Margaritifera monodonta, or the Spectaclecase Mussel, is a federally endangered freshwater mussel species that has experienced a 55% reduction in range and is currently concentrated in 3 rivers in the Midwest region of the United States (Gasconade and Meramec rivers, Missouri, and St Croix River, Wisconsin). The detection of new populations by traditional survey methods has been limited because these mussels tend to occur under large rocks and boulders. Environmental DNA (eDNA) technology has been used to detect invasive and rare species, but its use for detection of rare, benthic-dwelling species in large flowing systems has been limited. Here, we propose using eDNA to assess known populations of M. monodonta. We designed a M. monodonta-specific quantitative polymerase chain reaction (qPCR) assay and tested it using water samples from multiple M. monodonta housing tanks, water samples from 2 known mussel beds on the St Croix River, and water samples from 3 known mussel beds on the Mississippi River. We observed higher overall eDNA detection rates on the St Croix River (30.2%) compared to the upper Mississippi River (0.60%). We also observed higher eDNA detection rates (73.3-93.1%) in 2018 for samples collected during the larval release period in May compared to samples collected in August after the reproductive period had ended (55.6-70.8%) on the St Croix River. We tested samples collected at 3 distances downstream from the 2 mussel beds found in the St Croix River, but we did not observe a substantial effect of distance on our detection rates. However, we did observe greater detection rates for samples collected near the bottom compared to at the surface. Our results indicate that this novel qPCR assay can successfully detect M. monodonta eDNA and could be used to rapidly screen locations to guide intensive physical searches for populations in riverine systems.
Aim To evaluate the ability of precipitation‐based environmental DNA (eDNA) sample collection and mitochondrial 12S metabarcoding sequencing to reconstruct well‐studied fish communities in lakes and rivers. Specific objectives were to 1) determine correlations between eDNA species detections and known community composition based on conventional field sampling, 2) compare efficiency of eDNA to detect fish biodiversity among systems with variable morphologies and trophic states, and 3) determine if species habitat preferences predict eDNA detection. Location Upper Great Lakes Region, North America. Methods Fish community composition was estimated for seven lakes and two Mississippi River navigation pools using sequence data from the mitochondrial 12S gene amplified from 10 to 50 water samples per waterbody collected in 50‐mL centrifuge tubes at a single time point. Environmental DNA (eDNA) was concentrated without filtration by centrifuging samples to reduce per‐sample handling time. Taxonomic detections from eDNA were compared to established community monitoring databases containing up to 40 years of sampling and a detailed habitat/substrate preference matrix to identify patterns of bias. Results Mitochondrial 12S gene metabarcoding detected 15%–47% of the known species at each waterbody and 30%–76% of known genera. Non‐metric multidimensional scaling (NMDS) assessment of the community structure indicated that eDNA‐detected communities grouped in a similar pattern as known communities. Discriminant analysis of principal components indicated that there was a high degree of overlap in habitat/substrate preference of eDNA‐detected and eDNA‐undetected species suggesting limited habitat bias for eDNA sampling. Main conclusions Large numbers of small volume samples sequenced at the mitochondrial 12S gene can describe the coarse community structure of freshwater systems. However, additional conventional sampling and environmental DNA sampling may be necessary for a complete diversity census.
Common loon (Gavia immer (Brünnich, 1764)) foraging patterns and the relative importance of cisco (Coregonus artedi Lesueur, 1818) in the diets of loons were evaluated for the Whitefish Chain of Lakes, a set of cold-water cisco refuge lakes in Minnesota, USA. Environmental DNA metabarcoding of loon fecal samples detected 15 fish species. Yellow perch (Perca flavescens (Mitchill, 1814)), mimic shiner (Notropis volucellus (Cope, 1865)), and cisco were the most prominent prey detected across the study lakes. We observed a shift in fish species consumed, with increases in detections of mimic shiner and cisco DNA among loon fecal samples collected in August and September. In some locations, suitable oxythermal habitat became restricted throughout the summer, forcing cisco into surface waters which potentially increased their vulnerability to loon predation. Conversely, large foraging aggregations of loons were observed during late summer through fall at locations with ample oxythermal habitat and abundant cisco populations. We hypothesize that cisco were sought by loons as a high-calorie prey resource prior to migration. Conservation efforts directed at preserving water quality in important cisco refuge lakes are likely to benefit common loons through enhancement of both the forage base, for resident and migrating birds, and breeding habitat suitability.
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