HAYASHI, C.Y.*; SWANSON, B.O.; BLACKLEDGE, T.A.; SUMMERS, A.P.; Univ. of California, Riverside; Pacific University, Oregon; Univ. of Akron, Ohio; Univ. of California, Irvine: Evolution of the Material Properties of Spider Dragline Silk

The evolution of biological materials is poorly understood, but is critical for understanding biodiversity. For example, the performance, and hence evolution of spiders is dependent on the silks they spin throughout their lives. The material properties of these fibers, such as the strength, toughness, extensibility, and stiffness, affect a myriad of ecologically important functions. Here, we examine the evolution of dragline silk material properties across a phylogenetically diverse sample of 21 species of spiders. Material properties such as strength and toughness can vary by more than four-fold across species. Further, the associations between different properties are complex with some traits evolving independently of one another (e.g. strength and extensibility) and others demonstrating correlated evolution (e.g. extensibility and toughness). Material properties also have different degrees of phylogenetic signal, with similarities between closely related species in stiffness and strength, but very little similarity in extensibility and toughness. The overall picture that emerges is complex, with a mosaic pattern of trait evolution that produces a diverse set of materials across spider species.