Persistence of DNA in Carcasses, Slime and Avian Feces May Affect Interpretation of Environmental DNA Data

<div><p>The prevention of non-indigenous aquatic invasive species spreading into new areas is a goal of many resource managers. New techniques have been developed to survey for species that are difficult to capture with conventional gears that involve the detection of their DNA in water samples (eDNA). This technique is currently used to track the invasion of bigheaded carps (silver carp and bighead carp; <i>Hypophthalmichthys molitrix</i> and <i>H. nobilis</i>) in the Chicago Area Waterway System and Upper Mississippi River. In both systems DNA has been detected from silver carp without the capture of a live fish, which has led to some uncertainty about the source of the DNA. The potential contribution to eDNA by vectors and fomites has not been explored. Because barges move from areas with a high abundance of bigheaded carps to areas monitored for the potential presence of silver carp, we used juvenile silver carp to simulate the barge transport of dead bigheaded carp carcasses, slime residue, and predator feces to determine the potential of these sources to supply DNA to uninhabited waters where it could be detected and misinterpreted as indicative of the presence of live bigheaded carp. Our results indicate that all three vectors are feasible sources of detectable eDNA for at least one month after their deposition. This suggests that current monitoring programs must consider alternative vectors of DNA in the environment and consider alternative strategies to minimize the detection of DNA not directly released from live bigheaded carps.</p></div

Detection of silver carp DNA from slime adhering to metal trays.

<p>A plus (+) indicates a positive detection of silver carp DNA over time among triplicate swabs from silver carp slime accumulated on metal trays. A minus (−) indicates no detection of silver carp DNA. NA indicates discarded data due to contamination detected in extraction negative controls.</p><p>Detection of silver carp DNA from slime adhering to metal trays.</p

Detection of silver carp DNA from water in contact with a silver carp carcass.

<p>A plus (+) indicates a positive detection of silver carp DNA over time among triplicate water samples from chambers containing a juvenile silver carp carcass. A minus (−) indicates no detection of silver carp DNA.</p><p>Detection of silver carp DNA from water in contact with a silver carp carcass.</p