EVALUATING A DNA-BASED APPROACH TO DIET ASSESSMENT
DNA-based approaches have become useful for ecologists to study the diets of wildlife, as molecular tools like qPCR allow researchers to analyze the DNA of prey in a predator’s feces. However, questions about whether these tools can accurately quantify dietary composition through fecal analyses remain largely unanswered. This thesis investigates the ability for qPCR to quantify arthropod prey in feces using a chicken model. Captive chickens (Gallus domesticus) were offered mealworms (MW; Tenebrio molitor) and black soldier fly larvae (BF; Hermetia illucens), and the chickens’ feces were collected for qPCR analyses. A multiplex assay was designed to analyze fecal DNA, which included species-specific assays targeting the cytochrome c oxidase subunit I gene of MWs and BFs. qPCR results were used to meet three objectives. First, I evaluated whether detection and quantification of prey DNA differed between species. Analyzing DNA from hard-bodied arthropods (MWs) may be affected by their more substantial exoskeleton relative to soft-bodied arthropods (BFs). Results showed that in feces, BF DNA was detected more often with a higher but more variable quantity compared to MW DNA. In whole arthropods, a higher and less variable quantity of BF DNA was measured than MW DNA, but the difference between species was smaller in whole arthropods than in feces. Second, I investigated how the time between ingestion of prey and defecation affects detection and quantification of prey DNA. Detection first occurred 30 minutes after feeding and peaked after 4 hours, and trace amounts of DNA were detected on days following consumption. Models showed that time had a negative linear effect on detection and a negative quadratic effect on quantity. Third, I evaluated whether qPCR results could be used to estimate dietary composition. With the results, I was able to accurately characterize the relative composition of mixed diets, and models indicated that estimated and true consumption were significantly related for both species. I have shown that molecular analyses of feces can be used to infer the relative composition of an arthropod-based diet. Results also provide insight on how sampling time may affect conclusions about diet. However, soft-bodied BFs were overrepresented, suggesting a potential bias based on the prey’s body type. To confirm this bias, more research is needed with additional species of each body type, fed to predators with more complex proportions. By addressing questions about the quantitative potential of this molecular technique, my work has contributed to improving inference from DNA-based diet studies.
DNA-based diet assessment, Diet trial, Arthropod prey, Avian predator, Quantitative PCR, Fecal analyses
Master of Science (M.Sc.)