eDNA State and Medium Affect DNA Degradation Patterns in Seminatural Systems of Southern African Waterholes

Abstract

Environmental DNA (eDNA) has evolved into a valuable asset of the ecologists' toolkit, enabling time- and cost-efficient biodiversity assessments in a wide variety of ecosystems. Since eDNA can be isolated from a broad range of environmental substrates, its persistence times in those media are of decisive importance for drawing inferences about species presence. For the first time, we characterize eDNA persistence in water and sediment samples of seminatural waterholes in a savanna system in South Africa to gain a better understanding of eDNA decay in these waterbodies. Using mesocosm experiments, we tracked eDNA decay in two different DNA states (extracellular and membrane bound), during two different seasons (wet and dry), and from two different substrates (surface water and sediment). Extracellular DNA degraded rapidly in a first-order exponential decay fashion and membrane-bound DNA exhibited a slower decline with more intricate patterns, involving initial reduction followed by a subsequent increase in measured DNA concentrations. The latter we attribute to cell disassociation and cell lysis at 24–48 h after introduction into the environment. Higher stochasticity of membrane-bound DNA capture in the dry season highlights the need for higher sampling efforts in natural systems in which eDNA is presumably more patchily distributed. Additionally, we observed longer eDNA persistence in sediments than in water samples, presumably due to better protection from nucleases. We could not reveal any effects of environmental parameters on eDNA decay, emphasizing that further research is needed to better understand eDNA dynamics in those waterbodies in order to exploit their full potential for eDNA-based bioassessments in those systems.