A quantitative analysis of vertebrate environmental DNA degradation in soil in response to time, UV light, and temperature

Environmental DNA (eDNA) degradation influences the effectiveness of eDNA-based biodiversity monitoring, but the factors that determine the rate of decay of eDNA in terrestrial environments are poorly understood. We assessed the persistence of vertebrate eDNA from a mock vertebrate community created with soil from zoo enclosures holding 10 target species from different taxonomic classes (reptiles, birds, and mammals) and of different biomass (little penguin and giraffe). We examined species detection rates resulting from eDNA metabarcoding, as well as relative eDNA concentrations via qPCR, from soil samples over eight time points (0–12 weeks), during exposure to three ambient temperatures (10, 25, and 40°C) and three levels of ultraviolet B (UV-B) radiation (0%, 50%, and 100% intensity). We recorded considerable variation in detectability between species, independent of temperature, and UV-B effects. Quantitative polymerase chain reaction (PCR) indicated degradation of eDNA over time for all temperature and UV treatments, although it was still possible to detect eDNA from some species after 12 weeks. Degradation rates were lowest for high UV-B treatments, presumably due to UV-B reducing bacterial metabolism. The temperatures investigated did not influence eDNA decay. Our results indicate that eDNA in soil can persist under a range of temperatures and high UV radiation for longer than expected. Sheltered sites with minimal UV-B radiation, which have previously been considered ideal sites for terrestrial eDNA collection, may not be optimal for eDNA persistence in some cases due to microbial decay. A better understanding of eDNA degradation in terrestrial environments is needed to enhance the accuracy of eDNA metabarcoding for surveying terrestrial vertebrate communities.