Fig 1.
Viscous prey capture threads and their droplets.
A. Argiope aurantia female depositing a capture thread. B. A suspended A. aurantia viscous droplet, showing paired flagelliform axial fibers, as magnified by the droplet’s curved surface, C. A flattened N. crucifera droplet showing a glycoprotein core attached to axial fibers and surrounded by aqueous material. D. An extended N. crucifera droplet, which has deflected its support line.
Fig 2.
Video screen captures of a V. arenata capture thread being progressively pulled (bottom to top) from a 2mm wide contact plate.
Force from the thread’s extending droplets is summed by its deflected axial line. In the top frame a droplet near the strand’s center has released from the plate, introducing an instability that will initiate adhesive failure. Thread release is more typically initiated when peripheral droplets release. Middle and top figures from Opell et al., 2018.
Fig 3.
Components of the droplet extension system.
1. An isolated droplet suspended between supports with the probe’s tip positioned and ready to contact droplet. 2. Microscope slide sampler within the glass-covered humidity and temperature controlled temperature chamber resting on the microscope’s mechanical stage. 3. Stepping motor used to activate the mechanical stage’s X manipulator, which pushes the stage to the left of the image. 5. Stationary device that holds the probe stationary as the stage is moved. 6. Adjustable plate with a port for the probe to pass through, enabling the probe tip to be aligned with a thread droplet before the probe is stabilized. 7. Intake and outlet ports used to draw dehumidified air or room air into the observation chamber. 8. Hygrometer probe used to monitor chamber humidity and thermistor probe for controlling chamber humidity. 8. Peltier heating and cooling block, which maintains chamber temperature. Modified after Opell, Karinshak, and Sigler, 2011.
Fig 4.
Values and formulas used to characterize glycoprotein performance and material properties.
Fig 5.
Progressive extension of an individual A. aurantia droplet, showing the formation of aqueous layer droplets on the glycoprotein filament.
Fig 6.
The effects of humidity and extension on the ratio of a glycoprotein filament’s circumference to the area of its aqueous layer.
As surface tension is related to circumference, an increase in this index favors the formation of aqueous droplets like those shown in Fig 5.
Fig 7.
Stress-strain curves and Young’s modulus values derived from Phase 1 and Phase 2 region of stress-strain curves.
Histogram error bars are ± 1 standard error. Grand means and standard errors are given for each species’ values and the P values of Wilcoxon Tests of the effect of RH on E. Letters denote the ranking of values that were significantly affected by RH, as determined by Wilcoxon Each Pairs Tests.
Table 1.
Percent droplet extension ranges used for computing Young’s modulus (E) and percent droplet extension ranges summed to determine toughness (T) values for Phase 1 and Phase 2 of droplet extension.
Fig 8.
Toughness values derived from Phase 1 and Phase 2 region of stress-strain curves.
Histogram error bars are ± 1 standard error. Grand means and standard errors are given for each species’ values and the P values of Wilcoxon Tests of the effect of RH. Letters denote the ranking of values that were significantly affected by RH, as determined by Wilcoxon Each Pairs Tests.
Table 2.
Inter-specific comparisons of Young’s modulus values.
Table 3.
Inter-specific comparisons of toughness values.
Table 4.
Intra-specific comparisons of Phase 1 and Phase 2 Young’s modulus values.
Table 5.
Intra-specific comparisons of Phase 1 and Phase 2 toughness values.
Fig 9.
Comparison of 55% RH Phase 1 Young’s modulus and toughness of glycoprotein from this study with flagelliform, and major ampullate fiber values measured in the range of 50% RH (Sensenig et al., 2010).
Young’s modulus values are plotted and described on the Y-axis. Toughness values appear beside these points. Error bars are ± 1 standard error. Lines connecting the glycoprotein, flagelliform, and major ampullate values are provided to make it easier to interpret the figure and are not regression lines.