Over the past few years our perception of the term “environmental DNA” (eDNA) has subtly moved away from the historical use of the term, that could refer to DNA derived from any environmental source, to refer specifically to “free” eDNA and/or DNA derived from organisms without prior removal from their substrate. Free forms of eDNA are most likely derived from cellular material derived from organisms as they pass through an environment, or die and decay. Irrespective of specific terminology, using eDNA to detect the presence of a broad range of organisms has had substantial impact, not least with stakeholder organisations acknowledging eDNA analysis as evidence of the presence of rare, or endangered species in freshwater ecosystems. Simultaneously a large number of groups around the world are converging on using eDNA approaches to detect alien invasive species and/or to develop early warning sensor systems. To date, by far the largest proportion of eDNA studies have employed forms of quantitative PCR (qPCR) to assess the biodiversity of single species, but clearly, the potential for using simultaneous species assessment methodologies such as metabarcoding and shotgun sequencing offer opportunities for community assessment at the habitat, if not ecosystem scale. Nevertheless, a large number of questions still remain unanswered regarding the ecological relevance of eDNA in the wild. For example, we need to identify precisely what different forms of eDNA are, what factors affect the persistence of detectable fragments of eDNA and how eDNA traces relate to living communities in space and time in both lentic and lotic ecosystems.
Results/Conclusions
Here, we will overview insights derived from contemporary research investigating the ecological relevance of freshwater eDNA, from the laboratory to the ecosystem scale and explore findings derived from targeted and broad scale eDNA analysis in relation to the ecological relevance of eDNA. Finally, we will explore emerging projects seeking to fill gaps in our current knowledge and consider the future of eDNA analyses in relation to monitoring ecosystem health and understanding biodiversity-ecosystem functioning relationships.