How does ibuprofen affect the ovaries of the tardigrade Paramacrobiotus experimentalis?

Abstract Paramacrobiotus experimentalis is a gonochoric tardigrade species from Madagascar. The aim of this study was to investigate the effects of ibuprofen on the ovaries, survival, and reproduction of this species. Experimental material was analysed using light, confocal, and transmission electron microscopy. Three ibuprofen concentrations were tested: 0.1 μg/L (a level commonly detected in surface waters worldwide), 16.8 μg/L (typical for rivers in large urban areas), and 1 mg/L (an experimental concentration). The experiment included two exposure periods: short term (7 days) and long term (28 days). Our results showed that none of the tested concentrations affected survival or reproduction at either time point. However, increased oxidative stress was observed after long-term exposure to ibuprofen and after 1 week of incubation at the highest concentration. Ultrastructural analysis revealed endoplasmic reticulum swelling (at the highest concentration during both short- and long-term exposure) and mitochondrial degeneration (at the highest concentration after 28 days). Autophagy and apoptosis were not detected. The cells of the ovary wall were found to be most susceptible to the effects of ibuprofen. The ovary wall plays the role of a barrier protecting germline cells from the effects of stressors.