The effects of wind on trap structural and material properties of a sit-and-wait predator

Numerous terrestrial invertebrates use secretions produced by themselves to build prey traps. Potentially, the structural as well as material properties of such constructions will reflect adaptations to wind disturbances, but most relevant studies only focus on trap structural characteristics. In this study, we examined how wind disturbances affected the structural and material properties of prey traps constructed by a sit-and-wait Araneae predator. We first compared web structures and major ampullate (MA) silk properties of 2 Cyclosa spider species inhabiting seashores and forests to see whether these properties reflected the habitat-specific wind disturbances these spiders experienced. The MA silks of the seashore-dwelling Cyclosa mulmeinensis were significantly thicker and contained higher percentage of glycine and lower glutamine. Congruent with such amino acid variation pattern were higher ultimate tension and breaking energy of C. mulmeinensis MA silks. However, despite that this species' silks were relatively glycine rich and glutamine poor, they also showed greater extensibility. Compared with webs built by Cyclosa ginnaga, those built by C. mulmeinensis were composed of fewer drag-reducing silk threads but were stiffer. In a laboratory manipulation, MA silk amino acid composition and diameter did not differ between C. mulmeinensis receiving different levels of wind. However, those receiving persistent wind disturbances built smaller webs composed of fewer but stronger MA silks to reduce drag and prevent the web from damage. Orb web spiders inhabiting areas with different levels of wind disturbances exhibit variation and plasticity in structural and material properties of prey traps. Furthermore, the silk property plasticity does not have to involve alterations of amino acid composition. Copyright 2009, Oxford University Press.