The origin of orbs

Spectacular web designs trace back to a single spider origin

Spiders responsible for the majestic feats of architecture called orb webs may have evolutionarily diverged from a single weaver. Though modern-day spiders spin silken snares of many different shapes and sizes, arachnids belonging to the Orbiculariae taxon — the orb weavers — can most likely trace their ancestry to a web designer of the prehistoric kind, an international team of researchers reports November 2 in Proceedings of the Royal Society B.

The traditional orb web (shown above with a spider from the family Araneidae) is characterized by radial spokes of spider silk connected by concentric circles of the same sticky thread. This pattern may have been the original design used by prehistoric orb weaving ancestors. Gustavo Hormiga

To learn more about the evolution of orb weavers and paint a clearer picture of their web-decorated family tree, the scientists examined molecular differences in six genes across 300 species of spiders. The number of differences in the DNA of related species corresponds with how much time has transpired since they diverged from a common ancestor.

Based on this molecular data, ancestors of orb-weaving spiders first crafted their sticky traps around 200 million years ago, suggest zoologist Dimitar Dimitrov, of the University of Copenhagen and George Washington University in Washington, D.C., and colleagues. Although the orb weavers rapidly evolved new web materials (such as stickier, more viscous silk) and new web designs (such as sheet and cobwebs) to more effectively capture insect prey, the various snares probably derive from a single original design plan.  

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