Beyond insects: leveraging bulk arthropod samples for vertebrate biodiversity monitoring using invertebrate-derived DNA (iDNA) metabarcoding
This study demonstrates that invertebrate-derived DNA (iDNA) metabarcoding of bulk arthropod samples collected via malaise traps can effectively complement camera trap surveys for monitoring forest vertebrate biodiversity, successfully detecting a range of native, pest, and domesticated species with high congruence for common and cryptic fauna.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Tracking the hidden lives of animals in a forest has long been a challenge for conservationists. Traditional methods often involve setting traps that can harm creatures or placing cameras that require expensive equipment and months of waiting to capture a single image of a shy animal. In recent years, scientists have turned to a different kind of evidence: genetic material left behind by living things. This approach, known as environmental DNA, involves collecting samples from soil, water, or air to find traces of life. A more specific variation of this technique looks inside the stomachs of insects. Many insects, such as mosquitoes or flies, feed on the blood or flesh of vertebrates like birds, mammals, and reptiles. When these insects are collected, their gut contents hold a tiny, preserved record of the animals they recently bit or ate. By reading this genetic code, researchers can identify which vertebrates are present in an area without ever seeing them directly.
A new study from southwestern Australia explores a clever way to use this method on a larger scale. Instead of hunting for specific blood-sucking insects to test one by one, the researchers took advantage of existing collections of mixed insects gathered by standard monitoring traps. These traps, known as malaise traps, are large tents designed to catch flying insects for general biodiversity surveys. The team asked a simple question: could they find the DNA of vertebrates inside these bulk bags of mixed bugs, effectively turning a routine insect survey into a census of the local mammals, birds, and reptiles? They compared their genetic findings against data from camera traps set up at the same locations to see how well this new approach matched the traditional visual records.
The researchers worked with 54 forest sites across different types of eucalyptus woodlands. At each site, they deployed malaise traps for about two weeks to catch flying insects, which were preserved in alcohol. Simultaneously, they set up motion-sensor cameras for six weeks to photograph the animals moving through the forest. In the laboratory, the team processed the bulk insect samples by grinding them up and extracting the DNA. They used two different genetic markers to search for specific sequences: one that could identify a wide range of vertebrates and another designed specifically for mammals. They then compared the list of animals found in the insect guts against the list of animals captured on camera.
The results showed that the method worked, though with some limitations. From the 54 bags of mixed insects, the genetic analysis identified 17 distinct vertebrate species. These included native mammals like the western grey kangaroo and the western brush wallaby, as well as reptiles and a single bird species. The most common animal found was the western grey kangaroo, which appeared in the insect samples at three-quarters of the sites where it was detected. The study also found evidence of forest pests, such as pigs and rabbits, and farm animals like sheep and horses, likely from nearby agricultural land. When the researchers compared these genetic detections to the camera trap footage, they found a strong agreement for common species. About 78 percent of the forest animals found via insect DNA were also seen by the cameras.
However, the two methods did not tell the exact same story. The camera traps detected a much wider variety of life, finding 62 species in total, including many birds and small, elusive mammals that the insect DNA missed. The genetic method struggled to find birds and reptiles, likely because the specific genetic tools used were better suited for mammals and because the insects collected did not feed on all types of animals equally. Despite this, the insect DNA approach offered unique advantages. It successfully identified three species of small skinks that the cameras failed to catch, likely because these lizards are too small or fast to trigger the camera sensors effectively. The study suggests that while this technique cannot yet replace traditional surveys, it offers a valuable way to extract extra information from samples that are already being collected.
The authors note that this approach is still in its early stages. The genetic signals found in the mixed insect samples are often faint and can be overwhelmed by the DNA of the insects themselves. Furthermore, the study highlights that the insects collected in the traps may have fed on animals from a wider area than just the immediate forest site, meaning the genetic data represents a broader landscape rather than a pinpoint location. Nevertheless, the research demonstrates that existing collections of insects, gathered for other purposes, hold a hidden archive of vertebrate life. By refining the methods to extract more DNA and improve the genetic tools, scientists may soon be able to unlock a richer history of forest biodiversity from the very same jars of insects that have been sitting on shelves for years.
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