Abstract
Environmental DNA (eDNA) analysis is frequently used as a non-invasive method to investigate species and biodiversity in ecosystems. However, such eDNA may represent both organisms currently present as well as species that released their DNA some point in the past, thereby representing a mix of current and historic biodiversity. This may lead to a false-positive detection of organisms' presence. As the eDNA particle size distribution (PSD) changes along with the decay process, it may facilitate solving the above problem. Here, we set up tank experiments with snails, zebrafish and daphnids, respectively, to monitor the change in eDNA PSD and eDNA degradation through time after removing organisms. We found that zebrafish eDNA decays more slowly for larger particle sizes. Across all species tested, the percentage of large size ranges tended to increase over time while the smaller sizes showed relatively fast decay rates. As a result, PSD changed consistently with eDNA decay, although initial PSD varied between species. In combination, we propose that eDNA PSD can be used to assess the current prevalence of organisms at an eDNA sampling location while avoiding false-positives on the presence of species. Our findings expand the applicability of eDNA for monitoring target species in freshwater ecosystems.
Highlights
Over the last decade, environmental DNA analysis has been successfully used to investigate the presence of aquatic macroorganisms (Alzaylaee et al, 2020; Brys et al, 2021; Holman et al, 2019; Mauvisseau et al, 2019)
We determined the environmental DNA (eDNA) concentration at five particle size ranges of three species separately at six time points after removing the organisms (Fig. 2), thereby assessing how the eDNA particle size distribution (PSD) changed with degree of eDNA degradation
For daphnia eDNA, the PSD may vary with conditions as it was found to be most prevalent in the 0.2-1 μm size range at 20 °C (Moushomi et al, 2019), while we found daphnia eDNA particles to be most abundant in the 1.2-5 μm size range at 22 °C
Summary
Environmental DNA (eDNA) analysis has been successfully used to investigate the presence of aquatic macroorganisms (Alzaylaee et al, 2020; Brys et al, 2021; Holman et al, 2019; Mauvisseau et al, 2019). After shedding, eDNA can persist for several days in a variety of water types (Barnes et al, 2014; Collins et al, 2018; Eichmiller et al, 2016; Strickler et al, 2015) and can move over hundreds of meters in aquatic systems, possibly leading to detection of eDNA while that organism is not or has never been physically present at that DNA sampling site (Bedwell and Goldberg, 2020; Deutschmann et al, 2019; Fremier et al, 2019) Both temporal and spatial factors can cause a mislinkage between the eDNA measured and the actual presence of the organism at a sampling site. This may lead to false-positive detection of species using eDNA techniques, i.e. when eDNA is detected but the species is absent (Buxton et al, 2021; Ficetola et al, 2015), which in turn can result in incorrect inferences on aquatic biomonitoring and corresponding water management measures
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