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Rise of the Orb-Weaver Spiders

Aaron Pomerantz

Spiders! They’re creatures you’re almost certain to see in the Peruvian Amazon, whether you like it or not.

Spiders have been around for hundreds of millions of years and have adapted to almost every corner of the earth. As predators, they have developed a very unique strategy of producing webs made of silk to catch prey and one particular group, called the orb-weavers, create spiral round-shaped webs to ensnare their flying victims.

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A spined Micrathena spider, belonging to family Araneidae


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An orb-weaver in the genus Nephila, family Araneidae

The Deinopoidea (the cribellate orb weavers) and the Araneoidea (the viscid silk orb weavers) are two groups of spiders that make geometrically similar orb webs and for a long time scientists thought that orb weavers were one distinct lineage. However, a recent study out of Harvard proves that this is false: the orb weavers are in fact nonmonophyletic, meaning they do not share a single origin.

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The net-casting spider, a cribellate orb-weaver in the family Deinopidae

The researchers utilized thousands of genes from various spider species and conducted a phylogenetic analysis, which looks at the evolutionary relationships among groups of organisms. Here’s how it works in a nutshell:

  • They used next-generation sequencing, a technology which allows scientists to rapidly sequence the genetic material of an organism.
  • For each spider specimen, the messenger RNA (mRNA) was extracted, complementary DNA (cDNA) libraries were constructed, and samples were run using an Illumina platform, thus sequencing and generating a huge amount of genetic data.
  • The data was then used to construct a phylogenetic tree, which represents the evolutionary relationships among spiders.
  • After all the hard work, the researchers produced the most comprehensive analysis to date for investigating spider evolution.

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How could you not love that spidey-face?

The controversy over a single or a convergent origin of the orb web goes back to at least the 1880s. Research, primarily based on behavioral and morphological data, have supported a single origin of the orb web, but this new study clearly shows that Deinopoidea is not closely related to Araneoidea.

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Orb-weaver (Araneidae) enjoying a freshly caught grasshopper

Thus, orb webs appear to have evolved convergently in Araneoidea and Deinopoidea. Either that, or the orb web is an ancestral phenomenon and has been lost in all lineages except Araneoidea and Deinopidea. This is very cool research, and only time will tell what new insights scientists come to gain on arachnid evolution.

Citation: Fernandez R, Hormiga G, Giribet G. 2014. Phylogenomic analysis of spiders reveals nonmonophyly of orb weavers. Current Biology 24:1772-1777



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