In an astonishing revelation, just a handful of leaf swabs have unveiled a profound genetic portrait of Uganda's Kibale National Park's diverse wildlife. The findings, reported in Current Biology on August 21, stem from the collection of 24 leaf swabs from park plants, uncovering environmental DNA (eDNA) traces from 52 distinct animals. Remarkably, researchers managed to identify 30 of these animals down to the species level, underscoring the revolutionary potential of this rapid and uncomplicated technique for biodiversity monitoring.
Julie Lockwood, a biologist at Rutgers University in New Brunswick, New Jersey, who was not part of the study, lauded the researchers, describing their ability to glean such a wealth of species data from a few leaves as "cool and remarkable."
Contrary to the conventional notion of DNA confined within cells, genetic material particles are dispersed throughout the environment as eDNA. This genetic residue often accumulates in various locations, such as bodies of water or on surfaces like tree bark, offering insights into the resident species, including those that prove elusive to conventional observation.
Biologist Jan Gogarten from the University of Greifswald in Germany sought to compare his eDNA source—flies that collect DNA from deceased animals and feces—with biologist Christina Lynggaard's technique of collecting eDNA from the air. While both researchers intended to assess their methods in Kibale, the process of setting up air filters proved time-consuming. Consequently, Gogarten seized the opportunity to swab nearby leaves during the wait—a spontaneous decision that yielded exceptional results.
The swabbing process, conducted across three park areas, lasted a mere 72 minutes, averaging three minutes per swab. In contrast, Lynggaard previously ran air filters for at least 30 minutes each in a prior study, not including setup and cleanup time. Subsequently, the researchers transported the swabs back to Denmark for analysis.
The eDNA analysis uncovered numerous iconic avian and mammalian species known to inhabit the park, such as the great blue turaco (Corythaeola cristata) and the African bush elephant (Loxodonta africana). Surprisingly, there were unexpected findings as well. Colin Chapman, another project collaborator and a biologist at Vancouver Island University in Nanaimo, Canada, who has studied the forest for over three decades, noted bird species on the list that he had never personally encountered, although others had sighted them in the park. This underscores the hidden biodiversity eDNA can unveil.
Furthermore, these swabs offer superior fieldwork convenience compared to other sampling devices. For instance, Lockwood collects eDNA from plant surfaces using paint rollers. With the compact swabs, preserving and transporting them back to the lab becomes a straightforward task, enhancing their utility.
Given the global decline in biodiversity, techniques like leaf swabs for eDNA sampling represent a revolutionary step toward documenting and responding to these changes. Lockwood underscores the significance of having a diverse toolkit for eDNA collection and processing, emphasizing that "There's not one tool for gathering the eDNA and processing everything that works in every case. So the more tools we have, the better off we are."
Gogarten and Lynggaard hope their swabbing technique will be embraced by various parties, including citizen scientists, in the fight against worldwide biodiversity loss. Lynggaard highlights the user-friendliness of the method, suggesting that "people interested in citizen science could … help researchers fight this biodiversity loss that we're having worldwide." For instance, schoolchildren armed with swabs could sample leaves in their backyards, contributing to a localized biodiversity picture.