Conclusions
Here, we demonstrate differential expression of specific genes and widespread small, coordinated changes in expression of genes belonging to relevant functional categories in the CNS and eyes following short-term exposure of male I. pygmaeus to OA. We also report genes correlated with both CO2 treatment and OA-affected behaviours, indicating these genes as potentially correlated with CO2-induced behavioural change in I. pygmaeus . The results identify alterations in the transcriptional profile of genes implicated in neurotransmission, neuroplasticity, immune function and oxidative stress. These molecular changes may contribute to OA-induced behavioural change, as suggested by correlations between gene expression profiles, CO2treatment and OA-affected behaviours. Our results build on existing knowledge and provide novel hypotheses for future experiments, including electrophysiological and behavioural tests, to determine the range of processes responsible for behavioural changes in marine animals exposed to projected future OA conditions.