Approximating abundance of Daphnia dentifera using environmental DNA (eDNA) samples

Emily Landolt, a student in St. Norbert College, worked in the lab of Dr. Alex Strauss

Abstract Freshwater zooplankton, such as Daphnia dentifera, are helpful model organisms for studying infectious disease dynamics and are ecologically important because of their role in food webs. They are consumers of primary producers like algae and are prey for other organisms such as fish. However, field sampling of freshwater zooplankton can be costly in terms of time and effort. The use of eDNA to estimate species abundances rather than an assessment of presence/absence in aquatic ecosystems is an exciting concept because it allows for more efficient and potentially more accurate field sampling. eDNA sampling methods for this study system can also be important for monitoring populations and epidemics in the field to ensure ecosystem health. This methodology has been studied in fish but is not yet well understood for invertebrates. We explored this idea by generating artificial mesocosm populations of Daphnia. Sampling for species abundance was done in two ways: using a traditional observational method of taking a subsample and counting the number of Daphnia, and a novel molecular method to quantify the amount of eDNA using a qPCR assay. Our results are a correlation between the observed species abundance and the molecular quantification of eDNA. Preliminary results show insignificant relationships indicating complexity that needs to be explored. Possible factors that affected the amount of eDNA in the water include water chemistry (i.e. pH), age structure, time since introduction, and water replenishment from evaporation/sampling. In the future, more research will be needed to explore the factors of eDNA persistence and how it can be used to better approximate species abundances of aquatic invertebrates like Daphnia.