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RE: Environmental DNA is one tool among many in the biosecurity toolbox

Hewitt, C.L., Campbell, M.L., Dafforn, K., Davis, J., Deveney, M.R., McDonald, J.I., Miller, A. and Sherman, C.D.H. (2018) RE: Environmental DNA is one tool among many in the biosecurity toolbox. Science (eLetters), Jul. 12, 2018 .


In the Perspective "A tool for finding rare marine species: Environmental DNA analysis shows promise for studying rare and elusive marine species" Pikitch (15 June, p. 1180) extolled the virtues of environmental DNA (eDNA), providing a compelling argument for its increasing application (1).
We agree that eDNA can be transformative with significant benefits, particularly high sensitivity for detecting rare species (2) however the challenge for this novel methodology is highly contextual. Marine biosecurity applications of eDNA methods for early detection of new pest incursion are increasing (2-3). However, pin-pointing exact locations and characterising spatial extent can be difficult in a marine context (4), and the detection of DNA from a "pest" does not indicate introduction or establishment. eDNA can persist in the environment for days and even weeks (5,6), suggesting the presence of pest species' DNA could be linked to an extant population, a transient or decomposing individual, or presence in the biofouling or ballast water discharge of a trading vessel (7) at some time in the recent past. To ascertain which of these various possibilities is accurate requires confirmatory sampling. eRNA may aid differentiation of live from dead material and overcome some eDNA constraints, but requires further investigation of the linkages to establishment (5). Additionally, the use of eDNA alone as legal evidence of infection or species' absence is not accepted under global biosecurity frameworks and confirmatory diagnosis is still required (8-10).

Unfortunately, the simplistic presumption that eDNA provides more robust outcomes and can always be used as a substitute for physical sampling and taxonomic analyses is flawed for many systems, and could result in a perverse loss of capability and capacity where needed most. All molecular methods require sound foundations based on alpha-taxonomy. To paraphrase Pikitch, "eDNA should only complement, rather than replace, other research approaches."

Item Type: Non-refereed Article
Publisher: American Association for the Advancement of Science
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