Scientists discover that properties of glue in Orb weaver spiders evolve at a faster pace than their glue genes.

Spiders that do not weave good silk do not eat. The silk spiders produce to create their webs is key to their survival – but spiders live in many different places that require well-tuned webs for local success. Scientists have now studied the glue that makes Germanic weaving spiders’ webs sticky to understand how the materials’ properties differ in different conditions.

Nadia Ayoub of the University of Washington and Lee University, co-author of the study published in the journal Frontiers in ecology and evolution. “Spider silk fibers and gums are a great model for answering such questions because they are primarily composed of proteins and proteins that are encoded by genes.”

“Spider silks and adhesives have enormous biomimetic potential,” added Dr. Brent Opel of Virginia Tech, co-author. “Spiders make adhesives with remarkable properties that will have applications in industry, medicine and more.”

tangled in spider webs

Each thread of a spider’s web contributes to a fleeing orb catching food. The web has a rigid framework that absorbs the impact of the prey, which is then trapped by sticky lines for the spider to manipulate. These sticky lines are made by water-based papain synthesized in the kidney glands. The glue absorbs water from the atmosphere and must be optimized to achieve the best local humidity adhesion results. But there are many species of Germanic weaver spiders that live in different environments, which means that their slime must adapt to different levels of humidity.

To understand how spider gum adapts, Ayoub and her colleagues focused on two species, Argiope argentata, that live in dry environments. and Argiope trifasciata, which lives in moist environments. The team collected webs from A. trifasciata in the wild and had A. argentata spiders build webs in the lab. To ensure that these webs were equivalent to webs in the wild, the scientists fed the spiders a diet comparable to their usual prey and compared the size of the glue droplets to wild controls to ensure that humidity in the laboratory did not affect the properties of the droplets. . Then they analyzed the proteins in the glue and the droplet material properties.

A difficult situation

The team found that the droplets of A. argentata spiders are smaller than those of A. trifasciata and absorb less water as local humidity increases. They also had smaller protein cores, occupying a smaller percentage of the droplet’s volume, and absorbing less water from the atmosphere. The rigidity of the glue droplets of both spider species depended on the rigidity of the protein core of the droplets, and the rigidity of the protein core of Argentata decreased with higher humidity. The glue droplets of Filamentum argentata were more spaced apart and generally stickier.

The scientists also analyzed the proteins in the glue droplets to understand how these differences in the material properties of the proteins might emerge. Although the proteins they found were similar, they appeared in different proportions, and the gum of A. argentata contained protein products of four genes that did not appear in the gum of A. trifasciata. These additional proteins and the more balanced ratio of AgSp1 and AgSp2 proteins may explain both the greater toughness of this mucilage and its lower ability to absorb water.

“Despite the significant differences in material properties, the two species share most of their protein components,” said Oppel. “The sequences of these proteins are also similar between species, but the relative abundance of individual proteins varies. Modifying the ratios of proteins is likely to be a rapid mechanism for adjusting the material properties of biological adhesives.”

“This study only examined two species, so our proposed relationships between proteins and material properties are limited,” Ayoub cautioned. “However, we are in the process of documenting protein components and material properties for a variety of species, which will allow more power to discover the mechanisms of how proteins effect material properties.”