Spiders weaved their nets 230 million years ago

DNA comparison confirms the common origin of all network forms

A true spiderweb (Araneidae) in its typical network of straight threads with fine glue droplets. © Gustavo Hormiga
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More than 230 million years ago, spiders spanned their first cycle networks - at a time when the first dinosaurs were developing. The ancestors of all today's spiders lived 60 million years earlier than previously believed by fossil finds. An international research team has found this out on the basis of comparative genetic analyzes. The results also show that all techniques used by today's spiders developed from a common archetype of the spider web, the scientists report in the journal "Proceedings of the Royal Society B".

The spiders now use their spinnability very differently to catch their prey: spiders and their relatives use fine glue droplets to make their nets sticky. Cave spiders and other real spiders weave their nets without glue. Instead, they produce a very fine, entangled spider silk, in which catch the prey insects.

Throwing nets and glue balls

Some spiders today no longer build traditional wheel nets, but use litter nets or a glue ball on a monofilament to catch their prey. Hunting spiders even hunt completely without a net and use their spinnability only for egg cocoons and as a security line.

"Our findings point to a common origin of all these network forms, " ​​write study director Gustavo Hormiga of George Washington University in Washington, DC, and his colleagues. However, in the course of their evolution, the spiders would have developed many of today's seemingly similar mesh construction techniques independently of each other.

The ancestors of this colorful colored spiderweb (Arkys sp.) From Australia spanned their nets 230 million years ago. © Gustavo Hormiga

No pure robber booty race

The new pedigree of the spiders and their network forms also provides clues as to why the spiders developed such diverse network designs. So far, it has always been assumed that the nets became more sophisticated the more different prey insects there were. "According to this theory, spider webs evolved in a kind of evolutionary armament race between predator and prey, " the researchers write. However, the new results indicated that the history of spider web forms is more complex than previously thought. display

"Environmental change, competition from other spiders, and the conquest of new niches are also likely to play an important role, " say Hormiga and his colleagues. For example, the once complex forests of the Carboniferous period were greatly reduced by the mass extinction 250 million years ago. Until the end of the Triassic and early Jurassic, these habitats and their inhabitants developed to new heights. With them, the spiders could have found numerous new niches, the researchers say.

This spider of the genus Deinopis no longer weaves a classic wheel net, but uses a throw net to see here between the front legs to catch their prey. Gustavo Hormiga

Gene markers of 192 spider species compared

For their study, the scientists had reconstructed the pedigree of the web spiders with the help of the genome of living spiders today. They compared the structure and distribution of several genetic markers in 291 spider species in 50 families. Using this method, they were able to trace the origins of the first spiders back to the Middle Triassic 230 million years ago.

By contrast, the oldest known fossil finds from web spiders date back to the middle Jurassic, around 170 million years ago. "According to our findings, most of the spider families known today had already developed at this time, " say the researchers. (Proceedings of the Royal Society B, 2011; doi: 10.1098 / rspb.2011.2011)

(Proceedings of the Royal Society B / dapd, 02.11.2011 - NPO)