Spider silk is a biomaterial that combines high strength and extensibility. Because of these exceptional material properties, silk could be used for many applications. However, before we can mass-produce spider silk analogs for these applications, we need to better understand the relation between silk molecular structure and its properties. Furthermore, the whole range of properties that can be achieved by silks may not have been gauged yet, as most studies focus on a few selected species.
The first part of my research focused on silk plasticity. I found that common house spiders (Achaearanea tepidariorum) change their silk properties in function of their prey type (cricket or pillbug). Silk properties also differ between different regions of the cobweb spun by a common house spider. However, silk properties did not differ for other species (black widows and bridge spiders). Major ampullate silk plasticity increased during spider evolution. Silk plasticity may be mediated by a valve present in the spinning duct of Orbicularia, which allows them to apply shear forces during forcible silking and control their speed during falls. Silk plasticity may have been selected for as spiders make more diverse uses of their major ampullate silk.
The second part of my research dealt with supercontraction. Supercontraction refers to the shrinking of silk exposed to high humidities. Several hypotheses on its mechanisms and functions have been proposed, but seldom tested. By measuring supercontraction in many different spider species, with various silk composition, web type and silk uses, I tested three of these hypotheses. GPGXX amino acid motif are likely involved in supercontraction. Furthermore, supercontraction probably allows spiders to better tailor their silk properties, but, contrary to an early idea, it may not help protect webs from water drops. Supercontraction may affect how whole webs function too. Supercontracted webs were found to absorb more kinetic energy and deform more when hit by a projectile (mimicking a flying prey). Thus, another potential function of supercontraction is to improve web performance.
To conclude, my research shed light on various aspects of silk material properties by taking an evolutionary approach. This approach may be expanded further in order to better understand silk evolution and estimate the range of silk properties. This study also helps better understand how silk properties and web architecture interact within spider webs.