Abstract
Spider major ampullate gland silks (MAS) vary greatly in material properties among species but, this variation is shown here to be confined to evolutionary shifts along a single universal performance trajectory. This reveals an underlying design principle that is maintained across large changes in both spider ecology and silk chemistry. Persistence of this design principle becomes apparent after the material properties are defined relative to the true alignment parameter, which describes the orientation and stretching of the protein chains in the silk fiber. Our results show that the mechanical behavior of all Entelegynae major ampullate silk fibers, under any conditions, are described by this single parameter that connects the sequential action of three deformation micromechanisms during stretching: stressing of protein-protein hydrogen bonds, rotation of the β-nanocrystals and growth of the ordered fraction. Conservation of these traits for over 230 million years is an indication of the optimal design of the material and gives valuable clues for the production of biomimetic counterparts based on major ampullate spider silk.
Highlights
Major ampullate (MA) silk plays a conspicuous role in the construction of webs and safety lines for most of the world’s 45000 species of spiders[1]
These values are consistent with the model since the increase in the initial slope with increasing α T is explained as the result of the combined effect of a –presumably– constant contribution from hydrogen bonds and the rising stiffness of the protein chains, represented by the slope of the maximum supercontracted (MS) fiber tested in water
The predicting ability of α *T is illustrated in Fig. 2C, where the true stress-true strain curves of MAS fibers spun by different species and with different values of α T are shown to concur in their post-yield behaviour
Summary
Major ampullate (MA) silk plays a conspicuous role in the construction of webs and safety lines for most of the world’s 45000 species of spiders[1]. Comparable variability is seen when comparing fibers spun by different species despite carefully controlling the environmental conditions under which spinning takes place, and even measuring the forces exerted on the fiber during the silking process[4,6,7,8] This variability is supposed to originate at different levels ranging from variation among species in the sequences of silk genes[9] and differential gene expression[10], to physiological tuning by individual spiders during spinning[8] and might play a significant role in the evolutionary success of the group. The whole range of stress-strain curves of MAS spun by a single species can be classified with the definition of the alignment parameter, α , as illustrated in Fig. 1B, and the usage of this parameter allows even the comparison of fibers spun by different species[14,15]
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