CORRESPONDENCE Response to Casey et al.’s sensitivity of detecting environmental DNA comment Christopher L. Jerde 1 , Derryl J. Miller 1 , Andrew R. Mahon 2 , W. Lindsay Chadderton 3 , & David M. Lodge 1 1 Department of Biological Sciences, Environmental Change Initiative, University of Notre Dame, Notre Dame, IN 46556, USA 2 Department of Biology, Institute for Great Lakes Resources, Central Michigan University, Mt. Pleasant, MI 48859, USA 3 The Nature Conservancy, Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA Correspondence Christopher L. Jerde, Environmental Change Initiative, 1400 East Angela Boulevard, South Bend, Indiana 46617, USA. Tel: 574-217-0267; Fax: 574-631-7413. E-mail: cjerde@nd.edu Received 16 February 2012 Accepted 16 February 2012 Editor Phillip Levin doi: 10.1111/j.1755-263X.2012.00231.x Casey et al. correctly identified a need for clarification re- garding the detection limits we reported for two PCR as- says (Jerde et al. 2011). Serial dilutions of purified PCR amplicon DNA (not total genomic DNA) were used to evaluate sensitivity. One microliter of purified ampli- con DNA from each assay was added to 25 μL reac- tions and the lowest detectable concentrations were ap- proximately 207 copies/μL of DNA (3.30 × 10 −8 ng/μL) for bighead carp, and 7 copies/μL of DNA (7.25 × 10 −10 ng/μL) for silver carp. We determined the maxi- mum sensitivity of our assays under ideal laboratory de- tection conditions because the detection limits of any PCR assay for bulk environmental samples is contingent on the complexity of the assayed DNA solution and water quality characteristics (Thompson et al. 2006). This clar- ification about the type of DNA used in the assay, that is amplicon DNA rather than total genomic DNA to de- termine maximum sensitivity, eliminates the concern of Casey et al. regarding credibility of our eDNA assays. No conclusions or observations reported by Jerde et al. (2011) are affected by the concerns raised by Casey et al. including: the sensitivity of eDNA surveil- lance exceeding that of traditional monitoring tools (Figure 3; Jerde et al. 2011); the presence of Asian carp above the electric barrier where eDNA first detected them (Figure S1; Jerde et al. 2011); and the eDNA approach, which has been applied by the U.S. Army Corps of Engineers using the protocols and procedures from our study resulting in similar detection patterns (http://www.lrc.usace.army.mil/AsianCarp/eDNA.htm). Finally, a number of recent studies demonstrate that eDNA is a reliable index of the occurrence and abun- dance of rare aquatic macrofauna (Dejean et al. 2011; Goldberg et al. 2011; Minamoto et al. 2011; Thomsen et al. 2012). References Dejean, T., Valentini A., Duparc A., Pellier-Cuit S. et al. (2011) Persistence of environmental DNA in freshwater ecosystems. PLoS One 6, e23398. Goldberg, C.S., Pilliod D.S., Arkle R.S., Waits L.P. (2011) Molecular detection of vertebrates in stream water: a demonstration using rocky mountain tailed frogs and idaho giant salamanders. PLoS One 6, e22746. Jerde, C.L., Mahon A.R., Chadderton W.L., Lodge D.M. (2011) “Sight-unseen” detection of rare aquatic species using environmental DNA. Conserv Lett 4, 150–157. Conservation Letters 0 (2012) 1–2 Copyright and Photocopying: c  2012 Wiley Periodicals, Inc. 1