Spiderwebs can be used as air filters capturing environmental DNA from terrestrial vertebrates, according to scientists.
Rob Stothard/Getty Images
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Rob Stothard/Getty Images
The diverse array of life on Earth is diminishing, largely due to human-induced habitat destruction and climate change. As more species vanish, researchers are working to monitor this global decline in biodiversity to comprehend its impact and counteract it through conservation efforts. These endeavors depend on precise animal monitoring, which can be challenging, time-consuming, and expensive. Now, in a recent study published in the journal iScience, researchers present evidence for a new affordable, non-invasive tool for animal monitoring: spiderwebs. Here’s how traditional monitoring has worked: If one wanted to determine the presence of animals in a specific area, they would trek or climb into their habitat and wait to observe or hear them. However, this approach has its limitations. “If you’re frequently conducting visual surveys in a harsh environment,” says Josh Newton, a Ph.D. student in genetic biodiversity at Curtin University in Perth, Australia, “that can be quite challenging.” Another drawback of traditional monitoring is the potential trapping of animals. “This causes stress to the animals,” Newton explains. “Especially when you’re searching for a rare and endangered species, it’s not ideal — it’s not something you want to do.”
DNA is ubiquitous In recent years, scientists have turned to a different approach for biodiversity monitoring, using environmental DNA, or eDNA, which refers to the DNA of various organisms present in the environment. This concept can be likened to “everything everywhere all at once” in ecology. “Every species that exists in a specific environment, within a specific ecosystem — they may be dying, decomposing, urinating, defecating, breathing, etc.,” says Morten Allentoft, an evolutionary biologist at Curtin University. These processes “result in the shedding of cells into the environment, and all cells contain DNA.” Researchers have collected eDNA from leaves, flowers, water, air, dung beetles’ bodies, and leeches’ blood meals. One day, while strolling around Bibra Lake in Perth, Allentoft observed large webs crafted by golden orb weaving spiders in the trees. “I’ve been informed in my biology days that spiderwebs are sticky,” he remarks with a smile. “They are messy, they are dirty. And I was thinking to myself, ‘Maybe these spiderwebs are big passive air filters. They sit there for days or weeks — even months. They could very well be capturing the DNA that is floating around.'” Previous studies have shown that spiderwebs are effective sources of insect DNA, including the prey of spiders. However, Allentoft and Newton aimed to ascertain whether the webs were also capturing DNA from vertebrate animals, possibly carried there by the wind or deposited by insects.
Kangaroos, wallabies, and more Newton visited the Karakamia Wildlife Sanctuary, a woodland approximately 30 miles outside Perth, and gathered spiderwebs from the branches and bushes. “If you look at Shrek where Princess Fiona’s collecting spiderweb fairy floss for Shrek, it’s very similar to that process,” Newton describes. “Just grab a stick and wrap it around.” No spiders were harmed or captured, even though their webs were dismantled. “We just gently ushered them off the web,” Newton says. The spiders’ reaction to this approach is uncertain. “So when we say this is noninvasive,” Allentoft adds with a grin, “well, the spiders may not really think that.” In the laboratory, Newton amplified the small amounts of DNA from the webs, which were found to contain genetic material from various animals in the region. “It was marvelous,” says Allentoft. “We could see these kangaroos and wallabies.” Additionally, there were nine other mammals, 13 species of birds, the motorbike frog, and the snake-eyed skink. The woodland analysis also detected DNA from the red fox, house mouse, and black rat — invasive species not native to Australia.
To substantiate that the webs were capturing DNA from local animals, Newton also collected samples at the Perth Zoo, where webs contained DNA from 21 birds, five reptiles, two amphibians, and 33 mammals, including giraffes, elephants, rhinos, orangutans, lemurs, and meerkats. In essence, the technique was effective. It represents a novel means of monitoring animal biodiversity and notifying us when we should act to conserve native species and intensify efforts to eradicate invasive ones. “I think it’s clever and cute,” says Elizabeth Clare, a molecular ecologist at York University in Toronto, who was not involved in the study. “It’s a nice noninvasive way of sampling for terrestrial vertebrates. There are thousands of papers examining the movement of DNA through water and very few on land. Therefore, we truly need more explorations like this to start narrowing down how far the material travels, how it accumulates, and how long these signals persist.” For example, Newton is uncertain whether the webs he collected had been in place for days, weeks, or months. However, certain orb spiders spin a new web every night and dismantle it in the morning. “Imagine if you could obtain DNA from those spiderwebs,” says Allentoft. “Then they would capture at a very precise time point the species currently present in the area.” Next, Newton and Allentoft will examine what the placement and durability of webs from different spider species can reveal about the animals in the vicinity. It’s their version of the world wide web — equally packed with vital information.
