Table 3.

Hypothesized relationships between molecular structure, mechanical performance, and ecological use of silks spun by Argiope argentata

SilkMolecular elementsMechanical performanceEcological function
Major ampullateComposition: GA and poly(A) motifs, short repeats of GPGXn motifs1,2High tensile strength, low extensibility, high loss tangent, exhibits super contraction when wetted, higher hysteresisDraglines, primary dry structural elements of most capture webs
2° structure: β-sheet crystals oriented along fiber axis embedded in amorphous matrix3,4
TubuliformComposition: A and S rich, long and complex repeats lacking in subrepeat motifs5,6High modulus, low strength, very little stiffening after fiber yield, consistently low storage modulus, loss tangent is relatively constant after fiber yield, thick diameterInner flocculent silk of egg sacs
2° structure: β-sheets twist parallel to fiber orientation embedded in amorphous matrix3,7,8,9
Minor ampullateComposition: GA motifs lack poly(A) motifs1High modulus and extensibility, moderate tensile strength and toughnessTemporary spiral of orb, sometimes added to draglines
2° structure: β-sheet crystals oriented along fiber axis embedded in amorphous matrix9
AciniformComposition: G, A and S rich, long, complex repeats lacking in subrepeat motifs10High modulus, extensibility and toughness, high storage modulus, multi-strand sheet of fine fibersPrey wrapping, stabilimentum web decorations, outer layer of egg sacs
2° structure: uncharacterized
Capture spiralComposition: core fiber (flagelliform silk gland) coated with glycoprotenin glue, core fiber has long repeats of GPGXn motifs11Extremely extensible and resilient, highly compliant, glue-coated wet fiberSticky spiral of ecribellate orb webs
2° structure: lacks β-sheet, subrepeats fold into molecular `nanosprings', plasticized fiber12,13,14,15,
  • Amino acids are indicated by one-letter abbreviations: A, alanine; G, glycine; P, proline; S, serine; X, glycine or other amino acid. 1(Gatesy et al., 2001), 2(Xu and Lewis, 1990), 3(Parkhe et al., 1997), 4(Thiel et al., 1997), 5(Garb and Hayashi, 2005), 6(Tian and Lewis, 2005), 7(Barghout et al., 2001), 8(Barghout et al., 1999), 9(Dicko et al., 2004), 10(Hayashi et al., 2004), 11(Hayashi and Lewis, 2000), 12(Gosline et al., 1984), 13(Hayashi and Lewis, 1998), 14(Hayashi and Lewis, 2001), 15(Vollrath and Edmonds, 1989).