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Frequently Asked Questions

Below is a list of frequently asked questions. If you have any other questions, please send them in.

  • Does the eDNA technique also detect species that occurred in a water body in the past?
    • No. Experiments have shown that eDNA persists in water for up to 3 weeks. For longer ago than that, no eDNA is detected. Detection of the DNA of a target species therefore indicates the recent presence of that species (click here for publication).
  • Can the eDNA approach be used for detecting species in large water bodies, such as rivers or canals?
    • Yes. In North America , the eDNA technique has shown the presence of exotic carp species in a large canal between the Mississippi Basin and the Great Lakes (Jerde et al., 2011). However, for large water bodies and rivers, the sampling strategy needs to be adjusted. 
  • Can the eDNA approach be used to detect a species in fast-flowing water?
    • Yes. The eDNA technique also works in fast-flowing water. SPYGEN carried out a test where a sturgeon was placed in a cage in a stream. The species was detectable up to a distance of about 500 metres; further away its detectability rapidly declined due to dilution of the eDNA. (unpublished data) In North America, the eDNA technique was successfully applied to detect rare frog and salamander species in fast-flowing streams. In moving water, the exact location of the species can possibly be deduced from the amount of eDNA in the samples; the closer to the species, the more eDNA.
  • How powerful is the environmental DNA method?
    • During a pilot study carried out by RAVON and SPYGEN on the Pond Loach (Misgurnus fossilis) an eDNA sample was taken in the Rijnstrangen, a vast wetland near Zevenaar. Earlier, only one juvenile had been captured from this location despite considerable sampling effort using both electro-fishing and dipnets. The eDNA sample confirmed the presence of the species, the amount of DNA in the sample even suggesting that there must be a significant population (click here for publication (in Dutch!)).
    • In a study carried out by SPYGEN in France, traditional inventory methods were compared to the environmental DNA technique for the detection of the American Bullfrog (Lithobates catesbeianus). With traditional methods, the bullfrog was only found in 7 out of 49 sampled waters, while eDNA technique established the presence of the bullfrog in 38 of the 49 waters.
    • However, the environmental DNA approach is, just like traditional methods, not flawless: during an a large-scale inventory of Misgurnus fossilis carried out by RAVON in 2012, the technique failed to detect the species at a few locations where traditional sampling had revealed its presence. The eDNA approach needs to be further perfected. It is clear that ecological knowledge is needed on when and where to sample. Moreover, to be able to interpret the results, experience with the analysis and awareness of the limitations of the primers are crucial. 
  • Is it possible to determine the density of a species with the eDNA technique?
    • Yes, although we are not yet able to assess the absolute density. Research has shown that the amount of eDNA in a water sample is significantly related to the density of the target species in the water body. However, we first need to know whether the amount of DNA that a species leaves behind in the water varies during the year. In addition, more research is needed into the persistence and breakdown of DNA in various environments, that is environments differing in their microbial communities and abiotic conditions.
If you have other questions, please feel free to contact RAVON.
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