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Many spider orb-webs are exposed to sunlight and the potentially damaging effects of ultraviolet B (UVB) radiation. We examined the effect of UVB on the viscoelastic glycoprotein core of glue droplets deposited on the prey capture threads of these webs, hypothesizing that webs built by species that occupy sunny habitats are less susceptible to UVB...
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... line deflection angles ( Fig. 2; supplementary material Table S1) are an estimation of the force on droplets and were measured just prior to droplet extension (0% DE) and at 25%, 50%, 75% and 99% of DE. By combining these angles with values for the diameter and Young's modulus of each species' paired axial lines, we computed the force on an extending droplet (Tables 4, 5). ...
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An orb web’s prey capture thread features tiny glue droplets, each formed of an adhesive glycoprotein core surrounded by an aqueous layer. Small molecules in the aqueous layer confer droplet hygroscopicity and maintain glycoprotein viscoelasticity, causing droplet volume and glycoprotein performance to track changes in environmental humidity. Dropl...
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... 29 Since then, the spontaneous formation of droplets by fibrous materials has attracted attention of biologists and engineers. 1,[15][16][17][30][31][32] While the Plateau instability received great attention from fluid mechanicians and materials scientists, 33,34 a rigorous classification of axisymmetric shapes of droplets on fibers is lacking. Yet, it is in high demand. ...
With the developments in nanotechnology, nanofibrous materials attract great attention as possible platforms for fluidic engineering. This requires an understanding of droplet interactions with fibers when gravity plays no significant role. This work aims to classify all possible axisymmetric configurations of droplets on fibers. The contact angle that the drop makes with the fiber surface is allowed to change from 0° to 180°. Nodoidal apple-like droplets with inverted menisci cusped toward the droplet center and unduloidal droplets with menisci cusped away from the droplet center were introduced and fully analyzed. The existing theory describing axisymmetric droplets on fibers is significantly enriched introducing new morphological configurations of droplets. It is experimentally shown that the barreled droplets could be formed on non-wettable fibers offering contact angles greater than 90°. The theory was quantitatively confirmed with hemispherical droplets formed at the end of a capillary tube and satisfying all the boundary conditions of the model. It is expected that the developed theory could be used for the design of nanofiber-based fluidic devices and for drop-on-demand technologies.
... Thus, the contact angle is not a constant, but it depends on the prehistory of liquid flow. Material engineers wonder which contact angle to choose for the design of the fibrous materials such as protective masks, filters or microfluidic devices [1,[3][4][5]9,[13][14][15][16][17][18]? ...
... As explained more fully in previous studies 33,35,43,64,65 , in the laboratory we used tweezers whose tips were covered in double-sided carbon tape (Cat #77816, Electron Microscope Sciences, Hatfield PA, USA) and blocked open to accommodate the spacing of U-shaped brass supports epoxied at 4.8 mm intervals to microscope slides with their free ends extending upward and covered with double-sided carbon tape ( Determining glycoprotein volume. All droplet and glycoprotein measurements as well as all droplet extensions were conducted at 23 °C and 55% relative humidity. ...
... All droplet and glycoprotein measurements as well as all droplet extensions were conducted at 23 °C and 55% relative humidity. Using previously described techniques 33,35,43,64,65 , we determined the volumes of three droplets and their glycoprotein cores, using each individual's mean values in statistical analyses. Mean values of the measurements used in these computations are reported in Supplementary Table 1. ...
... droplet volume glycoprotein volume droplet volume 100 (2) extending droplets. Three droplets from each web position were individually extended to pull-off as described previously 33,35,43,64,65 (Fig. 1D). This was done by first cleaning the 413 µm wide, polished steel tip of a probe with 100% ethanol, bringing it into contact with a droplet located at the center of a 4800 µm thread span, pressing the droplet against the probe until its support line was deflected by 500 μm, anchoring the probe, and then using a stepping motor to advance the X-axis of the Mitutoyo FS60 inspection microscope (Mitutoyo America Corp., Aurora IL, USA) stage on which the thread observation chamber rested, thus extending the droplet. ...
