Effects of surface sterilization on diet metabarcoding data of invertebrate consumers

Background: DNA metabarcoding is an emerging tool to quantify interactions in challenging environments and consumer groups, including very small taxa where traditional diet analyses are unviable. However, this often requires DNA extraction from full body parts and it is unclear if surface contamination alters diet measures. Methods: We examine different measures of diet (consumption frequency, abundance, diversity, and composition) in two different environments (mesocosm = offered a known diet item; natural = allowed to feed on naturally-occurring diet items) with a group of invertebrate consumers (the spider Heteropoda venatoria) using DNA metabarcoding of full body parts (opisthosomas). We surface sterilized half of the consumers in 10% commercial bleach solution followed by deionized water, leaving the other half unsterilized to examine how surface sterilization may alter diet measures. Results: We found that surface contaminants do not significantly alter any measure of diet (consumption, abundance, diversity, or composition) for consumers collected in either environment. However, in a mesocosm environment, we found marginally significant evidence that surface contamination from shared space with the offered diet item inflated consumption (a reduction from 91% detection to 50% with sterilization), though the results were marginally significant (p-value = 0.07). Conclusion: Surface sterilization does not seem to be a critical need for DNA metabarcoding of full body parts of invertebrate consumers. However, given equivocal results of the effect of surface sterilization in mesocosms, we suggest that surface sterilization should be a first step in diet DNA metabarcoding studies in these contexts where environmental conditions increase the likelihood of surface contamination.