Tough threads, ballistic webs and bungee-jumps: evolutionary biomechanics of spider extended phenotypes

Jonas Wolff

Spider silk is among the toughest known materials, enabling spiders to construct multi-functional architectures with a minimum of material investment. Spiders use these architectures (threads, webs, retreats and egg cases) as extended interfaces with their environment, which may impressively enhance their predatory, defensive and locomotor capabilities. Spiders typically produce multiple types of silk secretions in differentiated glandular systems, that are connected to spinnerets – leg-like appendages equipped with various muscles that enable fine-scale movements to form a multitude of materials. In this talk I will demonstrate how spiders via evolutionary novelties in the secretion and behavioural processing of silk fibres repeatedly overcame trade-offs in the mechanical properties of biological materials.

I will discuss how the evolution of novel silk-aided behaviours may change the selective landscape of silk toughness, and how novel spinning behaviours enhanced the elasticity of silk threads. Further, I will show how spiders may use silk architectures for power amplification surpassing the limitations of muscle performance by three orders of magnitude, to subdue hazardous prey. These examples show how evolutionary novelties in behavioural, morphological and physiological traits can each expand the range of extended phenotype functions, resulting in an enormous flexibility.