An orb web’s prey capture thread relies on its glue droplets to retain insects until a spider can subdue them. Each droplet’s viscoelastic glycoprotein adhesive core extends to dissipate the forces of prey struggle as it transfers force to stiffer, support line flagelliform fibers. In large orb webs, switchback capture thread turns are placed at the bottom of the web before a continuous capture spiral progresses from the web’s periphery to its interior. To determine if the properties of capture thread droplets change during web spinning, we characterized droplet and glycoprotein volumes and material properties from the bottom, top, middle, and inner regions of webs. Both droplet and glycoprotein volume decreased during web construction, but there was a progressive increase in the glycoprotein’s Young’s modulus and toughness. Increases in the percentage of droplet aqueous material indicated that these increases in material properties are not due to reduced glycoprotein viscosity resulting from lower droplet hygroscopicity. Instead, they may result from changes in aqueous layer compounds that condition the glycoprotein. A 6-fold difference in glycoprotein toughness and a 70-fold difference in Young’s modulus across a web documents the phenotypic plasticity of this natural adhesive and its potential to inspire new materials.
... intercepted, and their ultimate recognition by the spider are equally, or perhaps more, important actions Tarakanova and Buehler, 2012;Blamires et al., 2018). Prey retention is driven by the adhesiveness of the gluey silks of the spiral threads (Craig, 1987;Tarakanova and Buehler, 2012;Blamires et al., 2018), which are dynamically affected by the interplay between temperature and humidity (Stellwagen et al., 2014;Opell et al., 2017), as well as UV radiation (Stellwagen et al., 2015(Stellwagen et al., , 2016. It is well known now that at high temperature and humidity, water infiltrates the gluey silks of spider orb webs and mobilizes the glycoproteins in the glues (Sahni et al., 2011;Stellwagen et al., 2014). ...
Lay Summary.
How climate change impacts animal extended phenotypes (EPs) is poorly understood. We modelled how temperature and humidity affects the ability of spider webs to intercept prey. We found humidity had negative effects at the extremes. Temperature, however, likely interacts with humidity to affect web tension and prey retention.
... In previous studies, it has been reported that electron spin resonance was used to study the influence of UV light, including UVA, UVB, and UVC, on spider draglines [134,135]. It has also been reported that UVA mechanically corroborated the diurnal spider draglines of Nc. spider [136] in spite of the fact that its impact on energy of mechanical breaking is not explored. ...
... Silkworm silk fiber has been widely used as a biomaterial [4,[141][142][143]. Osaki et al [135,136] have made observations on spider silk Nephila clavata (Nc) using spin electron resonance. The results show that Nc is more resistant to UV radiation compared with the Bombyx mori silk fiber. ...
... A growing number of studies on the properties and performance of orb-weaver prey capture thread have revealed details about this natural adhesive system and how it responds to environmental humidity (Figure 1d), temperature, ultraviolet light, and insect surface texture (Opell Clouse & Andrews, 2018;Opell, Jain, et al., 2018;Opell & Schwend, 2007;Stellwagen, Opell, & Clouse, 2015Stellwagen, Opell, & Short, 2014). Humidity has a pronounced effect on glue droplet adhesion, and interspecific differences in this response have been attributed to natural selection that optimizes thread performance to the humidity of each species' habitat (Amarpuri, Zhang, et al., 2015). ...
... Plexiglas desiccator cabinets again served as chambers where 37%, 55%, and 72% RH was established ( We monitored temperature using a thermometer suspended 1 cm below the top of each chamber and maintained at 23°C to standardize our observations to both the previous insect retention study (Opell et al., 2017) and studies of capture thread droplet properties (Opell, Clouse, & Andrews, 2018;Opell et al., 2013;Stellwagen, Opell, & Clouse, 2015Stellwagen et al., 2014). To 37% RH and 72% RH chambers, we added a 22 × 15 cm aluminum heat sink that extended 11 cm into the top of the chamber and served to dissipate the heat added by the dehumidifier and humidifier, respectively. ...
An orb web's adhesive capture spiral is responsible for prey retention. This thread is formed of regularly spaced glue droplets supported by two flagelliform axial lines. Each glue droplet features a glycoprotein adhesive core covered by a hygroscopic aqueous layer, which also covers axial lines between the droplets, making the entire thread responsive to environmental humidity.
