Effects of cadmium in Acartia tonsa : epigenetic and phenotypic responses

Increasing anthropogenic activities are significantly impacting aquatic ecosystems, leading to contamination and potential deleterious effects in organisms. Cadmium, a trace metal with no essential biological role known, is particularly harmful due to its high toxicity, persistence, and bioaccumulation potential. Herein, we assessed the potential link between DNA methylation and different phenotypic endpoints as a response to short-term (48 h) cadmium exposure (238.8 µg/L, corresponding to the pre-estimated immobilization EC20) of the marine copepod Acartia tonsa, a zooplanktonic marine species with important ecological role and established as a model organism in ecotoxicology. Epigenetic changes were assessed through quantification of global 5-mC DNA methylation. Biomarkers of oxidative stress and damage were assessed by measuring glutathione S-transferases (GSTs) activity and the extent of lipid peroxidation, through the TBARS method, while genotoxicity was analyzed by inspecting DNA damage using the comet assay. Additionally, post-exposure swimming behavior of A. tonsa was analyzed by automated video-tracking. Global 5-mC DNA methylation levels slightly decreased among exposed copepods, suggesting a global hypomethylation trend. Phenotypically, this corresponded to a significant increase in genotoxicity, a significant increase in GST activity accompanied by an increase in oxidative damage. Regarding copepods behavior, including swimming distance and swimming speed, an impairment can be noticed, but only at concentrations higher than the EC20, thus higher than those provoking recognizable effects in the other tested biomarkers. This approach supports a better understanding of cadmium s effects on marine copepods, by following adverse outcomes initiated with epigenetic mechanisms at the molecular, biochemical and individual level. As the present work becomes complete with currently ongoing whole epigenome and whole transcriptome analysis, molecular basis for adverse outcome pathways for toxicity caused by stressors such cadmium in copepods will certainly be characterized, which should clarify further the interconnection of the responses found in the present work. Acknowledgements. Project EPIBOOST, funded by the EU through Grant 101078991; CESAM by FCT/MCTES (UIDP/50017/2020 + UIDB/50017/2020 + LA/P/0094/2020); AP by FCT - 2022.10817.BD. JL by national funds (OE), through FCT - framework contract foreseen in Decree- Law 57/2016, changed by Law 57/2017.