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Orb weavers produce webs that trap prey using a capture spiral formed of regularly spaced glue droplets supported by protein fibers. Each droplet consists of an outer aqueous layer and an adhesive, viscoelastic glycoprotein core. Organic and inorganic compounds in the aqueous layer make droplets hygroscopic and cause droplet features to change with environmental humidity. When droplets contact a surface, they adhere and extend as an insect struggles. Thus, a droplet’s extensibility is as important for prey capture as its adhesion. Cursory observations show that droplets can adhere, extend, and pull off from a surface several times, a process called cycling. Our study cycled individual droplets of four species—Argiope aurantia, Neoscona crucifera, Verrucosa arenata, and Larinioides cornutus. Droplets were subjected to 40 cycles at two humidities to determine how humidity affected droplet performance. We hypothesized that droplets would continue to perform, but that performance would decrease. Droplet performance was characterized by filament length and force on droplets at pull-off, aqueous volume, and glycoprotein volume. As hypothesized, cycling decreased performance, notably extensibility and aqueous volume. However, humidity did not impact the response to cycling. In a natural context, droplets are not subjected to extensive cycling, but reusability is advantageous for orb-weaving spiders. Moreover, the ability to cycle, combined with their environmental responsiveness, allows us to characterize orb weaver droplets as smart materials for the first time.
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Linking properties of an orb‐weaving spider's capture thread glycoprotein adhesive and flagelliform fiber components to prey retention time
Abstract 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 ofArgiope aurantiaandArgiope trifasciatathread arrays to retain houseflies and characterize the effect of humidity on their droplet properties. Using these data and those ofAraneus marmoreusfrom 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.Argiopeaurantiadroplets are more hygroscopic thanA. trifasciatadroplets, causing the glycoprotein withinA. aurantiadroplets to become oversaturated at RH greater than 55% RH and their extension to decrease, whereasA. trifasciatadroplet performance increases to 72% RH. This difference is reflected in species' prey retention times, with that ofA. aurantiapeaking at 55% RH and that ofA. trifasciataat 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.
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- Award ID(s):
- 1755028
- PAR ID:
- 10459692
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 9
- Issue:
- 17
- ISSN:
- 2045-7758
- Page Range / eLocation ID:
- p. 9841-9854
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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