Insect Soup on Menu at Speedy DNA Cafe

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Quick quiz: What is the physical difference between two nearly identical butterflies, the monarch (Danaus plexippus) and the viceroy (Limenitis archippus)?

If you didn’t know that the viceroy has a black line on its rear wing, you just experienced the same problem facing biologists as they conduct insect population studies used in conservation efforts. Identifying species often requires a taxonomist’s specialized knowledge. Normally, to complete a detailed population survey, taxonomists painstakingly inspect and classify thousands of individual insects.

DNA testing of an “insect soup” made from bugs trapped in a particular area may take the tedium out of taxonomy. The technique, known as metabarcoding, relies on a massive catalog of known genetic markers for particular species, the Barcode of Life Database. Metabarcoding compares these genetic signatures to the DNA found in a soup made from insects and other species collected from the wild. Scientists then estimate the types and quantities of wildlife in an ecosystem using the results from the DNA marker matching game.

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“We collected lots of insects and other creepy-crawlies, ground them up into an ‘insect soup,’ and read the DNA using sequencers that are now cheap enough to use weekly or even daily,” said Douglas Yu of the University of East Anglia in a press release.

Yu and his team collected insects and spiders from three different environments: subtropical forest in China, temperate woodland in the United Kingdoms and tropical rainforest in Malaysia. The metabarcoding of these three servings of bug soup provided a rapid estimate of how many spiders, ants, moths, dung beetles and other insects lived in each region.

The geneticists then cross-checked the three soups’ metabarcoding results against high-quality population datasets collected in Malaysia, China and the UK. These biodiversity datasets required 2,505 hours of taxonomists’ work to compile a list of 55,000 arthropod and bird specimens. Crushing labor requirements makes these highly detailed datasets too expensive for frequent repetition, which limits what scientists know about fluctuations in species numbers.

“We found that our ‘soup’ samples give us the same biodiversity information as the gold-standard datasets,” said Yu. “They are also more comprehensive, many times quicker to produce, less reliant on taxonomic expertise, and they have the added advantage of being verifiable by third parties.”

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Making population studies cheaper and easier can aid scientists and wildlife managers as they make decisions about conservation priorities and strategies.

“For instance, we showed that if the UK Forestry Commission ploughs up some of the grass-covered trackways that run between our endangered heathland habitats, populations of rare spiders, beetles, and other creepy-crawlies can reconnect along those trackways, helping to stave off extinction,” said Yu.

Ecology Letters published Yu’s study: “Reliable, verifiable and efficient monitoring of biodiversity via metabarcoding.”

IMAGES: A viceroy butterfly (Limenitis archippus) in the Lake Erie region. (Kitchin and Hurst/Corbis)

Newly emerged monarch butterfly (Danaus plexippus) and its chrysalis. (Kerri Wile/Getty Images)

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