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Spiderwebs could offer a snapshot of an ecosystem, study shows


The rich tapestry of life on Earth is fraying, due in large part to habitat loss and climate change. Researchers are racing to track this global decline in biodiversity, to understand its consequences, and perhaps to counteract it through conservation efforts. Now there may be a new tool for monitoring animals - spider webs. Here's science reporter Ari Daniel.

ARI DANIEL, BYLINE: For a long time, if you wanted to know which animals were in a particular place, you'd hike or climb into their habitat and then wait to see or hear them. But that approach can have its drawbacks, particularly if you're trying to reach remote places or if you're trapping animals.

JOSH NEWTON: That puts stress on the animals. And especially if you're, I suppose, looking for rare and endangered species, that's not a great thing, not something you want to do.

DANIEL: Josh Newton is a Ph.D. student in genetic biodiversity at Curtin University in Australia. In recent years, scientists have turned to a different way of monitoring biodiversity - DNA. Morten Allentoft, an evolutionary biologist and one of Newton's advisers, says you can think of DNA as ecology's version of "Everything Everywhere All At Once."

MORTEN ALLENTOFT: Every species that exists in a given environment, in a given ecosystem, they may be dying, decomposing, urinating, defecating, breathing, whatever. And all these processes facilitates the shedding of cells into the environment, and all cells have DNA in them.

DANIEL: This is known as environmental DNA because it's DNA from creatures just lying around in the environment. Researchers have swabbed it off of leaves and flowers, filtered it from water, pulled it out of the air and even picked it up in the guts of dung beetles. One day, as Allentoft was walking around a lake in his home of Perth, he noticed heaps of giant webs in the trees made by golden orb-weaving spiders.

ALLENTOFT: I've been told in my biology days, you know, that spider webs are sticky. So it's one of those things where you can see they're messy, they're dirty. And I was thinking to myself, maybe these spider webs, big passive air filters, they sit there for days or weeks, months even. They may very well be capturing the DNA that are floating around.

DANIEL: Previous work showed that webs are good sources of insect DNA, including what spiders are gorging on. But Allentoft and Newton wanted to see whether these webs were also trapping DNA from vertebrate animals blown there by the wind or deposited by insects. So Newton drove to a woodland sanctuary about 30 miles outside of Perth and collected spiderwebs from the branches and bushes.

NEWTON: We just got a plastic stick. It's almost - if you look at "Shrek" where Princess Fiona's collecting spiderweb fairy floss for Shrek, it's very similar to that process. (Laughter) You just grab a stick and wrap it around.

DANIEL: Were there ever spiders in the webs?

NEWTON: We just gently ushered them off the web. None of them were collected.

ALLENTOFT: So when we say this is noninvasive, well, the spiders may not really think that, but - (laughter).

DANIEL: Back in the lab, they amplified the teensy amounts of DNA from the webs and, whammo, animals from Down Under.

ALLENTOFT: It was wonderful. We could see these kangaroos, wallabies.

DANIEL: In addition to 13 species of birds, the motorbike frog and the snake-eyed skink. But to really confirm that the webs were picking up DNA from local vertebrate animals, they collected webs at the Perth Zoo. And there they found DNA from giraffes, elephants, rhinos, orangutans, lemurs, meerkats. In other words, the technique worked and represents a new way of tracking animal biodiversity and alerting us when we should intervene to conserve it. The findings are published in the journal iScience.

ELIZABETH CLARE: I think it's clever and cute. It's a nice, non-invasive way of sampling for terrestrial vertebrates.

DANIEL: Elizabeth Clare is a molecular ecologist at York University in Toronto. She wasn't involved in the study.

CLARE: There are thousands of papers studying the movement of DNA through water and very few on land. And so we really need more explorations like this to narrow down how far the material travels, how it accumulates and how long these signals last.

DANIEL: So that we can query this worldwide web for information on the status and future of the animals all around us.

For NPR News, I'm Ari Daniel.

(SOUNDBITE OF FLYING LOTUS' "FF4") Transcript provided by NPR, Copyright NPR.

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Ari Daniel
Ari Daniel is a reporter for NPR's Science desk where he covers global health and development.