Mechanical performance of spider silk is robust to nutrient-mediated changes in protein composition.

Spider major ampullate (MA) silk is sought after as a biomimetic because of its high strength and extensibility. While the secondary structures of MA silk proteins (spidroins) influences silk mechanics, structural variations induced by spinning processes have additional effects. Silk properties may be induced by spiders feeding on diets that vary in certain nutrients, thus providing researchers an opportunity to assess the interplay between spidroin chemistry and spinning processes on the performance of MA silk. Here, we determined the relative influence of spidroin expression and spinning processes on MA silk mechanics when Nephila pilipes were fed solutions with or without protein. We found that spidroin expression differed across treatments but that its influence on mechanics was minimal. Mechanical tests of supercontracted fibers and X-ray diffraction analyses revealed that increased alignment in the amorphous region and to a lesser extent in the crystalline region led to increased fiber strength and extensibility in spiders on protein rich diets.