Data from: Parallelism in the oxygen transport system of the lake whitefish: the role of physiological divergence in ecological speciation

In North America, populations of lake whitefish (Coregonus clupeaformis) have evolved sympatric “dwarf” and “normal” ecotypes that are associated with distinct trophic niches within lakes. Trophic specialization should place diverging physiological demands on individuals; thus, genes and phenotypes associated with energy production represent ideal candidates for studies of adaptation. Here, we test for parallelism in physiological traits involved in oxygen transport in lake whitefish from Québec, Canada, and Maine, USA. We observed significant divergence in red blood cell (RBC) morphology between the ecotypes, with dwarfs exhibiting larger nuclei and a higher nucleus area:total cell area than normal whitefish in all of the lakes examined. In addition, isoelectric focusing gels revealed hemoglobin protein component variation in the whitefish. While dwarf and normal whitefish exhibited a similar number of hemoglobin protein components, the composition of these components differed, with dwarf whitefish bearing a higher proportion of cathodic components compared to the normals. We also observed parallel divergence in hemoglobin gene expression in the brains of dwarf and normal whitefish, with dwarf whitefish exhibiting significant hemoglobin gene upregulation. Together, our results show that metabolic traits involved in oxygen transport have diverged between the whitefish ecotypes and the strong parallelism observed across lakes implicates ecologically driven selection pressures. We discuss the function of these traits in relation to the differing trophic niches occupied by the whitefish and the potential contributions of trait plasticity and genetic divergence to energetic adaptation