Temperature has profound effects on ectotherm physiology, impacting metabolic and developmental rates, aerobic scope, and inducing cellular stress responses. The resulting phenotypic and fitness consequences ultimately drive population dynamics and species distributions (1). However, the molecular mechanisms underlying physiological responses to temperature are poorly understood (2), as are the spatial scales at which adaptation in thermal responses can occur (3). Yet, this knowledge can help us to understand how populations have adapted to their environments in the past, their contemporary plastic responses, and their potential for future adaptation in the face of anthropogenic climate change. We are interested in how Atlantic cod (Gadus morhua) populations inhabiting different thermal regimes along the Norwegian coast respond differently to changes in temperature. Using gene expression profiles obtained through RNA (transcript) sequencing, we show that rearing at ambient and warmer projected temperatures (+2°C and +4°C) induces changes in gene expression consistent with a severe and accelerated cellular stress response in larval cod while increasing growth and mortality and, thus, likely reducing fitness. We then integrate common-garden experiments across a range of temperatures with transcriptomics to demonstrate the potential for small-scale genetic differences in thermal responses in this highly mobile marine species and provide insight into the molecular basis of thermal adaptation in cod. We aim to inform predictions of the responses of wild cod populations to changing ocean temperatures to enable effective fisheries management in the face of global climate change.
1. Pörtner, H. O. et al. Trade-offs in thermal adaptation: the need for a molecular to ecological integration. Physiol. Biochem. Zool. 79, 295–313 (2006).
2. Logan, C. A. & Buckley, B. A. Transcriptomic responses to environmental temperature in eurythermal and stenothermal fishes. J. Exp. Biol. 218, 1915–1924 (2015).
3. Oomen, R. A. & Hutchings, J. A. Genetic variability in reaction norms in fishes. Environ. Rev. 23, 1–14 (2015).