Thoracic limb activity of Simocephalus vetulus and its descendants is shaped by the combination of delafloxacin and calcium

Abstract Due to its robust antibacterial activity in acidic environments and effectiveness against old fluoroquinolone-resistant bacterial strains, the use of delafloxacin (DFX) is projected to increase in the coming years. Here, we investigated the effect on the thoracic limb rate (TLR) of the water flea Simocephalus vetulus under the combined exposure of DFX (0, 100, 200, and 400 µg L−1) and calcium (Ca) (26 and 78 mg L−1) using Bayesian statistics-based linear models. The findings showed unexpected increases and decreases in the TLR of maternal S. vetulus exposed to DFX in the 26 mg Ca L−1. In the 78 mg Ca L−1 condition, we found a clearer decrease in TLR during DFX treatments. In addition, in the 26 mg Ca L−1, elusive changes in the TLR of neonatal S. vetulus whose mothers were exposed to DFX were observed, whereas the reduced TLR of the neonate, whose mother was exposed to 400 µg DFX L−1, was apparent in the higher Ca condition. While the elevated Ca content did not appear to have a clear effect on organisms’ TLR, it acted as a synergist in conjunction with DFX, leading to a reduction in TLR, the underlying mechanism of which remains poorly understood. The results of our study indicate that DFX may pose an ecological risk as a xenobiotic; therefore, taking into account the abundance of Ca in specific aquatic environments, a comprehensive ecological risk assessment should be conducted. Moreover, the inclusion of Bayesian statistics in ecotoxicological studies is highly recommended to improve data analysis and interpretation.