Collaborative Research: Integrating molecular and material evolution of spider aqueous glues

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The spectacular diversity of spiders and their role as key predators across the globe can largely be attributed to their innovative uses of silk. For instance, a golden orb-web spider or a black widow can spin six different types of dry fibers and a wet adhesive silk. The wet adhesive silks made by these spiders and their relatives (the megadiverse superfamily Araneoidea) afford them greater prey retention for a lower material cost than the dry prey capture silk spun by other spider groups. Furthermore, these silk glues achieve adhesiveness in a wide variety of environments, including extreme humidity conditions that challenge commercial glues. A multidisciplinary team from three institutions will investigate how variation in adhesive protein components relates to variation in the glue's material properties. The wet adhesive silks of the 18 target species have significant variation in adhesiveness, material efficiency, and response to humidity. Thus, the discovery of constituent proteins will allow design of environmentally friendly glues with tailored properties. Furthermore, web-building spiders offer many opportunities for science educators to integrate biology, chemistry, physics, and mathematics as they engage their students in the natural world. The team of investigators will mentor undergraduate and Master's students, as well as incorporate the research into undergraduate course curricula. Additionally, team members will offer science enrichment activities at rural Virginia public elementary schools, run workshops for middle and high school science teachers, and mentor New York City high school students to complete original research projects.The evolutionary diversity of spider aqueous glues offers a unique opportunity compared to other bioadhesives to determine how molecular building blocks contribute to different aspects of adhesion. By integrating transcriptomics, proteomics, and biomechanics within a phylogenetic framework, the proposed experiments will pinpoint protein characteristics that co-evolve with interfacial adhesion, intra-glue cohesion, and humidity responsiveness. Objective 1 identifies shifts in gene expression associated with the evolution of wet adhesive silk by profiling transcriptional diversity in each of the silk gland types of 5 divergent araneoid species and 3 outgroup taxa. It also investigates evolution of expression levels in the adhesive-producing silk glands of an additional 13 species that build different web types and forage under divergent humidity levels. Objective 2 identifies and quantitates the proteins that compose adhesive silks of all 18 species, as well as their post-translational modifications. Objective 3 measures wet adhesive silk material properties for the same 18 species at different humidities. These integrated experiments will contribute to understanding the origin and molecular underpinnings of a key innovation. Specifically, they will determine the degree to which gene expression shifts and new genes were required to make a novel type of silk. The proposed work will track evolutionary rates in glue protein characteristics, including post-translational modifications, which is currently poorly understood. Finally, glue material property measurements will test the hypothesis that humidity responsiveness of spider glue droplets has evolved for optimal performance at the humidity in which a spider species typically forages.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.