Environmental conditions influence eDNA particle size distribution in aquatic systems

Abstract

AbstractKnowledge about the size of environmental DNA (eDNA) and eDNA‐bearing particles in aquatic environments is integral to efficient and sensitive analyses. To explore the influence of environmental factors on eDNA particle size distribution (PSD), we manipulated fish communities across nine experimental ponds, which led to differences in a suite of environmental covariates (biochemical oxygen demand, chlorophyll a concentration, conductivity, dissolved oxygen, pH, temperature, and turbidity) over 5 months. At the end of the experiment, we serially filtered water samples from each pond through 5 filter sizes (20, 10, 5, 1, and 0.2 µm) followed by eDNA precipitation. We used quantitative PCR to determine the proportion of Common Carp (Cyprinus carpio) or bigheaded carp (Hypophthalmichthys molitrix and H. nobilis) eDNA captured within each size fraction. Based on eDNA concentrations recorded at each size fraction, we parameterized a Weibull distribution to describe the eDNA PSD of each species in each pond. Likelihood ratio tests suggested that PSD did not differ between species but did differ across ponds. Stepwise multiple regressions indicated that the specific environmental factors with the greatest influence on PSD differed depending on the pore size of the filter used for capture. Notably, positive associations with chlorophyll and turbidity were most important for predicting capture with a 10‐µm filter, suggesting that eDNA is sticky, and the presence of relatively large particles such as algal cells or other suspended sediments can dramatically alter eDNA PSD. Therefore, we advocate that researchers and managers consider analysis of eDNA PSD within their study systems to optimize eDNA capture efficiencies and increase detection probabilities across variable biotic and abiotic conditions. Furthermore, reporting eDNA PSD evaluations across more diverse systems has the potential to reveal broader patterns of eDNA capture efficiency and improve research and natural resource management with eDNA applications.