Tuesday, 22 July 2014

Spider gene study reveals tangled evolution

Arachnid family tree suggests that many spider species evolved away from web-weaving.
21 July 2014

There’s more than one way to catch a fly. Spider webs look like the perfect trap for ensnaring insects, but a spider ‘tree of life’ based on hundreds of genes suggests many spiders jettisoned the web in favour of other ways of capturing prey. The new studies overturn decades-old dogma, by showing that spiders that weave orb-shaped webs are not all close kin, with some species more related to species that catch prey differently.

“They are awesome, spider webs — they’re just not the pinnacle of spider evolution that we thought,” says Jason Bond, an evolutionary biologist at Auburn University in Alabama, whose team determined the evolutionary relationship of spiders by analysing more than 300 genes in 33 families1. The paper and a similar study from an independent team2 are both published this week in Current Biology.

Scientists have so far named around 45,000 spider species, grouped into more than 100 families. The spiders that spin orb-shaped webs belong to two main families ­— araneoids, such as garden spiders, and the more obscure deinopoids, which include ogre-faced spiders. The two groups spin webs out of chemically distinct silks — araneoids weave a sticky fibre that is made more efficiently than the dryer webs of deinopoids. But because the groups weave webs similarly, arachnologists have long put the two together on the spider family tree in a group called orbicularians.

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