Terrestrial vertebrates face significant threats from human activities worldwide, leading to rapid biodiversity loss, particularly in the tropics. This loss affects ecosystem functions, such as seed dispersal, and can facilitate pathogen transmission. Monitoring vertebrate distributions is crucial for understanding changes in biodiversity and ecosystems and developing adaptive management strategies. Environmental DNA (eDNA) methods have emerged as promising tools for such efforts. Recent advancements show that terrestrial vertebrates leave DNA in the environment through airborne particles, vegetation contact, or when particles settle. Additionally, DNA can stick to various plant parts. Exploring these new substrates has opened up innovative approaches for terrestrial vertebrate biomonitoring, including swabbing vegetation, using rollers or sticky tape on tree trunks and branches, and collecting eDNA from rainwash and flowers.
Collecting eDNA from Leaf Swabs
In a pioneering study, researchers collected leaf swabs at three locations in Kibale National Park, a biodiversity hotspot in Uganda, East Africa. Each of the 24 eDNA samples was obtained by swabbing leaves continuously for three minutes using a swab dipped in a DNA-preserving buffer. After collecting samples, the researchers placed each swab in its own tube containing the DNA-preserving buffer. This buffer protected the DNA on the swabs during transport to the laboratory, eliminating the need for refrigeration. Once in the lab, scientists extracted the DNA from the swabs and analysed it using a technique called “DNA fingerprinting.” They targeted specific genetic markers found in mammals and other vertebrates, running multiple tests on each sample to ensure accuracy. The researchers then filtered out any DNA belonging to humans or domestic animals, focusing solely on the wildlife species of interest.
Detecting the Hidden Diversity of Terrestrial Vertebrates
Despite a small sample size, the study detected 52 vertebrate genera, including amphibians, fish, birds, and mammals. What is more impressive is that each cotton swab used in the study managed to pick up DNA from an average of 7.6 different genera. The researchers were able to identify 30 of these genera down to the species level, all of which are known to inhabit Kibale National Park. Among the identified mammals were three flying species, five tree-dwelling species, and five ground-dwelling species. The smallest mammal detected was the Stella wood mouse (Hylomyscus stella), while the largest was the African elephant (Loxodonta africana). As for birds, the study found 13 perching species, three ground-dwelling species, and one species that can adapt to various habitats. The tiniest bird identified was the Variable sunbird (Cinnyris venustus), and the largest was the Grey crowned crane (Balearica regulorum). The results from this study proved that vertebrate DNA can accumulate on leaves. The unique surface of leaves makes them perfect natural DNA traps, opening up new possibilities for non-invasive wildlife monitoring.
Implications in Biomonitoring and Conservation Research
The results show that leaf swabs are effective for detecting a broad range of terrestrial vertebrates, including cryptic, nocturnal, and arboreal species. Traditional survey methods, such as camera trapping, often miss these species and require extensive time to collect and analyse data. In contrast, the eDNA swabbing method provides a rapid and broad assessment of terrestrial biodiversity. Swabbing is more straightforward and quicker than airborne eDNA collection, requiring only basic equipment and taking minutes per sample. Moreover, swabs can be easily automated in diagnostic labs, facilitating large-scale biomonitoring. Given its simplicity and high detection rate, this method could revolutionise terrestrial biomonitoring, enhance conservation efforts, and support citizen science initiatives, helping to track ecosystem changes and inform adaptive management.
Pioneering a New Era in Ecological Monitoring
The eDNA swabbing approach is a game-changer for monitoring terrestrial vertebrates. It offers a tool to broadly sample biodiversity, addressing the limitations of visual observation methods and providing a scalable solution for large-scale biomonitoring. Unlike passive air sampling, which has a lower vertebrate detection rate and requires extensive setup, the swabbing method is straightforward, efficient, and easily integrated into existing workflows. The study’s findings underscore the potential of leaf swabs for tracking changes in ecosystem composition and function, influenced by human activities. This approach supports adaptive management strategies and enhances conservation efforts by facilitating rapid, large-scale data collection. The low-tech, simple collection method is ideal for citizen science projects and can be a powerful tool for ecosystem monitoring and management. The breakthrough discovery of using leaf swabs for eDNA collection presents a promising future for terrestrial vertebrate biomonitoring, emphasising the need for continued research and application in diverse environments.
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