Differences in Salinity Tolerance and Gene Expression Between Two Populations of Atlantic Cod (Gadus morhua) in Response to Salinity Stress
Populations of marine fish, even from contrasting habitats, generally show low genetic differentiation at neutral genetic markers. Nevertheless, there is increasing evidence for differences in gene expression among populations that may be ascribed to adaptive divergence. Studying variation in salinity tolerance and gene expression among Atlantic cod (Gadus morhua) from two populations distributed across a steep salinity gradient, we observed high mortality (45% North Sea cod and 80% Baltic Sea cod) in a reciprocal common garden setup. Quantitative RT-PCR assays for expression of hsp70 and Na/K-ATPase α genes demonstrated significant differences in gene regulation within and between populations and treatment groups despite low sample sizes. Most interesting are the significant differences observed in expression of the Na/K-ATPase α gene in gill tissue between North Sea and Baltic cod. The findings strongly suggest that Atlantic cod are adapted to local saline conditions, despite relatively low levels of neutral genetic divergence between populations.
KeywordsGene expression variation Population structure Salinity gradient Salinity tolerance
This study was supported by grants to Peter Foged Larsen from the SLIP Research School under the Danish Network for Fisheries and Aquaculture Research financed by the Danish Ministry for Food, Agriculture and Fisheries and the Danish Agricultural and Veterinary Research Council, the Danish Institute for Fisheries Research, the Elisabeth and Knud Petersens Foundation, and the Idella Foundation. The authors thank Palle Holm Hansen for guidance on fish maintenance, Karen-Lise Dons Mensberg and Dorte Meldrup for assistance in the laboratory, and Henrik Baktoft for graphical assistance.
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