Limited detection of secondarily consumed plant food by DNA‐based diet analysis of omnivorous carabid beetles

Abstract

Abstract Trophic interactions are monitored by molecular methods based on the identification of prey DNA in feces, regurgitates, or the gut content of consumers. In providing highly resolved taxonomic information on dietary choice, DNA‐based analysis has become a key approach to unraveling the structure and dynamics of food webs. It is crucial, however, to correctly assign and evaluate trophic linkages among species. Links might be distorted by secondary predation, such as when the DNA of food items that have been consumed by the prey of the predator is detected and incorrectly assigned to the predator's diet. This may become a particular problem when evaluating the diet spectrum of omnivores. We present the first assessment, to our knowledge, of the potential for trophic link errors resulting from secondary consumption of prey in predator–herbivore–plant interactions. Individuals of Drosophila suzukii, fed raspberries (Rubus idaeus) as food items, were freeze‐killed at 0, 6, and 9 hr post‐feeding and then offered to the carabid Pseudoophonus rufipes. Post‐consumption detection intervals (0–128 hr) for DNA of primary prey (D. suzukii) and secondarily consumed raspberry in carabid regurgitates were assessed via PCR assays. Secondary consumption was detected only when D. suzukii flies consumed by the carabid had been feeding on raspberry immediately before they were eaten. The maximum detection time for secondarily consumed food was 32 hr post‐feeding of the carabid, and only in a single regurgitate out of twelve. No secondary food DNA was detected at all when the consumed D. suzukii had digested raspberry for 6 or 9 hr beforehand. These findings would indicate that secondarily consumed plant food is unlikely to contribute to significant error in food web structure. Nevertheless, it is advisable to consider feeding interactions across food webs for estimating the potential of incorrect trophic assignments due to secondary predation events.

Keywords

• feeding experiment
• Harpalus rufipes
• herbivory
• molecular analysis of trophic interactions
• secondary predation