Changes in induced-antipredation defense traits and transcriptome regulation of rotifer Brachionus calyciflorus in response to nanoplastics

Nanoplastics (less than 1 µm in size, NPs) have emerged as a significant pollutant in aquatic environment, posing considerable threats to freshwater biota. However, the mechanisms through which NPs modulate the predation responses of these organisms remain poorly elucidated. We investigated the impacts of polystyrene NPs, characterized by a representative particle size (diameter: 50 nm; concentration: 0–8 µg/L), on the anti-predation defense mechanisms of mature rotifer Brachionus calyciflorus against predator of rotifer Asplanchna brightwellii, utilizing transcriptomics to unravel the underlying molecular pathways. Results reveal that the posterolateral spine length and type of B. calyciflorus serve as robust indicators of defensive morphology, even in the presence of NPs exposure. Specifically, increasing concentrations of NPs and predator cues suppressed the defensive responses, which was associated with morphological transformations. This suppression was associated with the down-regulation of the HIF-1α signaling pathway, implicating potentially its role in modulating fight-or-flight responses. Furthermore, we identified functional crosstalk among multiple signaling pathways, including HIF-1α, PI3K-Akt, FoxO, and mTOR, in B. calyciflorus, which may underpin the organism’s responses to polystyrene NP exposure. These findings contribute to the advancement of predictive models to assess the ecological risks posed by polystyrene NPs contamination in aquatic ecosystems.