Argiope (Orb weaver) aggregate glue protein composition

Using proteomics, we documented the glue composition in two congeners that live in different environments, Argiope argentata (dry southwest US) and A. trifasciata (humid southeast US). The viscoelastic protein cores of A. argentata droplets comprised a smaller portion of droplet volume than did those of A. trifasciata and, as humidity increased, incorporated a smaller percentage of absorbed water. Argiope argentata core protein was many times stiffer and tougher than A. trifasciata protein. Each species’ glue included ~30 aggregate-expressed proteins, most of which (24 and 23, respectively) were homologous between the two species. However, the relative contribution and number of gene family members of each homologous group differed. For instance, the aggregate spidroins (AgSp1 and AgSp2) accounted for nearly half of the detected glue composition in A. argentata, but only 38% in A. trifasciata. Additionally, AgSp1, which has highly negatively charged regions, was ~2X as abundant as the positively charged AgSp2 in A. argentata but ~3X as abundant in A. trifasciata. As another example, A. argentata glue included 11 members of a newly discovered cysteine-rich gene family, versus 5 in A. trifasciata. The ability to selectively express different glue protein genes and/or to extrude their products at different rates provides a faster mechanism to evolve material properties than sequence evolution alone.