The effect of the consumption of toxic prey on avian predator physiology
Many insects sequester plant toxic metabolites as a chemical defence against predators. Predators are predicted to include chemically defended prey in their diet if the benefits of gaining nutrients outweigh the costs of ingesting toxins. However, the physiological costs associated with the consumption of prey toxins remain largely unknown, especially when using ecologically relevant predators and naturally occurring levels of toxins. Here, we investigated whether the consumption of chemically-defended wood tiger moths (Arctia plantaginis) influences the physiological state of an avian predator, the great tit (Parus major). We manipulated the moth toxicity by first rearing the larvae in two different diets that varied in pyrrolizidine alkaloid (PA) content, and then manually extracting part of the defensive secretions from half of the moths in both diet groups. This led to four treatments with different moth PA profiles, which were fed to great tits for six consecutive days. After the bird diet manipulation, we collected fecal and blood samples for various physiological analyses of stress and metabolism. We found no significant effects of PA consumption on corticosterone or serotonin concentrations, nor on oxidative stress biomarkers. However, birds exposed to higher PA doses used more of their mitochondrial maximal capacity, which might result from increased metabolic stress. Overall, our results suggest that incorporating some PA-defended insects in the diet does not incur high physiological costs to avian predators, but further studies are needed to explore the costs of consuming a higher number of defended prey and the interactive effects of different prey toxins.