Do spider silk biomaterials evolve as quickly as behaviors during adaptive radiations in Hawai'i?

Methods

Summary

Webs from Tetragnatha will be collected in four islands of the Hawaiian archipelago. Capture spiral threads and major ampullate (dragline) threads will be collected directly from each web. Dragline will also be reeled directly from the spiders’ spinnerets under control conditions for both lineages of Tetragnatha (orb weavers and cursorial non-orb weavers). Silk mechanical properties will be study using a Nano Bionix test system (Agilent Technologies, Oak Ridge, TN, USA, Figure 1) to compare dragline and capture spirals across orb-weavers, as well as dragline properties between orb-weavers and cursorial non-orb weavers. Since silk performance is determined in part by chemical composition, amino acid composition will be determined using High Performance Liquid Chromatography. Solution-State NMR will measure salt composition of glue droplets in capture spirals, which helps determine glue stickiness.

Figure 1. Force-Extension curve obtained from mechanical testing of materials. The Nano Bionix test system will allow us to obtain measurements of tensile strength, extensibility and toughness of spider silk.

Together, these data will test how silk material properties evolved during the rapid behavioral radiations of endemic Hawaiian spiders, and how these properties enhance web functions. A better understanding of how silks interact with web structures during prey capture, how and why silk properties vary at individual and interspecific levels, and what selective pressures drive the evolution of silk properties will reveal new possibilities for the application of silk analogues.

Challenges

Weather is not something we can control once we are out in the field. Hawaiian Tetragnatha build webs during very humid conditions, and at night. Rain is very common in this type of environment necessary for humid conditions but not for finding orb-webs. Sufficient time at each island (2 weeks) will give a good time-frame to get good perfect weather nights.