But what happened afterward to produce the explosion of spider diversity seen now has been mysterious. Those abdomens were still segmented, not fused as in today's spiders. By 300 million years ago, fossils show, eight-legged creatures with spiderlike mouth parts, primitive silk glands, and stumpy abdomens had emerged.
"It's changed the kinds of questions people can ask."īased mainly on fossil evidence and specimens preserved in amber, biologists concluded long ago that spiders descended from a many-legged, scorpionlike ancestor that by 380 million years ago had a long tail but looked quite spiderlike and may even have had silk glands. "Genomics has impacted nearly everything," says Jason Bond, who studies spiders at Auburn University in Alabama. The analyses are highlighting the tangled paths of spider evolution, bringing into focus the complexities of spider silk and venom, and suggesting molecular-based ways to study these animals' behaviors.
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Researchers have sequenced full genomes of three species-the golden orb-weaver, the African social velvet spider, and the common house spider-and have done more limited genetic and protein studies on many others. Lately, however, studies of genes and proteins are opening a new era of spider biology. Until recently, arachnologists trying to unravel how spiders' vast range of adaptations arose built family trees based on morphology and behavior. The same goes for venom, another universal spider attribute-each species makes a different concoction of up to 1000 different compounds. This material, used for capturing prey, rappelling from high places, and building egg cases and dwellings, is itself fantastically diverse, its makeup varying from species to species. Spiders' universal ability to make silk helps explain their global success-an estimated 90,000 species thrive on every continent except Antarctica. By night, the female bolas swings a silken line with a sticky ball at its end while emitting the scent of a female moth to lure and nab male moths.Īmong spiders, "Every group has a weird story," says Hannah Wood, a spider researcher at the Smithsonian Institution National Museum of Natural History (NMNH) in Washington, D.C. Bolas spiders, named for the South American weapon made of cord and weights, specialize in mimicry. Showy peacock spiders, in contrast, flaunt rainbow-colored abdomens to attract mates, while their outsized eyes discern fine detail and color-the better to see both strutting mates and unsuspecting prey.
Throughout the tropics these eight-legged monsters hang from twigs, an expandable silk net stretched between their front legs so they can cast it, lightning-fast, over their victims. Take the reclusive ogre-faced spider, with its large fangs and bulging, oversized middle eyes. For a display of nature's diabolical inventiveness, it's hard to beat spiders.
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