One of the three small sections of amber that contains the fossilised spider web.
Credit: Science
SYDNEY, 23 June 2006 - The stereotypical spider's web shape may have a single origin dating back to the late Jurassic period, according to new research.
Evidence published in Thursday's issue of the U.S. journal Science, said two groups of orb-web spinners called Deinopoidea and Araneoidea, share key silk proteins, with fossil evidence suggesting that the ancestor of the two spider groups probably existed around 136 million years ago.
The two groups were previously thought to have developed their web-spinning technique separately but Jessica Garb, lead author and post-doctoral researcher at the University of California, Riverside said her work "does not support a double origin for the orb web".
Garb and colleagues examined silk proteins from deinopoid spiders, a group previously unstudied, investigating the genetics of key silk proteins that create orb webs, including web components like spokes and sticky capture threads of the orb's spiral.
Most spiders are able to spin numerous different types of silk and each type has different functions. "These mechanical differences are related to the proper functioning of the web for capturing flying insects," said Garb. "The same spider will also use a different type of silk to make its egg case and another silk for wrapping prey."
Because araneoids produce glue droplets and deinopoids use a different type of silk fibre for their capture threads, scientists believed the orb web evolved independently for these spider groups instead of inheriting it from a common ancestor. But Garb said her team found the different silks are constructed with the same set of genes.
Her findings were corroborated by evidence from a site in Spain of a web preserved in amber. Entangled with insects and dating to 110 million years ago, the find is the oldest known example of a web with trapped insects, according to co-author of a separate Science paper, David Grimaldi of the American Museum of Natural History.
The preserved parts suggest an orb web design because of the insects found in the ancient web - a mite, a wasp leg and a beetle. "Their size and diversity are precisely what one would expect to see in modern webs," said Grimaldi.
