# Past environments modulate response to fluctuating temperatures in a marine fish species, Sebastes fasciatus

## TL;DR

The study shows that past temperature exposure affects how a marine fish species responds to temperature changes, suggesting it may struggle with future ocean warming.

## Contribution

The study reveals how past environments influence thermal plasticity and stress responses in a marine fish species.

## Key findings

- Fish acclimated to higher temperatures showed increased stress-related responses to short-term temperature shifts.
- Transcriptional responses to temperature changes involve dynamic gene functions and sustained gene expression.
- The interaction between long- and short-term temperature exposure significantly affects gene expression.

## Abstract

Predicted ocean warming will impact the survival and structure of various marine organisms, in particular ectotherms. Phenotypic plasticity enables species to cope with environmental changes, providing a vital buffer for evolutionary adaptations. Yet, the dynamics and molecular mechanisms underpinning these plastic responses remain largely unexplored. Here, we assessed the impact of temperature acclimation on the capacity of organisms for thermal plasticity. We conducted a genome-wide transcriptomic analysis on the Acadian redfish, Sebastes fasciatus, exposed to four temperatures (2.5, 5.0, 7.5 and 10.0°C) over a long-term period (up to 10 months) followed on some individuals by a short-term temperature change (+2.5°C or −2.5°C for 24 h), simulating natural temperature variation the species could encounter. Our results showed a dynamic transcriptional response to temperature involving various gene functions. The rapid response to temperature shifts, coupled with the sustained expression of specific genes over an extended period, highlighted the capacity of this species for plasticity in response to temperature changes. We also detected a significant effect of the interaction between the long- and short-term temperature exposures on gene expression, highlighting the influence of the past environment on the response to short-term 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 involvement of stress-related gene functions. This result suggests that temperature conditions predicted for the near future in the Northwest Atlantic will trigger reduced adaptive plasticity to environmental fluctuations, highlighting the vulnerability of this species to ocean warming.

Summary: Thermal plasticity in Acadian redfish is shaped by past temperature exposure, revealing vulnerability to future ocean warming through stress-related transcriptomic responses.