Environmental DNA detection range for hydrilla, a prolific invasive plant

Environmental DNA (eDNA) is a powerful conservation tool that has made significant advancements in the past decade. Since its initial application in 2008 to detect invasive tadpoles, eDNA has become popular for finding rare and invasive species that are otherwise difficult to detect through traditional field sampling methods. This study sought to determine a detectable range of eDNA for an aggressively invasive aquatic plant species, Hydrilla verticillata (L. f.) Royle, as well as to understand how stream discharge affects eDNA detection distance. To do so, we surveyed downstream of a large reservoir, which is separated from its distributary by a dam. Hydrilla verticillata is present in the reservoir but absent in the distributary. We used correlation analysis to understand the relationship between transportation distance and detection. We also built upon a model developed by Pont et al. (2018) to assess the relationships between stream discharge and eDNA detection distance, as well as to compare this relationship for our plant-based eDNA study with previous animal-based studies. By utilizing this natural system and surveying at different points downstream of the known population, this study detected H. verticillata eDNA nearly 5 km from the source population. This study, which is the 1st known instance of correlating plant eDNA to animal eDNA detection ranges, suggests the genetic material of both kingdoms are similarly detectable in flowing freshwaters and supports other studies that suggest discharge is a strong predictor of the detectable distance of eDNA.