eDNA Is Not Always Easy: Methodological Studies for the Advancement of Edna Applications to Fish and Wildlife

Environmental DNA (eDNA) can be an effective tool for detecting low abundance invasive or imperiled species. However, many unknowns related to the physical, chemical and biological aspects of the target organisms and their environment hinder the successful application of eDNA to detect new invasive or imperiled species. Additionally, many eDNA methodological studies have been conducted in laboratory settings and may simplify our understanding of which variables are important to eDNA persistence and detection. Here we summarize our findings from recent methodological studies and present important factors to consider when planning eDNA studies. First, we examined how time to filtration (0-48 h after collection) and storage of water samples before filtration (open vs. chilled in the dark) influence eDNA copy number. We found that water samples kept in the dark and chilled had no significant loss of eDNA copy number relative to those filtered directly from the field, whereas water samples kept at room temperature and exposed to light had non-detections at ~12 h. Next, we examined whether crayfish carcasses would produce detectable eDNA in a stream over 28 days. We found that carcasses never produced detectable eDNA, suggesting that for similar species and habitats, detections may indicate only live organisms. Then we assessed how stream flow, seasonality, and density of an invasive clam would impact eDNA copy number. Our results suggest that stream flow can dilute eDNA and result in non-detections, even when the target organism is abundant. In addition, we report a strong influence of seasonality on eDNA copy number and confirm previous findings that sampling during periods of biological activity results in greater probability of detection. Additionally, we found a positive relationship between the density of clams and eDNA copy number. Lastly, we will present preliminary results on whether eDNA can be used to successfully detect terrestrial salamanders.