We characterized the effect of relative humidity (RH) on ability of Argiope aurantia and Argiope trifasciata thread arrays to retain houseflies and characterize the effect of humidity on their droplet properties. Using these data and those of Araneus marmoreus from a previous study, we then develop a regression model that correlated glycoprotein and flagelliform fiber properties with prey retention time. The model selection process included newly determined, humidity‐specific Young's modulus and toughness values for the three species' glycoproteins.
Argiope aurantia droplets are more hygroscopic than A. trifasciata droplets, causing the glycoprotein within A. aurantia droplets to become oversaturated at RH greater than 55% RH and their extension to decrease, whereas A. trifasciata droplet performance increases to 72% RH. This difference is reflected in species' prey retention times, with that of A. aurantia peaking at 55% RH and that of A. trifasciata at 72% RH.
Fly retention time was explained by a regression model of five variables: glue droplet distribution, flagelliform fiber work of extension, glycoprotein volume, glycoprotein thickness, and glycoprotein Young's modulus.
The material properties of both glycoprotein and flagelliform fibers appear to be phylogenetically constrained, whereas natural selection can more freely act on the amount of each material invested in a thread and on components of the thread's aqueous layer. Thus, it becomes easier to understand how natural selection can tune the performance of viscous capture threads by directing small changes in these components.
... This allows the glue to adhere to fast-moving insects at interception, and retain insects while a spider travels to and subdues them. Orb weaver glue responds instantly to humidity, which changes droplet volume, influences the performance of the glue, and is functionally optimized for a spider's habitat (Opell et al. 2011;Sahni et al. 2011a;Stellwagen et al. 2014Stellwagen et al. , 2015. ...
An individual orb weaving spider can spin up to seven different types of silk, each with unique functions and material properties. The capture spiral silk of classic two-dimensional aerial orb webs is coated with an amorphous glue that functions to retain prey that get caught in a web. This unique modified silk is partially comprised of spidroins (spider fibroins) encoded by two members of the silk gene family. The glue differs from solid silk fibers as it is a viscoelastic, amorphic, wet material that is responsive to environmental conditions. Most spidroins are encoded by extremely large, highly repetitive genes that cannot be sequenced using short read technology alone, as the repetitive regions are longer than read length. We sequenced for the first time the complete genomic Aggregate Spidroin 1 (AgSp1) and Aggregate Spidroin 2 (AgSp2) glue genes of orb weaving spider Argiope trifasciata using error-prone long reads to scaffold for high accuracy short reads. The massive coding sequences are 42,270 bp (AgSp1) and 20,526 bp (AgSp2) in length, the largest silk genes currently described. The majority of the predicted amino acid sequence of AgSp1 consists of two similar but distinct motifs that are repeated ∼40 times each, while AgSp2 contains ∼48 repetitions of an AgSp1-similar motif, interspersed by regions high in glutamine. Comparisons of AgSp repetitive motifs from orb web and cobweb spiders show regions of strict conservation followed by striking diversification. Glues from these two spider families have evolved contrasting material properties in adhesion (stickiness), extensibility (stretchiness), and elasticity (the ability of the material to resume its native shape), which we link to mechanisms established for related silk genes in the same family. Full-length aggregate spidroin sequences from diverse species with differing material characteristics will provide insights for designing tunable bio-inspired adhesives for a variety of unique purposes.
... Orb weavers produce glue optimized for their habitat's humidity, for example the glue of species from drier habitats becomes over-lubricated when exposed to higher humidity, while glue from species occupying wetter habitats becomes too viscous in drier conditions. Moreover, temperature and ultraviolet exposure also influence performance optima (Stellwagen et al., 2014(Stellwagen et al., , 2015. ...
