Untangling Spiders' Evolutionary Web

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"Taxonomy was more art than science and was theoretically misguided," said Jonathan Coddington, another colleague of Wheeler and a curator of arachnida and myriapoda at the Smithsonian's National Museum of Natural History in Washington, D.C.

For the past three decades, scientists have favored a new approach that compares specific morphological, behavioral, and genetic characteristics among species, taking advantage of computer power to tease out evolutionary links.

Hundreds of characteristics for each species are fed into a computer matrix that compares these with equivalent features from thousands of other species. Only recently have there been powerful enough computers to support such calculations.

Spider Silk

Museums contain archive arachnid collections but new specimens need to be collected so that the DNA can be extracted for analysis. Specialists are traveling the world to seek about 500 species of spiders, a sampling of most of the 108 spider families.

Jason Bond, an evolutionary biologist at East Carolina University in Greenville, North Carolina, specializes in trapdoor and funnel-web spiders, and tarantulas. The last two summers, Bond has hunted spiders in Australia and South Africa. With a small shovel and pick he digs up the trapdoor spider burrows, which vary in length from one inch to two feet (2.5 to 61 centimeters).

In Australia, Bond collected 32 types of trapdoor spiders, including a close relative, the funnel-web—the most lethal specimen to humans, but not fully understood.

"The selection of spiders represents diversity as well as focusing on particular species whose evolutionary history is controversial," Bond said.

The Spider Tree of Life is important to science—and to the silk industry, among others. Weight for weight, spider silk is stronger than steel and any manmade fiber like Kevlar.

"The two silk genes currently being used commercially are from two spiders that are not even particularly good at silk production," Coddington pointed out.

"If you want to produce silk using spider genes then you want to choose the spider whose life depends on the strongest silk—as it stands we don't know how far spiders have taken silk development." The Tree of Life could help determine the best silk-spinners.



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