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Todd A Blackledge
Faculty
University of Akron
Biology
Akron, OH USA
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| Silk biomechanics and energy absorption in spider orb webs |
| Author(s) |
Andrew Sensenig, Sean Kelly, Kimberly Lorentz, Todd A Blackledge |
| Info |
Talk category:
Behavior |
| Abstract |
The kinetic energy of flying insect prey represents a formidable challenge for orb weaving spiders who rely on their webs to first absorb the kinetic energy of flight and then to adhere to insects. While spider silks are renowned for their exceptional material properties, the micron-sized diameters of threads also results in a low Reynolds number and hence viscous interactions with air. This led to the aerodynamic dissipation hypothesis that suggests that drag of silk threads moving through air plays a dominant role in how orb webs stop flying insects. However, evidence for the aerodynamic dissipation hypothesis is derived primarily from studies of single silk threads from Araneus. Here, we present a comprehensive study of how orb webs deform under prey impact for several species of Araneidae. We calculate energy dissipation budgets using data derived from high speed images of web deformation in conjunction with material tensile testing. Our findings emphasize the importance of the intrinsic work performed by silk molecules within radial threads, and downplay the role of aerodynamic dissipation and capture spiral deformations in many webs. |
| Molecular and biomechanical insights into the parallel origin of orb-like webs in spiders |
| Author(s) |
Ingi Agnarsson, Dakota Piorkowski, Matja Gregori, Matja Kuntner, Todd A Blackledge |
| Info |
Poster category:
Systematics |
| Abstract |
The evolutionary origin of the spider orb web in Orbiculaiae was accompanied by new spinning behaviors and significant changes in the material properties of silk. In particular, the major ampullate silk that forms the backbones of most webs is stronger and stiffer among orb-weaving spiders, possibly facilitating the capture of flying insect prey. However, the little known Fecenia also constructs a two-dimensional aerial web that is strikingly similar to an orb web. Here, we first test the evolutionary affinity of the pseudo orb versus genuine orb webs and then compare the material properties of their silks. We sample two Fecenia and one Psechrus species (both in Psechridae) and sequence partial fragments of mitochondrial (16S, COI) and nuclear (18S, 28S, H3, wingless) markers, adding these data to the published orbicularian and RTA matrices to infer their phylogenetic affinities using Bayesian inference. We also perform tensile tests on the radii from both types of webs to compare their material properties in a broader evolutionary context. |
| Adaptive foraging in orb-weaving spiders: predicting adaptive changes in web structure in response to change in hunger level using a computer simulation model. |
| Author(s) |
Samuel C Evans, Todd A Blackledge |
| Info |
Talk category:
Behavior |
| Abstract |
Orb-weaving spiders rebuild their webs daily using a finite volume of silk, which scales positively with spider body mass, as does the energy absorption potential of the silk threads. The “large, rare prey hypothesis” dictates that spiders build webs that maximize the probability of securing large-but-rarely-encountered prey, which are essential to the spider’s reproductive success. However, this likely involves concentrating the allotment of silk in a web of smaller planar area, which lowers the prey-web encounter rate. Therefore, there is an apparent trade-off between prey-web encounter rate and web performance. Spiders that have not recently secured a sizeable meal, and are therefore close to starving, might benefit from a “bet-hedging” strategy of increasing web size to increase prey-web encounter rate, while spiders that are further away from starvation benefit more from gambling with a smaller web that is more effective at securing a large prey item. Therefore, we hypothesize that spiders can adaptively alter web size in response to change in proximity to starvation (“hunger level”). To generate predictions based on this hypothesis, we have constructed a computer simulation model. Prey capture is a three-step process: the web must 1) contact, 2) stop, and 3) retain the prey item. Our model calculates a probability of success in each of these three steps; the product of these probabilities is the probability of prey capture. This process is repeated over thirty days, or until the spider starves, and the growth rates and survival frequencies are compared among spiders using different strategies. Model predictions and planned empirical tests will be discussed. |
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