Past environments modulate response to fluctuating temperatures in a marine fish species

The rise in ocean temperatures predicted due to the global warming will impact the survival and structure of various marine organisms, in particular ectothermic organisms. Phenotypic plasticity enables species to cope with environmental changes, providing a vital buffer for evolutionary changes. Yet, the dynamics and the molecular mechanisms underpinning these plastic responses remain largely unexplored. Here, we assessed the impact of acclimation environment on organisms capacity for thermal plasticity. We conducted a genome-wide transcriptomic analysis on the Acadian redfish, S. fasciatus, exposed to four temperatures (2.5, 5.0, 7.5 and 10.0 ) over a long-term period (up to 10 months) followed by an acute temperature change (24 hours), simulating natural fluctuation condition the species could encounter. Our results showed a dynamic transcriptional response to temperature involving various genes functions. The rapid response to temperature shifts, coupled with the sustained expression of specific genes over an extended period highlighted the species capacity for plastic response to temperature changes. We also detected a significant effect of the interaction between the long and short terms temperature exposure on gene expression, highlighting the influence of the past environment on response to acute temperature changes. Specifically, fish acclimated to higher temperatures demonstrated an increased stress-related response to environmental fluctuations, as evidenced by both the shape of their reaction norms and the implication of stress-related gene functions. This result suggests that temperature conditions predicted for the near future in the Northwest Atlantic will trigger less adaptive plasticity to environmental fluctuations, highlighting the species vulnerability to ocean warming.