Adding a marker of gut integrity: an example of experimental augmentation as applied in <i>Eisenia fetida</i>

Gut integrity is critical for organismal health and capacity to host intestinal microbes. Markers of compromised luminal epithelium can serve as quality controls or variables in a wide variety of experiments and species. We combined the Smurf assay with existing bioassays to identify organisms which were moderately affected by experimental treatments, but not so severely as to show physical or behavioral pathology. The Smurf assay is most commonly used to detect impacts of age and disease in model organisms, particularly Drosophila, by feeding water-soluble food dye. Individuals with a compromised luminal epithelium exhibit leakage of gut contents into the body cavity, resulting in discoloration. We added the Smurf assay to standardized ecotoxicological methods for evaluating acute toxicity in the earthworm Eisenia fetida. Adding this marker allowed us to observe variation in our research population quickly and without microscopic examination or dissection.