Researchers spin spider webs as tool to sample biodiversity

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For millions of years, spider webs have been really, really good at catching things. Now, researchers have begun to cotton on to how they might use this ability to their own ends. A proof of concept study published last week in the journal PLoS ONE finds that it’s possible to extract DNA from spider webs and identify the species from which the genetic material came, suggesting a possible new tool for studying spiders and their prey.

Researchers collected cobwebs made by black widow spiders in an exhibit at the Potawatomi Zoo in South Bend, Indiana. They extracted DNA from the webs with a procedure similar to the one used on shed reptile skin. Then they compared the DNA found on the webs to known sequences, called DNA “barcodes,” that are characteristic of different species of organisms.

The researchers identified southern black widow (Latrodectus mactans) DNA from all three of the webs sampled. They also found DNA from house crickets (Acheta domesticus) that zookeepers had fed to the spiders.

They even identified both spider and cricket DNA from a fourth web – this one belonging to a western black widow (L. hesperus) – collected 88 days after the spider’s death and removal from the zoo exhibit. This suggests that environmental DNA can persist on spider webs for long periods of time.

The webs in the study were collected from controlled indoor environments, and future studies will have to determine whether field-collected webs from other habitats also reliably yield DNA. In addition, the DNA analysis method used in the study depends on having access to good DNA barcode libraries, which are still under construction for some groups.

Still, the findings open up the possibility of using DNA collected from spider webs in a broad array of environmental studies, the researchers say. Webs are abundant and easy to find, while spiders themselves can be elusive. Sampling DNA from webs could help scientists survey spider biodiversity without bothering or harming the animals themselves. (In the case of spiders, studying DNA is an especially good strategy because they are notoriously difficult to identify based on their appearance.)

Web DNA could help scientists monitor the spread of invasive spiders, identify the presence of venomous pests, and map the distribution and assess genetic diversity of rare or declining species.

The ability to extract prey DNA from webs could also aid in dietary studies of spiders, reveal the structure of arthropod communities, and enable population monitoring of specific insect species.

Nor is DNA the limit: Previous studies have found that spider webs also collect pollen, fungal spores, and pesticides from their surroundings. Viewed in a certain light, a spider web begins to look like a shimmering microcosm of its environment.

“Sticky spider webs are natural DNA samplers, trapping nearby insects and other things blowing in the wind,” says Charles Cong Xu, the study’s first author. “We see potential for broad environmental monitoring because spiders build webs in so many places.” – Sarah DeWeerdt | December 1, 2015

Source: Xu C.C.Y. et al. “Spider web DNA: A new spin on noninvasive genetics of predator and prey.” PLoS ONE DOI: 10.1371/journal.pone.0142503

Header image: Southern black widow spider (Latrodectus mactans) is with its prey house cricket (Acheta domesticus) trapped in spider web. Credit: Scott Camazine.