Evol Ecol Res 3: 507-519 (2001) Full PDF if your library subscribes.
Changes in the mechanical properties of capture threads and the evolution of modern orb-weaving spiders
Brent D. Opell1
and Jason E. Bond2
1Department of Biology, Virginia Tech., Blacksburg, VA 24061 and 2Department of Zoology – Insect Division, Field Museum of Natural History, Roosevelt Road at Lake Shore Drive, Chicago, IL 60605, USA
Author to whom all correspondence should be addressed.
The capture threads of spider orb-webs retain prey and contribute to a web’s ability to absorb the forces generated when prey strike the web. Primitive orb-webs produced by the Deinopoidea clade are horizontally oriented and contain dry, fuzzy (cribellar) capture thread, whereas modern orb-webs constructed by the Araneoidea clade are vertically oriented and contain viscous adhesive threads. Independent contrast analyses find no relationships between spider mass or features of web architecture and the tensile strengths, Young’s moduli and breaking energies of capture threads. Cribellar and adhesive threads have similar breaking energies, but the manner in which they resist breaking differs. The tensile strengths and Young’s moduli of adhesive threads are smaller than those of cribellar threads, rendering adhesive threads weaker, but better equipped to dissipate force by stretching. This mode of absorbing force is advantageous for vertical orb-webs, which typically intercept faster flying prey than horizontal orb-webs. The greater extensibility of adhesive capture thread allows an orb-web to dissipate energy locally as capture threads stretch while transferring force and also enhances the web’s overall extensibility, allowing it to flex and dissipate force through air resistance.
Keywords: adhesive thread, breaking energy, character evolution, cribellar thread, tensile strength, Young’s modulus.
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