Radiotelemetry reveals effects of upstream biomass and UV exposure on environmental DNA occupancy and detection for a large freshwater turtle

Abstract

Background: Imperfect detection of hard-to-sample organisms has motivated the development of novel monitoring techniques. Environmental DNA (eDNA) can provide a sensitive, relatively low-cost sampling method in aquatic systems, but biotic and abiotic factors can affect its reliability. Aims: We used a reintroduced population of radio-tracked alligator snapping turtles (Macrochelys temminckii) to test the efficacy and ecology of eDNA in a lotic system. Materials & Methods: We collected samples at turtle locations as well as random up- and downstream sites. Using a novel eDNA assay, we modeled occupancy and detection of eDNA using turtle biomass and remotely sensed UV exposure and also tested the relationship between these parameters and eDNA concentration. Results: We found eDNA occupancy was best explained by upstream biomass and detection probability decreased with greater upstream UV exposure. The concentration of eDNA in a sample was not significantly affected by biomass measures, but decreased with higher upstream UV exposure, and the effect was significant. Discussion: Our results show that UV exposure can affect aquatic eDNA sampling in situ with free-ranging animals. The use of radiotelemetry allowed for higher control when modeling eDNA persistence and transport in a natural setting relative to laboratory, enclosure, or mesocosm studies. Conclusion: We propose using wildlife tracking techniques to provide added realism to studies of eDNA dynamics.