Abstract
Environmental managers require a sensitive and reliable means to prove, with the highest level of confidence possible, where non-native fish species exist and where they do not. Therefore, a nested PCR (nPCR) protocol was developed to detect the environmental DNA (eDNA) of a case-study species, topmouth gudgeon Pseudorasbora parva, which was recently the subject of a national eradication campaign in the UK. The nPCR protocol was tested in the laboratory and in the field in a series of coordinated surveys (eDNA and conventional sampling with traps) at a commercial angling venue in southern England where an initial eDNA survey, based on conventional PCR (cPCR), found P. parva to be present in one of the seven ponds. In the laboratory, the nPCR protocol was on average 100× more sensitive than cPCR, providing a 100% detection rate at DNA concentrations of 3 × 10−8 ng/µL (8 DNA copies per µL). In the field, nPCR and conventional trapping both detected P. parva in only one of the seven angling ponds, the same infested pond as in the previous cPCR-based study. Following eradication work on the infested pond, no eDNA of P. parva was detected using nPCR in either the formerly-infested pond or the adjacent pond, which had been used to quarantine large commercially-valuable fishes. In management applications where the veracity of negative results may be of equal importance as confirmation of positive detections, nPCR protocols provide a useful addition to the analytical toolkit available to inform decision makers responsible for non-native species management.
Highlights
A major challenge in the conservation and management of aquatic ecosystems to combat biological invasions is the detection of non-native species (NNS), both as an early warning after their initial introduction and as a means of determining where to apply management procedures to eradicate or contain the unwanted NNS (Simberloff et al 2005)
In the UK, where it arrived via the same vector in the mid-1980s, P. parva has been the subject of a nationwide eradication campaign due to the potential threats the species poses to native fish species (Gozlan et al 2005; Britton et al 2007; Great Britain Non-native Species Secretariat 2015)
An eradication attempt was conducted by the fishery owners, but the persistence of a low-density population of P. parva was confirmed by conventional PCR (cPCR) of water samples and focused intensive trapping at the locations where DNA of P. parva was found (Davison et al 2017)
Summary
A major challenge in the conservation and management of aquatic ecosystems to combat biological invasions is the detection of non-native species (NNS), both as an early warning after their initial introduction and as a means of determining where to apply management procedures to eradicate or contain the unwanted NNS (Simberloff et al 2005) To address this challenge, molecular techniques are being developed to detect species, even when present in very low abundance, from the environmental DNA (eDNA) that these organisms shed into the aquatic environment (Darling and Mahon 2011; Rees et al 2014; Davison et al 2016). At a recreational angling venue in southeast England, conventional PCR-based eDNA analysis provided evidence, of sufficiently high degree of confidence to form the basis of management decisions, that P. parva had survived an attempted eradication in one pond but was not present in six adjacent but unconnected ponds (Davison et al 2017)
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