a b s t r a c tGenetic identification of aqueous environmental DNA (eDNA) provides site occupancy inferences for rare aquatic macrofauna that are often easier to obtain than direct observations of organisms. This relative ease makes eDNA sampling a valuable tool for conservation biology. Research on the origin, state, transport, and fate of eDNA shed by aquatic macrofauna is needed to describe the spatiotemporal context for eDNA-based occupancy inferences and to guide eDNA sampling design. We tested the hypothesis that eDNA is more concentrated in surficial sediments than in surface water by measuring the concentration of aqueous and sedimentary eDNA from an invasive fish, bigheaded Asian carp (Hypophthalmichthys spp.), in experimental ponds and natural rivers. We modified a simple, low-cost DNA extraction method to yield inhibitor-free eDNA from both sediment and water samples. Carp eDNA was 8-1800 times more concentrated per gram of sediment than per milliliter of water and was detected in sediments up to 132 days after carp removal -five times longer than any previous reports of macrobial eDNA persistence in water. These results may be explained by particle settling and/or retarded degradation of sedimentadsorbed DNA molecules. Compared to aqueous eDNA, sedimentary eDNA could provide a more abundant and longer-lasting source of genetic material for inferring current-or-past site occupancy by aquatic macrofauna, particularly benthic species. However, resuspension and transport of sedimentary eDNA could complicate the spatiotemporal inferences from surface water sampling, which is currently the predominant eDNA-based approach. We discuss these implications in the context of conservation-oriented monitoring in aquatic ecosystems.
Detection of invasive species before or soon after they establish in novel environments is critical to prevent widespread ecological and economic impacts. Environmental DNA (eDNA) surveillance and monitoring is an approach to improve early detection efforts. Here we describe a large-scale conservation application of a quantitative polymerase chain reaction assay with a case study for surveillance of a federally listed nuisance species (Ruffe, Gymnocephalus cernua) in the Laurentian Great Lakes. Using current Ruffe distribution data and predictions of future Ruffe spread derived from a recently developed model of ballast-mediated dispersal in US waters of the Great Lakes, we designed an eDNA surveillance study to target Ruffe at the putative leading edge of the invasion. We report a much more advanced invasion front for Ruffe than has been indicated by conventional surveillance methods and we quantify rates of false negative detections (i.e. failure to detect DNA when it is present in a sample). Our results highlight the important role of eDNA surveillance as a sensitive tool to improve early detection efforts for aquatic invasive species and draw attention to the need for an improved understanding of detection errors. Based on axes that reflect the weight of eDNA evidence of species presence and the likelihood of secondary
Two Hawaiian picture-wing Drosophila differ in their temperature tolerances with the ecologically rare species, D. silvestris, showing reduced survival, reduced sperm mobility and greater gene expression changes at high temperatures compared to the common D. sproati. Thus the rare species may have reduced capacity to adapt to future climate changes.
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