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.在北美洲，湖白鲑（Coregonus clupeaformis）的种群演化出了同域分布的“侏儒型”与“正常型”两种生态型，二者分别适配湖泊内截然不同的营养生态位。营养特化会对个体产生分化的生理需求，因此与能量代谢相关的基因与表型，是适应性研究的理想候选对象。本研究以加拿大魁北克与美国缅因州的湖白鲑为研究对象，检验其氧气转运相关生理性状的平行分化模式。研究团队观察到两种生态型的红细胞（red blood cell, RBC）形态存在显著分化：在所有被检测的湖泊中，侏儒型个体的红细胞核体积更大，且核面积与细胞总面积的比值显著高于正常型湖白鲑。此外，等电聚焦凝胶电泳结果显示，湖白鲑的血红蛋白蛋白组分存在变异。尽管两种生态型的血红蛋白蛋白组分数量相近，但其组分构成存在差异：相较于正常型个体，侏儒型湖白鲑的阴极组分占比更高。此外，研究团队还在两种生态型的脑组织中观察到血红蛋白基因表达的平行分化：侏儒型湖白鲑的血红蛋白基因呈现显著上调。综合来看，本研究结果表明，氧气转运相关的代谢性状在两种湖白鲑生态型间已发生分化；而跨湖泊观测到的强烈平行分化模式，暗示这一过程由生态驱动的选择压力所介导。本研究还讨论了这些性状在湖白鲑所占据的不同营养生态位中的功能，以及性状可塑性与遗传分化对能量适应性的潜在贡献。