent the orb-weaving spider Araneus diadematus inhabiting forest fragments differing in edge distance, tree diversity, and tree species. These environmental variables are known to correlate with insect composition, richness, and abundance. We anticipated these forest characteristics to be a principle driver of prey consumption. We additionally hypothesized them to impact spider size at maturity and expect shifts toward larger prey size distributions in larger individuals independently from the environmental context. We quantified spider diet by means of metabarcoding of nearly 1,000 A. diadematus from a total of 53 forest plots. This approach allowed a massive screening of consumption dynamics in nature, though at the cost of identifying the exact prey identity, as well as their abundance and putative intraspecific variation. Our study confirmed A. diadematus as a generalist predator, with more than 300 prey ZOTUs detected in total. At the individual level, we found large spiders to consume fewer different species, but adding larger species to their diet. Tree species composition affected both prey species richness and size in the spider's diet, although tree diversity per se had no influence on the consumed prey. Edges had an indirect effect on the spider diet as spiders closer to the forest edge were larger and therefore consumed larger prey. We conclude that both intraspecific size variation and tree species composition shape the consumed prey of this generalist predator.

Xanthurenic Acid Is the Main Pigment of Trichonephila clavata Gold Dragline Silk

Spider silk is a natural fiber with remarkable strength, toughness, and elasticity that is attracting attention as a biomaterial of the future. Golden orb-weaving spiders (Trichonephila clavata) construct large, strong webs using golden threads. To characterize the pigment of golden T. clavata dragline silk, we used liquid chromatography and mass spectrometric analysis. We found that the major pigment in the golden dragline silk of T. clavata was xanthurenic acid. To investigate the possible function of the pigment, we tested the effect of xanthurenic acid on bacterial growth using gram-negative Escherichia coli and gram-positive Bacillus subtilis. We found that xanthurenic acid had a slight antibacterial effect. Furthermore, to investigate the UV tolerance of the T. clavata threads bleached of their golden color, we conducted tensile deformation tests and scanning electron microscope observations. However, in these experiments, no significant effect was observed. We therefore speculate that golden orb-weaving spiders use the pigment for other purposes, such as to attract their prey in the sunlight.

Urbanization-driven changes in web building and body size in an orb web spider

In animals, behavioural responses may play an important role in determining population persistence in the face of environmental changes. Body size is a key trait central to many life-history traits and behaviours. Correlations with body size may constrain behavioural variation in response to environmental changes, especially when size itself is influenced by environmental conditions. Urbanization is an important human-induced rapid environmental change that imposes multiple selection pressures on both body size and (size-constrained) behaviour. How these combine to shape behavioural responses of urban-dwelling species is unclear. Using web building, an easily quantifiable behaviour linked to body size and the garden spider Araneus diadematus as a model, we evaluated direct behavioural responses to urbanization and body size constraints across a network of 63 selected populations differing in urbanization intensity. We additionally studied urbanization at two spatial scales to account for some environmental pressures varying across scales and to obtain first qualitative insights about the role of plasticity and genetic selection. Spiders were smaller in highly urbanized sites (local scale only), in line with expectations based on reduced prey biomass availability and the Urban Heat Island effect. Web surface and mesh width decreased with urbanization at the local scale, while web surface also increased with urbanization at the landscape scale. The latter two responses are expected to compensate, at least in part, for reduced prey biomass availability in cities. The use of multivariate mixed modelling reveals that although web traits and body size are correlated within populations, behavioural responses to urbanization do not appear to be constrained by size: there is no evidence of size-web correlations among populations or among landscapes, and web traits appear independent from each other. Our results demonstrate that responses in size-dependent behaviours may be decoupled from size changes, thereby allowing fitness maximization in novel environments. The spatial scale at which traits respond suggests contributions of both genetic adaptation (for web investment) and plasticity (for mesh width). Although fecundity decreased with local-scale urbanization, A. diadematus abundances were similar across urbanization gradients; behavioural responses thus appear overall successful at the population level.

The Effect of Wind Exposure on the Web Characteristics of a Tetragnathid Orb Spider

Studies on spiders in their natural habitats are necessary for determining the full range of plasticity in their web-building behaviour. Plasticity in web design is hypothesised to be important for spiders building in habitats where environmental conditions cause considerable web damage. Here we compared web characteristics of the orb spider Metellina mengei (Araneae, Tetragnathidae) in two different forest habitats differing in their wind exposure. We found a notable lack of differences in web geometry, orientation and inclination between webs built along an exposed forest edge and those built inside the forest, despite marked differences in wind speed. This suggests that M. mengei did not exhibit web-building plasticity in response to wind in the field, contrasting with the findings of laboratory studies on other species of orb spiders. Instead, differences in prey capture and wind damage trade-offs between habitats may provide an explanation for our results, indicating that different species employ different strategies to cope with environmental constraints.

A bioinspired adaptive spider web

This work presents an adaptive structure inspired by spider webs' behavior. To investigate the dynamic properties and performance of this system, numerical models are developed to examine the effects of pretension in radial strings, and Young's modulus, and damping ratio on the natural frequency and total energy of the system. An experimental study was conducted to validate theoretical results. Stepper motors controlled by a microcontroller are utilized to increase the pretension in the radial strings of the web in order to tune the web's energy absorption ability. It is demonstrated that the pretension, Young's modulus, and damping ratio in the radial strings can significantly affect the natural frequency and total energy of full and damaged webs. It is also shown that increasing the pretension in the radial strings compensates for the loss of stiffness due to the damaged strings. Finally, it is shown that controlling the pretension in radial strings can provide higher energy absorption capability for the spider web.

The secondary frame in spider orb webs: the detail that makes the difference

Spider orb webs are multifunctional structures, the main function of which is to dissipate the kinetic energy of the impacting prey, while minimizing structural damage. There is no single explanation for their remarkable strength and ductility. However, it is clear that topology is decisive in the structural performance upon impact, and the arrangement of the different silk threads in the web must also exert an effect. The aim of this study is to show how a slight variation in the geometry markedly affects the prey-capture ability of spider orb webs. The study is focused on the secondary frame, a thread interposed between radial and primary frame strands, the importance of which has not been examined until now. The simulation of the impact performance of webs using different lengths of the secondary frame clarifies its structural role, which has proven to be decisive. Furthermore, the study explains why secondary frame threads of moderate length, as commonly encountered, enable the capture of prey with higher energy without a marked increase in the volume of silk used.

Large orb-webs adapted to maximise total biomass not rare, large prey

Spider orb-webs are the ultimate anti-ballistic devices, capable of dissipating the relatively massive kinetic energy of flying prey. Increased web size and prey stopping capacity have co-evolved in a number orb-web taxa, but the selective forces driving web size and performance increases are under debate. The rare, large prey hypothesis maintains that the energetic benefits of rare, very large prey are so much greater than the gains from smaller, more common prey that smaller prey are irrelevant for reproduction. Here, we integrate biophysical and ecological data and models to test a major prediction of the rare, large prey hypothesis, that selection should favour webs with increased stopping capacity and that large prey should comprise a significant proportion of prey stopped by a web. We find that larger webs indeed have a greater capacity to stop large prey. However, based on prey ecology, we also find that these large prey make up a tiny fraction of the total biomass (=energy) potentially captured. We conclude that large webs are adapted to stop more total biomass, and that the capacity to stop rare, but very large, prey is an incidental consequence of the longer radial silks that scale with web size.