Data from: The temporal window of ecological adaptation in postglacial lakes: a comparison of head morphology, trophic position and habitat use in Norwegian threespine stickleback populations

Background: Studying how trophic traits and niche use are related in natural populations is important in order to understand adaptation and specialization. Here, we describe trophic trait diversity in twenty-five Norwegian freshwater threespine stickleback populations and their putative marine ancestor, and relate trait differences to postglacial lake age. By studying lakes of different ages, depths and distance to the sea we examine key environmental variables that may predict adaptation in trophic position and habitat use. We measured trophic traits including geometric landmarks that integrated variation in head shape as well as gillraker length and number. Trophic position (Tpos) and niche use (α) were estimated from stable isotopes (δ13C, δ15N). A comparison of head shape was also made with two North American benthic-limnetic species pairs. Results: We found that head shape differed between marine and freshwater sticklebacks, with marine sticklebacks having more upturned mouths, smaller eyes, larger opercula and deeper heads. Size-adjusted gillraker lengths were larger in marine than in freshwater stickleback. Norwegian sticklebacks were compared on the same head shape axis as the one differentiating the benthic-limnetic North American threespine stickleback species pairs. Here, Norwegian freshwater sticklebacks with a more "limnetic head shape" had more and longer gillrakers than sticklebacks with "benthic head shape". The "limnetic morph" was positively associated with deeper lakes. Populations differed in α (mean ± sd: 0.76 ± 0.29) and Tpos (3.47 ± 0.27), where α increased with gillraker length. Larger fish had a higher Tpos than smaller fish. Compared to the ecologically divergent stickleback species pairs and solitary lake populations in North America, Norwegian freshwater sticklebacks had similar range in Tpos and α values, but much less trait divergences. Conclusions: Our results showed trait divergences between threespine stickleback in marine and freshwater environments. Freshwater populations diverged in trophic ecology and trophic traits, but trophic ecology was not related to the elapsed time in freshwater. Norwegian sticklebacks used the same niches as the ecologically divergent North American stickleback species pairs. However, as trophic trait divergences were smaller, and not strongly associated with the ecological niche, ecological adaptations along the benthic-limnetic axis were less developed in Norwegian sticklebacks.背景：探究自然种群中营养性状与生态位利用的关联机制，对于理解生物适应性与生态位特化具有重要意义。本研究对25个挪威淡水三脊刺鱼（threespine stickleback）种群及其推测的海洋祖先种群的营养性状多样性进行了描述，并将性状差异与冰后湖泊形成时长相关联。本研究选取不同形成时长、水深及距海距离的湖泊，旨在探究可能影响营养位（trophic position, Tpos）与栖息地利用适应性的关键环境变量。本研究测定了多项营养性状，包括整合头部形态变异的几何形态测量标志点（geometric landmarks），以及鳃耙（gillraker）长度与数量。本研究通过稳定同位素（stable isotope）δ¹³C、δ¹⁵N估算了种群的营养位（Tpos）与生态位利用指数（α）。此外，本研究还将挪威种群的头部形态与北美两个底栖-浮游型物种对（benthic-limnetic species pairs）进行了对比。 结果：研究发现海洋与淡水三脊刺鱼的头部形态存在显著差异：海洋种群拥有更向上倾斜的口裂、更小的眼径、更大的鳃盖以及更深的头部。经体型校正的鳃耙长度在海洋种群中显著长于淡水种群。挪威淡水三脊刺鱼的头部形态所沿的分化轴，与区分北美底栖-浮游型物种对的形态分化轴一致。在此基础上，具有“浮游型头部形态”的挪威淡水三脊刺鱼，其鳃耙数量更多、长度更长，相较于“底栖型头部形态”的种群。“浮游型类群”与更深的湖泊呈正相关关系。种群间的α值（均值±标准差：0.76 ± 0.29）与Tpos值（3.47 ± 0.27）均存在显著差异，且α值随鳃耙长度增加而升高；体型更大的个体营养位也更高。与北美生态分化显著的三脊刺鱼物种对及单一湖泊种群相比，挪威淡水三脊刺鱼的Tpos与α值范围相近，但性状分化程度显著更低。 结论：本研究结果证实了海洋与淡水环境中三脊刺鱼的性状分化：淡水种群在营养生态与营养性状上存在分化，但营养生态与淡水定居时长并无关联。挪威三脊刺鱼所利用的生态位与北美生态分化的物种对一致，但由于其营养性状分化程度更低，且与生态位的关联较弱，因此挪威种群沿底栖-浮游轴的生态适应性发育程度相对更低。