BELTR�N, Jennie L.; BLACKLEDGE, Todd A.; SUMMERS, Adam P.; HAYASHI, Cheryl Y.; University of California-Irvine; University of California-Riverside; University of California-Irvine; University of California-Riverside: The effect of spider size and amino acid composition on the mechanical properties of dragline silk

Many studies have explored the material properties, composition, and genetics of the dragline silk spun by the spider, Nephila clavipes. Nephila‘s dragline silk is primarily composed of two proteins, major ampullate spidroins 1 and 2. Both proteins contain large amounts of alanine and glycine, but vary dramatically in their proline content. Specifically, spidroin 1 has no proline while spidroin 2 has 15% proline. Because each protein has been hypothesized to contribute different mechanical properties to the dragline, silks with different concentrations of the two proteins might vary in their physical characteristics. Furthermore, it has been suggested that the composition of dragline silk changes as spiders develop. To investigate whether the material and biochemical properties of dragline silk change as spiders mature, we measured the tensile strength, extensibility, and Young’s modulus of dragline silk from different sized Nephila spiders. Spools of silk were collected for amino acid composition analyses to estimate the relative amounts of the two spidroins. The spider’s weight and right femur length were used to quantify body size. Thus, we were able to correlate the properties of dragline silk with the spider size and biochemical data. We found that the size of the spider did not affect the mechanical properties of its dragline silk. However, some mechanical properties are affected by the biochemical composition of the silk.