The aggregate gland glycoprotein glue coating the prey-capture threads of orb weaving and cobweb weaving spider webs is comprised of silk protein spidroins (spider fibroins) encoded by two members of the silk gene family. It functions to retain prey that make contact with the web, but differs from solid silk fibers as it is a viscoelastic, amorphic, wet adhesive that is responsive to environmental conditions. Most spidroins are extremely large, highly repetitive genes that are impossible to sequence using only short-read technology. We sequenced for the first time the complete genomic Aggregate Spidroin 1 (AgSp1) and Aggregate Spidroin 2 (AgSp2) glue genes of Argiope trifasciata by using error-prone long reads to scaffold for high accuracy short reads. The massive coding sequences are 42,270 bp (AgSp1) and 20,526 bp (AgSp2) in length, the largest silk genes currently described. The majority of the predicted amino acid sequence of AgSp1 consists of two similar but distinct motifs that are repeated ~40 times each, while AgSp2 contains ~48 repetitions of an AgSp1-similar motif, interspersed by regions high in glutamine. Comparisons of AgSp repetitive motifs from orb web and cobweb spiders show regions of strict conservation followed by striking diversification. Glues from these two spider families have evolved contrasting material properties in adhesion, extensibility, and elasticity, which we link to mechanisms established for related silk genes in the same family. Full-length aggregate spidroin sequences from diverse species with differing material characteristics will provide insights for designing tunable bio-inspired adhesives for a variety of unique purposes.
... Temperature and ultraviolet light influence viscous thread properties and performance (Stellwagen et al., 2015b(Stellwagen et al., , 2016(Stellwagen et al., , 2014, although humidity has the greatest and most universal effect. As RH decreases during daylight hours, temperature increases, mediating the decrease in absolute humidity and reducing glycoprotein viscosity. ...
Orb-weaving spiders use adhesive threads to delay the escape of insects from their webs until the spiders can locate and subdue the insects. These viscous threads are spun as paired flagelliform axial fibers coated by a cylinder of solution derived from the aggregate glands. As low molecular mass compounds (LMMCs) in the aggregate solution attract atmospheric moisture, the enlarging cylinder becomes unstable and divides into droplets. Within each droplet an adhesive glycoprotein core condenses. The plasticity and axial line extensibility of the glycoproteins are maintained by hygroscopic LMMCs. These compounds cause droplet volume to track changes in humidity and glycoprotein viscosity to vary approximately 1000-fold over the course of a day. Natural selection has tuned the performance of glycoprotein cores to the humidity of a species' foraging environment by altering the composition of its LMMCs. Thus, species from low-humidity habits have more hygroscopic threads than those from humid forests. However, at their respective foraging humidities, these species' glycoproteins have remarkably similar viscosities, ensuring optimal droplet adhesion by balancing glycoprotein adhesion and cohesion. Optimal viscosity is also essential for integrating the adhesion force of multiple droplets. As force is transferred to a thread's support line, extending droplets draw it into a parabolic configuration, implementing a suspension bridge mechanism that sums the adhesive force generated over the thread span. Thus, viscous capture threads extend an orb spider's phenotype as a highly integrated complex of large proteins and small molecules that function as a self-assembling, highly tuned, environmentally responsive, adhesive biomaterial. Understanding the synergistic role of chemistry and design in spider adhesives, particularly the ability to stick in wet conditions, provides insight in designing synthetic adhesives for biomedical applications.
... Previous studies have found that the mechanical properties of glue droplets are largely dependent on the contact state and ambient conditions, e.g. humidity [29][30][31][32], temperature [33] and UV radiation [34]. Better spreading of the glue on a substrate surface enhances adhesion [35] and higher humidity is propitious to enlarge the ultimate extensibility of glue droplets [30]. ...
It is well known that capture silk, the main sticky component of the orb web of a spider, plays an important role in the spider's ability to capture prey via adhesion. However, the detailed mechanism with which the spider achieves its unparalleled high-adhesion performance remains elusive. In this work, we combine experiments and theoretical analysis to investigate the adhesion mechanisms of spider silk. In addition to the widely recognized adhesion effect of the sticky glue, we reveal a synergistic enhancement mechanism due to the elasticity of silk fibres. A balance between silk stiffness, strength and glue stickiness is crucial to endow the silk with superior adhesion, as well as outstanding energy absorption capacity and structural robustness. The revealed mechanisms deepen our understanding of the working principles of spider silk and suggest guidelines for biomimetic designs of spider-inspired adhesion and capture devices.
