Disentangling the effect of web building behavior and silk material properties on orb web functionality

The efficacy of spider orb webs depends on the functional integration of architecture and material properties. Here, we investigated species-specific correlations between orb web architecture and mechanical properties of major ampullate silk (i.e., radii silk) across several orb-weaving spider species. To disentangle the effect that manipulation during the spinning process and the composition of major ampullate silk have on this relationship, the silks were tested in two states. In the native state, the spider tailors the mechanical properties of the radii silks to their intended function within the constraints provided by the silk's composition. In contrast, in the freely supercontracted state after exposure to high humidity, much behavioral manipulation is removed, revealing the silk's intrinsic material properties conveyed by its primary structure. While the properties of freely supercontracted silk are not directly relevant to web function, combining this information with native silk data generated a more complete picture of the underlying processes of silk adaptation. While the number of spiral turns was positively correlated with native silk extensibility, supercontracted silk strength and toughness were positively correlated with the number of radial threads in a web. These results suggested a concerted use of intrinsic and behaviorally manipulated silk properties and web architecture to maximize web performance. Thereby, different silk properties are adjusted via alternative routes, possibly due to the specific energetic cost associated with each adjustment.