Irvine, Calif., Sept. 27, 2006 -- Researchers have found for the first time that tarantulas can produce silk from their feet as well as their spinnerets, a discovery with profound implications for why spiders began to spin silk in the first place.
Adam Summers, a UC Irvine professor of ecology and evolutionary biology, was among the team of scientists who made the discovery using zebra tarantulas from Costa Rica. The team found that the tarantulas secrete silk from spigots on their legs, allowing them to better cling to surfaces. Until now, spiders were only known to spin silk from spinnerets located on their abdomen and to use the silk to form webs for protection and capturing prey rather than for locomotion.
The findings are published in the current issue of Nature.
"If we find that other spiders in addition to these tarantulas have the ability to secrete silk from their feet, this could represent a major change in our evolutionary hypothesis regarding spider silk," Summers said. "It could mean that silk production actually originated in the feet to increase traction, with the diversity of spinneret silk evolving later."
The researchers placed tarantulas on a vertical glass surface. Though ground dwelling, these spiders can normally hang on to vertical surfaces by using thousands of spatulate hairs and small claws. However, the scientists noticed that when the spider started to slip down the surface, it produced silk from all four pairs of legs, allowing it to adhere to the glass for more than 20 minutes. The silk secretions were clearly visible on the glass. Using scanning electron microscopy, the scientists also were able to see the openings on the legs that resemble the silk-producing spigots on spider abdominal spinnerets.
The next step, according to Summers, is to investigate whether the silk produced by the feet is the same as that produced by the spinneret. Many spiders can produce seven different kinds of silk. Scientists will look at the genes involved in silk production from the feet, compare them to the gene family that leads to spinneret silk production, and be able to better determine whether silk was originally used for traction, or whether that was a secondary usage that came later.
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Collaborating on the study were Stanislav Gorb of the Max Planck Institute for Metals Research in Germany; Senta Niederegger of the Friedrich Schiller University of Jena in Germany; Cheryl Hayashi of UC Riverside; Walter Vötsch of the Max Planck Institute for Developmental Biology in Germany; and Paul Walther of the University of Ulm in Germany.
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