A tale of two fluids: does storing specimens together in liquid preservative cause DNA cross-contamination in molecular gut-content studies?

The study of food webs and trophic interactions increasingly relies on PCR-based molecular gut-content analysis. However, this technique may be prone to error from contamination of minute quantities of DNA; i.e., simply storing specimens together in a liquid medium may lead to cross-contamination. In this study, we used PCR to determine the contamination rate when (1) specimens were stored together in 95% ethanol for various time periods, and (2) predators fall into ethylene glycol-filled pitfall traps where the dying predator may inadvertently consume prey DNA-contaminated liquid. We designed experiments and PCR primers to quantify the risk of contamination for both situations and found no contamination by storing specimens together in 95% ethanol. Furthermore, zero predators contained prey DNA in their gut contents from imbibing prey DNA-contaminated ethylene glycol. These results support the use of mass sampling techniques, like wet pitfall traps, for molecular gut-content analysis.