Title page for ETD etd-02012003-095259


Type of Document Master's Thesis
Author Campbell-Hawthorn, Anya
Author's Email Address anhawth1@vt.edu
URN etd-02012003-095259
Title An investigation of the stickinness mechanism and the role of nodes in cribellar spider capture thread
Degree Master of Science
Department Biology
Advisory Committee
Advisor Name Title
Opell, Brent D. Committee Chair
Sible, Jill C. Committee Member
Webster, Francis Committee Member
Keywords
  • evolution of capture thread
  • hygriscopic adhesion
  • van der Waals
  • spider silk
  • cribellar thread
Date of Defense 2002-10-04
Availability unrestricted
Abstract
Sticky prey capture threads are produced by many members of the spider Infraorder Araneomorphae. Cribellar threads are plesiomorphic for this clade, and adhesive threads are apomorphic. The surface of cribellar thread is formed of thousands of fine fibrils. Basal araneomorphs produce cylindrical fibrils, whereas more derived members produce fibrils with nodes. Cribellar fibrils snag and hold rough surfaces, but other forces are required to explain their adherence to smooth surfaces. Threads of Hypochilus pococki (Hypochilidae) that are formed of non-noded fibrils hold to a smooth acetate surface with the same force under low and high humidities. In contrast, threads of Hyptiotes cavatus and Uloborus glomosus (Uloboridae) that are formed of noded fibrils hold with greater forces to the same surface at intermediate and high humidities. Threads spun by eight species representing seven genera and four families with noded fibrils absorb water, while that of two families, represented by one species each with smooth fibrils, repel water, indicating increase hygroscopisity associated with the presence of nodes. Additionally, equations describing van der Waals and hygroscopic forces can predict the observed stickiness of these threads. This model supports the hypothesis that van der Waals forces allow non-noded cribellar fibrils to adhere to smooth surfaces, whereas noded fibrils employ van der Waals forces at low humidities and add hygroscopic forces at higher humidities. Thus, there appear to have been two major events in the evolution of spider prey capture thread: the addition of hydrophilic nodes to the fibrils of cribellar threads and the replacement of cribellar fibrils by glycoprotein glue.
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