Evolution of supercontraction in spider silk: structure-function relationship from tarantulas to orb-weavers

Area of Science:

• Biomaterials Science
• Evolutionary Biology
• Zoology

Background:

• Spider silk is a high-performance biomaterial with potential applications in synthetic production.
• Certain spider silks exhibit 'supercontraction' when exposed to water, shrinking significantly in length.
• The molecular mechanisms and functional significance of supercontraction remain largely unelucidated.

Purpose of the Study:

• To investigate the evolutionary origins and molecular basis of supercontraction in spider silk.
• To test the hypothesis that GPGXX motifs drive supercontraction and its functional role in web architecture and material properties.

Main Methods:

• Supercontraction of silk fibers was measured across 28 diverse spider taxa, from tarantulas to orb-weavers.
• Silk protein composition, specifically GPGXX motif ratios, was analyzed in relation to supercontraction.
• Evolutionary patterns of supercontraction were compared with spider phylogeny and web architecture.

Main Results:

• Silk from all tested species supercontracted, with the notable exception of most tarantulas, indicating an ancient evolutionary origin.
• Supercontraction evolved at least with the origin of the Araneomorphae infraorder, over 200 million years ago.
• The degree of fiber shrinkage in unrestrained supercontracting silk positively correlated with high ratios of GPGXX motifs, particularly in Orbiculariae spiders.

Conclusions:

• Supercontraction is a widespread trait in spider silk, driven by the rearrangement of GPGXX motifs.
• This mechanism allows spiders to tailor silk properties for diverse ecological functions, such as preventing orb-web sagging in wet conditions.
• The findings support the hypothesis that GPGXX motif rearrangement is the cause of supercontraction and highlight its adaptive significance.