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Spiders produce up to seven types of silk. One of the most commonly produced silks, called dragline, is used as a safety line by most kinds of spiders. Gravid female orb weavers have large abdomens and are heavy enough that a hard impact could be fatal. The worst case scenario would be a fall with a preformed length of silk and no additional silk spooled by the spider. Tests of the material properties show that the dragline produced by the adult orb weaver Araneus diadematus would indeed break during such a fall. To explain this apparent discrepancy between material property and function, I am measuring silk spooling rates as well as friction forces associated with spooling. Pictures! One of my hobbies is photography, with spiders as the favorite subject. Go here to see some of my photos of first instar A. diadematus being persued by a hungry ant. |
Ph.D. student Ken Savage, B.Sc.
| Spider dragline silk is known for its remarkable properties of high strength and exceptional toughness, and therefore the structural aspects which bring about these properties are of great interest to biopolymer researchers. Measurements of the mechanical properties and birefringence, an index of molecular order, were performed on dry dragline fibers from two orb-weaving spiders, Nephila clavipes and Araneus diadematus. In addition, these measurements were repeated on draglines that were submersed in water and allowed to supercontract. Dry N. clavipes dragline exhibits a higher birefringence and is stiffer and less extensible than the dragline silk produced by A. diadematus. Also, the N.clavipes dragline is not as well plasticized by water, showing a smaller relative decrease in stiffness and molecular order (birefringence) upon supercontraction. The fibroin genes expressed in the major ampulate (MA) gland of N. clavipes encodes significantly less proline than the fibroin genes of A. diadematus. The lower expression of proline in the dragline silk from N. clavipes would allow the protein network to form a more ordered non-periodic lattice crystal structure, thus explaining greater stiffness and increased molecular order. |
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