A source-state-space (S3) framework for quantifying environmental DNA fate: bridging mechanism to predictive monitoring

Environmental DNA (eDNA) has revolutionized the area of biodiversity monitoring, although its use as a quantitative method has not been utilized. The most important obstacle is eDNA fate, the complicated process of organism to the sample, which makes the interpretation of the signal more difficult. In order to meet this difficulty, we propose a single, mathematically explicit Source-State-Space (S 3 ) framework. The S 3 model combines the interrelated mechanisms of eDNA dynamics: release (Source), environmental contacts and maintenance (State), and spatial displacement (Space). It breaks down the identified eDNA signal as: In this equation, f (Source) is the biological determinant of variability in eDNA shedding due to lysis-associated and lysis-free release, g (State) is the modulation of eDNA persistence through particle adsorption and the recently outlined pollutant-induced structural sensitization mechanism, and h (Space) is the transport due to hydrology and particle mediation. Through the combination of these processes, we address major ambiguities in eDNA data and make S 3 a bridge between molecular ecology and environmental toxicology. To transform eDNA into a predictive and not merely a detection tool, the future research must concentrate on parameterizing the S 3 functions, quantifying shedding variability and explaining ecotoxicological influences on eDNA stability. This review offers a mechanistic framework and conceptual map of how eDNA sampling designs could be optimized and signal interpretation enhanced to make eDNA a useful quantitative instrument in the conservation of biodiversity in a fast-evolving world.