Risk analysis of species invasions links biology and economics, is increasingly mandated by international and national policies, and enables improved management of invasive species. Biological invasions proceed through a series of transition probabilities (i.e., introduction, establishment, spread, and impact), and each of these presents opportunities for management. Recent research advances have improved estimates of probability and associated uncertainty. Improvements have come from species-specific trait-based risk assessments (of estimates of introduction, establishment, spread, and impact probabilities, especially from pathways of commerce in living organisms), spatially explicit dispersal models (introduction and spread, especially from transportation pathways), and species distribution models (establishment, spread, and impact). Results of these forecasting models combined with improved and cheaper surveillance technologies and practices [e.g., environmental DNA (eDNA), drones, citizen science] enable more efficient management by focusing surveillance, prevention, eradication, and control efforts on the highest-risk species and locations. Bioeconomic models account for the interacting dynamics within and between ecological and economic systems, and allow decision makers to better understand the financial consequences of alternative management strategies. In general, recent research advances demonstrate that prevention is the policy with the greatest long-term net benefit. 454 Lodge et al.
Environmental DNA (eDNA) is useful for delimiting species ranges in aquatic systems, whereby water samples are screened for the presence of DNA from a single species. However, DNA from many species is collected in every sample, and high-throughput sequencing approaches allow for more passive surveillance where a community of species is identified. In this study, we use active (targeted) and passive molecular surveillance approaches to detect species in the Muskingum River Watershed in Ohio, USA. The presence of bighead carp (Hypophthalmichthys nobilis) eDNA in the Muskingum River Watershed was confirmed with active surveillance using digital droplet polymerase chain reaction (ddPCR). The passive surveillance method detected the presence of eDNA from northern snakehead (Channa argus), which was further confirmed with active ddPCR. Whereas active surveillance may be more sensitive to detecting rare DNA, passive surveillance has the capability of detecting unexpected invasive species. Deploying both active and passive surveillance approaches with the same eDNA samples is beneficial for invasive species management.
The use of environmental DNA is a rapidly evolving approach for surveillance and detection of species. Often water samples are collected in the field and then immediately cooled, filtered, and the resulting filters are stored in freezers to preserve the DNA for subsequent analyses. Recently it was shown that filtered samples could be stored at room temperature for 14 days without any discernable loss in the total DNA. However, for many conservation applications, particularly in remote settings with limited capacity to freeze samples, it would be advantageous to store samples at room temperature for longer periods of time. Here we test for significant loss of DNA yield from storage of polycarbonate track etched filters in Longmire's lysis buffer at room temperature (20°C) for 150 days. Renshaw et al. (2014) demonstrated that eDNA water samples could be collected, filtered using PCTE filters, and then stored in Longmire's lysis buffer at room temperature for 14 days with no difference in DNA yield. The 14-day holding time of their initial evaluation is useful for short duration field collections and for instances where shipments of filtered samples are required. However, with the use of eDNA for surveillance over larger geographic expanses and with samples potentially being collected in very remote areas, it may be necessary to store samples without freezing or refrigeration for longer periods of time.Here we test the effects on eDNA at room temperature using Longmire's lysis buffer for sample preservation for a 150 days.Sterilized 2L Nalgene bottles (bleach wash, rinse, and autoclaving) were filled with river water. One Round Goby (Neogobius melanostomus) was placed in each bottle for approximately 5 min and removed (n = 28). For each sample, we filtered water until the filter paper was clogged or until the full 2 L from the sample passed through. Filter papers were preserved in Longmire's solution (Renshaw et al. 2014). We extracted 16 samples immediately after filtration, and 12 samples were held 150 days at room temperature (ambient) prior to extraction. Following DNA extraction, total eDNA concentrations were measured using a Nanodrop spectrophotometer (Thermo Scientific) and target species eDNA was quantified using digital droplet PCR (ddPCR) and species specific markers for Round Goby (Nathan et al. 2014).From the resulting data for both total eDNA and target species DNA concentrations, we evaluated the difference in eDNA yield between initial conditions at day 0 to samples stored at room temperature for 150 days (Table 1). T test, tests of normality, and correlation tests were conducted in Mathematica 9.0.1.0 (Wolfram Research, Inc.,
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