234 / 2024-02-28 13:58:44

Detection of terrestrial species using environmental DNA during heavy rainfall events and associated influencing factors

environmental DNA,terrestrial mammals,turbid water,pore size,digital PCR,generalized linear mixed model

Recent developments in environmental DNA (eDNA) techniques have facilitated the monitoring of terrestrial species. The concept of eDNA refers to DNA released by organisms in the environment (e.g., sea, lakes, and soil) through skin fragments, mucus, and excreta that allows to determine the presence or absence of species based on the detectability of the target DNA. However, due to infrequently released DNA into aquatic environments, an efficient sampling design for eDNA of terrestrial species using aquatic eDNA has not yet established. In this study, we applied eDNA technology to turbid water sampled in three rivers and one irrigation channel within the Kiyotake River catchment, southwest Japan, during rainfall events of different magnitudes and investigated the detectability of a terrestrial species popularly farmed in the area. We examined the efficiency of eDNA recovery methods using glass fiber filter papers with different pore sizes (0.7 µm and 2.7 µm). DNA extraction was performed using the DNeasy PowerSoil Kit and the species-specific DNA concentration was quantified using primers and probes targeting the mitochondrial cytochrome b (Cytb) region on a digital PCR (dPCR) system. We also assessed the influence of various environmental factors (e.g., rainfall characteristics described by the parameters of gaussian distribution, water turbidity) on eDNA detection across different rainfall events. During the surveys, the target DNA was detected in 42 out of 47 samples, suggesting the feasibility of stable detection of terrestrial species from stormwater. Overall, compared with the glass fiber filter with larger pores (GF/D), that with the smaller pore size (GF/F) captured more eDNA. However, in high turbidity samples, GF/D captured more eDNA. Generalized linear mixed model revealed that the prolonged rainfall duration, turbidity, and pH had a significant positive effect on eDNA concentration, whereas the distance from the assumed point of entry into the river to the sampling point had a significant negative effect. These results suggest that the runoff and transport of eDNA from terrestrial areas to rivers are enhanced under prolonged rainfall conditions although eDNA degrades while transported along a longer watercourse by biochemical decomposition and sedimentation.