Web building and silk properties functionally covary among species of wolf spider

Spider silk tensile performance does not correlate with web use

Spider silk is amongst the toughest materials produced by living systems, but its tensile performance varies considerably between species. Despite the extensive sampling of the material properties and composition of dragline silk, the understanding of why some silks performs better than others is still limited. Here, I adopted a phylogenetic comparative approach to reanalyze structural and mechanical data from the Silkome database and the literature across 164 species to (a) provide an extended model of silk property evolution, (b) test for correlations between structural and mechanical properties, and (c) to test if silk tensile performance differs between web-building and nonweb-building species. Unlike the common notion that orb-weavers have evolved the best-performing silks, outstanding tensile properties were found both in and outside the araneoid clade. Phylogenetic linear models indicated that the mechanical and structural properties of spider draglines poorly correlate, but silk strength and toughness correlated better with birefringence (an indicator of the material anisotropy) than crystallinity. Furthermore, in contrast to previous ideas, silk tensile performance did not differ between ecological guilds. These findings indicate multiple unknown pathways toward the evolution of spider silk tensile super-performance, calling for better integration of nonorb-weaving spiders in spider silk studies.

Meta-analysis reveals materiomic relationships in major ampullate silk across the spider phylogeny

Spider major ampullate (MA) silk, with its combination of strength and extensibility, outperforms any synthetic equivalents. There is thus much interest in understanding its underlying materiome. While the expression of the different silk proteins (spidroins) appears an integral component of silk performance, our understanding of the nature of the relationship between the spidroins, their constituent amino acids and MA silk mechanics is ambiguous. To provide clarity on these relationships across spider species, we performed a meta-analysis using phylogenetic comparative methods. These showed that glycine and proline, both of which are indicators of differential spidroin expression, had effects on MA silk mechanics across the phylogeny. We also found serine to correlate with silk mechanics, probably via its presence within the carboxyl and amino-terminal domains of the spidroins. From our analyses, we concluded that the spidroin expression shifts across the phylogeny from predominantly MaSp1 in the MA silks of ancestral spiders to predominantly MaSp2 in the more derived spiders' silks. This trend was accompanied by an enhanced ultimate strain and decreased Young's modulus in the silks. Our meta-analysis enabled us to decipher between real and apparent influences on MA silk properties, providing significant insights into spider silk and web coevolution and enhancing our capacity to create spider silk-like materials.

Silk physico-chemical variability and mechanical robustness facilitates intercontinental invasibility of a spider

There are substantive problems associated with invasive species, including threats to endemic organisms and biodiversity. Understanding the mechanisms driving invasions is thus critical. Variable extended phenotypes may enable animals to invade into novel environments. We explored here the proposition that silk variability is a facilitator of invasive success for the highly invasive Australian house spider, Badumna longinqua. We compared the physico-chemical and mechanical properties and underlying gene expressions of its major ampullate (MA) silk between a native Sydney population and an invasive counterpart from Montevideo, Uruguay. We found that while differential gene expressions might explain the differences in silk amino acid compositions and protein nanostructures, we did not find any significant differences in silk mechanical properties across the populations. Our results accordingly suggest that B. longinqua’s silk remains functionally robust despite underlying physico-chemical and genetic variability as the spider expands its range across continents. They also imply that a combination of silk physico-chemical plasticity combined with mechanical robustness might contribute more broadly to spider invasibilities.